7th International Choanoflagellates & Friends Meeting 24th-27th May 2019 ~ Barcelona
Organizing Committee Omaya Dudin Andrej Ondacka Postdoctoral Researcher Postdoctoral Researcher [email protected] [email protected]
Daniel J. Richter Núria Ros i Rocher Postdoctoral Researcher Postdoctoral Researcher [email protected] [email protected]
Acknowledgements for organizational support Administration & Communication Services - Institute of Evolutionary Biology (CSIC-UPF) The King Lab – UC Berkeley
Sponsors
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7th International Choanoflagellates & Friends Meeting 24th-27th May 2019 ~ Barcelona
Book of Abstracts
Friday, 24th May 2019
The evolutionary origin of animal cell differentiation and synaptic signalling machinery
Pawel Burkhardt Sars International Centre for Marine Molecular Biology, University of Bergen, Norway
Choanoflagellates, the closest unicellular relatives of animals, express many genes previously thought to be animal specific. Strikingly, these tiny protists can alternate between unicellular and multicellular states, making choanoflagellates powerful models to investigate the origin of animal multicellularity, the mechanisms underlying cell differentiation and the ancestry of synaptic protein machinery. We used electron microscopy to reconstruct in three dimensions the total subcellular composition of unicellular and multicellular choanoflagellates as well as the collar cells from a marine sponge. We found differences between single and multicellular choanoflagellates in structures associated with cellular energetics, membrane trafficking and cell morphology and identified a putative novel cell type within rosette colonies. These findings are an important step forward in reconstructing the biology of last common ancestor of the animals and suggests that both, temporal and spatial cell type differentiation was present in the stem lineage leading to animals. In the second part of my talk, I will present our recent discoveries on synaptic protein homologs found in choanoflagellates. We have biochemically and structurally characterized several synaptic protein complexes from choanoflagellates and gained insights into their molecular mechanism. For example, we identified a primordial neurosecretory apparatus and found that the mechanism, by which presynaptic proteins required for secretion of neurotransmitters interact, is conserved in choanoflagellates and animals.
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Saturday, 25th May 2019
Abundance and diversity of loricate choanoflagellates in subtropical oligotrophic South Pacific Ocean
Nina Kamennaya Tel Aviv University
Nutrient-depleted regions dominate the World Ocean because they cover ~40% of the Earth surface. Since nutrient availability generally controls growth of bacterioplankton, concentration of bacteria in surface waters of these oligotrophic regions is particularly low. This makes bacteria a scarcer prey for unicellular eukaryotic predators. To identify the unicellular bacterivores of the oligotrophic regions we flow sorted small, non-pigmented eukaryotes directly from the Atlantic and Pacific Oceans and imaged them using electron microscopy. The sorted eukaryotes routinely comprised loricate Acanthoecida and occasionally non-loricate Craspedida choanoflagellate species. In addition to evident bacterivory, several micrographs suggest that some choanoflagellate species could also feed on armored eukaryotes.
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Choanoflagellate gene expression in the open ocean
Daniel Richter Institute of Evolutionary Biology (CSIC-UPF)
The Tara Oceans expedition sailed the globe over a three-year period, collecting samples from over 150 individual stations. For eukaryotic plankton ranging from 0.8 μm-2 mm, we apply phylogenetic methods to Tara metatranscriptomic data to catalog transcriptional activity in the world’s surface oceans. First, we map Tara Oceans metatranscriptomic sequences to a database of phylogenetic trees for 300 conserved genes to produce a eukaryotic tree of life with each branch weighted by its transcriptional activity. We find that, globally, metatranscriptomes show a similar representation of eukaryotic lineages to Tara metabarcodes (from the V9 region of the 18S locus), indicating that both sources likely reflect the biomass of active cells in the surface ocean. Within the catalog of conserved genes, choanoflagellates represent roughly 1% of global transcript abundance. We next present an analysis of the biogeography of choanoflagellate transcription in the ocean, with the following questions: which species are the most active in different parts of the global ocean? Next, how is the expression of specific functional genes in choanoflagellates (for example, the gene for silicon transport, a requirement for lorica construction) related to local environmental conditions?
2019 International Choanoflagellates & Friends Meeting Page 4 of 38
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Spotlight on Nudiform Choanoflagellates – an Evolutionary Paradox
Sabine Schiwitza, Frank Nitsche University of Cologne
Lorica-bearing choanoflagellates (Acanthoecida) are separated into two families based on their way of lorica production. In the tectiform condition, the mother cell provides a bundle of costal strips prior to cell division to the juvenile cell, whereas nudiform reproducing species have to develop the lorica after division independently. This observation could be confirmed by molecular analysis, but the ecological and evolutionary significance is still under debate. Nudiform choanoflagellates are discussed as an evolutionary paradox as the species are indeed consistent in their way of cell division and lorica production but in terms of morphological characterization they lack coherency. Considering species richness, tectiform choanoflagellates contain a multitude of species compared to nudiforms, where until now only six species were present. With our study we draw attention to the prior neglected and as minor described family of nudiform choanoflagellates. Only recently, we could discover a new sister clade within the nudiforms and described the genus Enibas, comprising until now the species E. tolerabilis and E. thessalia, but with high potential of a greater extent as eDNA data suggest. Interestingly, these species resemble morphologically the tectiform genus Stephanoeca, but show clearly the nudiform cell division and lorica production, supporting the phylogenetic classification within the nudiforms. This particular stephanoecid morphology is now present in both families. It becomes even more obvious that the genus Stephanoeca is in need of revision as we could additionally assign a previous only morphologically described Stephanoeca species to the nudiform family based on molecular data. With our study we could show that the family of nudiform choanoflagellates is broadly underestimated. The combination of molecular and morphological tools together with distinct observations regarding the condition of reproduction will lead to a revision within the Acanthoecida and will help to understand the evolutionary relationship between both conditions.
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Further evidence for phylogenetic and morphological discrepancies within the genus Acanthocorbis
Frank Nitsche, Mona Rosse and Sabine Schiwitza Biological Department, Institute of Zoology, Biocenter Cologne, University of Cologne, Zuelpicher Straße 47b, 50674 Cologne, Germany
The genus Acanthocorbis Hara & Takahashi has one of the most troubled histories within the choanoflagellates. Prior described as Acanthoecopsis Norris it was renamed due to discrepancies based on misleading morphological descriptions. Within the genus Acanthocorbis, nine species are morphologically described but only one, Acanthocorbis unguiculata has been sequenced so far. In 2008, Leadbeater et al. had indication that Acanthocorbis nana might be incorrectly positioned to the tectiform genus as a four-gene analysis placed this species within the nudiforms. A following morphological and molecular analysis gave evidence that this species shows a nudiform lorica reproduction allowing the erection of a new genus, Helgoeca within the nudiform clade. According to latest phylogenetic analyses, Acanthocorbis unguiculata is placed in a clade with Cosmoeca ventricosa, Parvicobicula pedunculata and Stephanoeca apheles with low bootstrap support. In our study we could describe one new Acanthocorbis camarensis-like species with molecular data of the SSU and LSU rDNA which is clustering apart from the other Acanthocorbis species. This polyphyly within loricated choanoflagellates is already known from another genus, the morphological “meltingpot” Stephanoeca. As molecular data of type species are crucial to resolve phylogenetic analyses, our results indicates that only morphological characteristics without observation of “life- cycle”, e.g. reproduction, might be misleading for taxonomic classification. We hypothesize that the morphology of Acanthocorbis as well as of Stephanoeca could be an ancestral state as both are present in the nudiform as well as tectiform condition.
2019 International Choanoflagellates & Friends Meeting Page 6 of 38
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Evolution of metazoan genome regulation, from molecular components to epigenomic landscapes
Arnau Sebé-Pedrós Centre for Genomic Regulation (CRG)
A fundamental question in biology is how the myriad of specialized cell types observed in a multicellular organism is encoded by a single genome sequence. At every generation, diverse regulatory mechanisms orchestrate the spatiotemporal deployment of these diverse cell type programs and starting from a single cell (the zygote). The evolutionary flipside of this developmental process is the emergence of animal multicellularity from single-celled ancestors. Here, we will ask which regulatory genome changes accompanied this unicellular-to-multicellular transition. We will first explore how comparative genomics and proteomics illuminate the evolutionary history of specific chromatin molecular players, including transcription factors, histone modifications and chromatin modifiers. Then, we will examine the configuration of gene regulatory landscapes and genome-wide epigenetic marks in the closest unicellular relatives of animals, using chromatin profiling methods. Finally, we will contrast this unicellular genome regulation with our recent analyses of cell type regulatory programs in early-branching metazoans, using a combination of single-cell transcriptomics and chromatin profiling tools. These results advance in our understanding of the origin and early evolution of animal genome regulation and cell type complexity.
2019 International Choanoflagellates & Friends Meeting Page 7 of 38
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Exploring spatial cell type differentiation in unicellular relatives of animals
Sebastián R. Najle1,2, Thibaut Brunet3, Arnau Sebé-Pedrós4, Linas Mažutis5, Nicole King4, Iñaki Ruiz-Trillo1,6,7 1Institut de Biología Evolutiva (CSIS-Universitat Pompeu Fabra), Barcelona, Spain 2Instituto de Biología Celular y Molecular de Rosario and Facultad de Ciencias Bioquímicas y Farmacéuticas (UNR-CONICET), Rosario, Argentina 3Howard Hughes Medical Institute and the Department of Molecular and Cell Biology, University of California, Berkeley, USA 4Center for Genomic Regulation, Barcelona, Spain 5Institute of Biotechnology, Vilnius University, Vilnius, Lithuania. 6Departament de Genètica, Microbiología i Estadística, Universitat de Barcelona, Spain 7ICREA, Barcelona, Spain.
Cell differentiation is a fundamental attribute of complex multicellular organisms, underpinning the functional specialization of cells and tissues during embryonic development. It has been proposed that animal multicellularity originated by a transition from temporal to spatial cell differentiation. However, it is not clear whether spatial cell-type differentiation is a consequence of multicellularity or if it was already present in the most recent unicellular ancestor of animals. To elucidate this, we aimed at setting up single-cell RNA-Seq methods in the choanoflagellate Salpingoeca rosetta and the filasterean Capsaspora owczarzaki, two of the closest unicellular relatives of animals. These protists display different types of simple multicellularity during their life cycles: clonal colonies in S. rosetta and aggregative colonies in C. owczarzaki. Recent ultrastructural analyses showed the coexistence of morphologically different cell types in S. rosetta colonies, while C. owczarzaki aggregates are assumed to be without spatial cell differentiation. Here, we show our advances in the setup of different single-cell RNA-Seq methods, suitable for each model species. Preliminary analyses of differential gene expression at single-cell resolution of C. owczarzaki aggregates showed an unexpected molecular heterogeneity in the individual cells. The characterization of these putative cell-types, as well as the molecular mechanisms underlying programs of cell differentiation will allow us to better understand the origin of cell-type differentiation during the evolution of animal multicellularity.
2019 International Choanoflagellates & Friends Meeting Page 8 of 38
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Cell organelle composition and chromatin architecture in solitary and colonial choanoflagellates and sponge choanocytes
Benjamin Naumann Institute of Zoology and Evolutionary Research
Choanoflagellates are the closest relatives to the multicellular animals, the Metazoa. Despite first described as single-celled organisms, some choanoflagellates have the ability to form colonies consisting of more than 100 cells. In contrast to metazoans, these choanoflagellate colonies have been described to consist of similar cells that show no sign of differentiation into different cell types. Therefore, cell differentiation and the presence of different cell types is used as one of the basic features to define the Metazoa. Recently, the discovery of single cells in colonies of the choanoflagellate Salpingoeca rosetta that exhibit a unique cell form challenges this view. We therefore asked: How similar are the cells within a colony really compared to solitary S. rosetta and sponge choanocytes? To answer this question, we used high-resolution TEM serial sections through three S. rosetta colonies (7, 10 and 12 cells), three solitary cells and five choanocytes of the sponge Oscarella carmela to reconstruct the organelle composition (food vacuoles, mitochondria, nuclei, etc) of each cell. Additionally, we reconstructed the microscopic euchromatin/heterochromatin composition in each nucleus to compare the diversity of chromatin ratios and architecture of differentiated sponge choanocytes to “undifferentiated” S. rosetta cells.
2019 International Choanoflagellates & Friends Meeting Page 9 of 38
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Evolution of Runx and NF-kB developmental Transcription Factors and their role in Capsaspora owczarzaki
Núria Ros i Rocher Institute of Evolutionary Biology (CSIC-UPF)
The origin of animal multicellularity is a major question in biology. Recently, new genome data from extant unicellular relatives of animals revealed that the single-celled animal ancestor possessed a complex repertoire of developmental transcription factors (TFs), key for animal multicellularity. For example, the Runx and the NF-kB developmental TF families, which have myriad roles in cell fate determination, cell differentiation and stress responses in animals, are some representatives of the pre-metazoan developmental toolkit. Both TFs were identified in the filasterean amoeba Capsaspora owczarzaki, one of the closest unicellular relatives of animals. Interestingly, Capsaspora’s Runx and NF-kB homologs present different transcriptional levels and protein abundance across its different life stages. Here, to gather additional evidence of their putative function as transcriptional regulators in a unicellular context, we assessed their binding preferences and downstream regulatory networks in Capsaspora through localisation and Chromatin Immunoprecipitation coupled with high-throughput sequencing (ChIP-seq) experiments across Capsaspora life stages. Preliminary results and implications will be presented and discussed.
2019 International Choanoflagellates & Friends Meeting Page 10 of 38
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Functional studies of the Hippo pathway in Capsaspora and Choanoflagellates
Jonathan Phillips UT Southwestern Medical Center
Little is known about the evolutionary origins of signaling pathways that regulate tissue size by inhibiting proliferation. The Hippo pathway plays a key role in regulating tissue size and tumorigenesis in animals by inactivating the proliferation-promoting transcriptional coactivator Yorkie by phosphorylation-mediated cytoplasmic sequestration and degradation. Interestingly, the core Hippo pathway is conserved in the closest unicellular relatives of animals but not in more basal organisms such as yeast. We have been investigating the Hippo pathway in the filasterean Capsaspora owczarzaki and in choanoflagellates to understand the ancestral functions and evolutionary origins of the Hippo pathway and to identify potentially conserved physiological signals that might regulate this pathway. An antibody against Capsaspora Yorkie (coYki) shows nucleoplasmic staining in cells at low density, suggesting that coYki is transcriptionally active in these cells. Interestingly, in high density regions of cell colonies coYki shows a nucleolar localization, indicating that coYki localization is regulated by cell density and suggesting that localization in the nucleolus may be a mechanism of inactivating Yorkie. Capsaspora forms multicellular aggregate structures, and coYki shows a nucleolar localization in these structures as well. We have developed stable transgenic cell lines and gene targeting techniques in Capsaspora that will allow us to better characterize the regulation and function of the Hippo pathway in the future. In the choanoflagellate Salpingoeca rosetta, a Yorkie ortholog (srYki) localizes to the nucleus, and Chip-seq experiments using an antibody against srYki reveal a set of putative srYki targets that show enrichment for genes encoding glycosidases and transcription factors. Our results indicate an ancient origin of the regulation of Hippo signaling by cell density and suggest that, analogous to Hippo pathway function in animals, the Hippo pathway in unicellular organisms may function in the regulation of proliferation in multicellular structures.
2019 International Choanoflagellates & Friends Meeting Page 11 of 38
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Insights into the origin of postsynaptic signalling machineries from choanoflagellates
Tarja Hoffmeyer1,2,3, Fiona Savory2, Mads Grønborg4, Thomas Richards2 and Pawel Burkhardt1 1 Sars International Centre for Marine Molecular Biology, University of Bergen, Thormøhlensgt. 55, N- 5006, Bergen, Norway 2 Living Systems Institute, University of Exeter, Stocker Road, Exeter EX4 4QD, United Kingdom 3 Marine Biological Association of the United Kingdom, The Laboratory, Citadel Hill, Plymouth PL1 2PB, United Kingdom 4 Novo Nordisk A/S, Discovery Biology & Technology, Discovery ADME, Novo Nordisk Park, 2760, Måløv, Denmark
Scaffolding proteins at the postsynapse organise signalling complexes that enable synaptic transmission and synapse maturation. Choanoflagellates – the closest single celled relatives of animals – encode many homologs of these postsynaptic scaffolding proteins in their genomes. We hypothesise that some of the protein interactions required for synaptic functioning existed prior to the evolution of neurons in the last common ancestor of animals and choanoflagellates. At the postsynapse, the interaction of the scaffolding proteins Homer and Shank is crucial, because they interconnect core postsynaptic density complexes to downstream signalling, i. a. controlling cytoskeleton remodelling and calcium signallinga,b. Using isothermal titration calorimetry, we now show that Homer from the choanoflagellate Salpingoeca rosetta is capable to bind rat Shank1. Combining this technique with ancestral protein reconstruction, we are currently investigating the evolutionary history of this interaction. Another postsynaptic scaffolding protein, PSD-95 is important for recruiting and anchoring ionotropic glutamate receptors in postsynaptic membranes and organising several postsynaptic complexesc. We used co-immunoprecipitation in combination with LC-MS/MS mass spectrometry to investigate in vivo interaction partners of the Dlg/PSD-95 homolog of S. rosetta. Our analysis revealed around forty interaction partners, one of which was identified as member of the p55 family of scaffolding proteins. In animals, proteins of this family were found in connection with Dlg homologs in animal epithelia supporting tight junction formationd and in postsynapses supporting adhesion of pre- and postsynaptic terminalse. Our work will help to resolve which protein interactions were present in the last common ancestor of animals and choanoflagellates and served as a foundation for the establishment of postsynaptic signalling machineries in the animal lineage.
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a Naisbitt, S., Eunjoon, K., Tu, J.C., Xiao, B., Sala, C., Valtschanoff, J., Weinberg, R.J., Worley, P.F., and Sheng, M., 1999. Shank, a novel family of postsynaptic density proteins that binds to the NMDA receptor/PSD-95/GKAP complex and cortactin. Neuron, 23(3), pp.569–582. b Sala, C., Piëch, V., Wilson, N.R., Passafaro, M., Liu, G., and Sheng, M., 2001. Regulation of dendritic spine morphology and synaptic function by Shank and Homer. Neuron, 31, pp.115–130. c Chen, X., Levy, J.M., Hou, A., Winters, C., Azzam, R., Sousa, A.A., Leapman, R.D., Nicoll, R.A., and Reese, T.S., 2015. PSD-95 family MAGUKs are essential for anchoring AMPA and NMDA receptor complexes at the postsynaptic density. Proceedings of the National Academy of Sciences of the United States of America, 112(50), pp.E6983–E6992. d Stucke, V. M., Timmermann, E., Vandekerckhove, J., Gevaert, K, and Hall, A., 2007. The MAGUK protein MPP7 binds to the polarity protein hDlg1 and facilitates epithelial tight junction formation. Molecular Biology of the Cell, 18, pp. 1744-1755. e Rademacher, N., Schmerl, B., Lardong, J.A., Wahl, M.C., and Shoichet, S.A., 2016. MPP2 is a postsynaptic MAGUK scaffold protein that links SynCAM1 cell adhesion molecules to core components of the postsynaptic density. Scientific Reports, 6(1), p.35283.
2019 International Choanoflagellates & Friends Meeting Page 13 of 38
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Gradual evolution of the cell cycle regulation during the transition to animal multicellularity
Alberto Perez Posada Institute of Evolutionary Biology (CSIC-UPF)
In animal cells, the progression through the cell cycle is coordinated by activity of cyclins and cyclin-dependent kinases (CDKs). Temporal waves of cyclin-CDK activity orchestrate other cell cycle events, such as temporal gene expression program. In contrast to animals, which possess multiple members of cyclin and CDK families, active at distinct stages of the cell stage, unicellular yeasts contain a smaller cyclin-CDK repertoire. To characterize the evolution of the cell cycle machinery, we characterized the cell cycle-periodic gene expression in a close unicellular relative of animals, the filopodiated amoeba Capsaspora owczarzaki. We performed time-series RNA-seq in synchronized cell cultures, identifying a set of 801 periodic genes that grouped into five clusters of expression over time. Comparison to datasets from human cells and yeasts revealed that globally, the periodic transcriptional program of Capsaspora is more similar to that of animal cells. Furthermore, we found that orthologues of cyclin A, B and E show the same temporal expression order as in animals. The presence of one single ancestral CDK1-CDK3 ortholog in Capsaspora suggests that this CDK is able to interact with cyclins A, B and E in the same temporal order as in animals, leading to a gradual evolutionary scenario where CDKs expanded and specified in function after the last unicellular ancestor of animals.
2019 International Choanoflagellates & Friends Meeting Page 14 of 38
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Corallochytrium limacisporum, a newly emerging model system to address questions of animal origin
Aleksandra Kożyczkowska, Sebastian R. Najle, Eduard Ocaña-Pallarés, Elena Casacuberta, Iñaki Ruiz-Trillo Institute of Evolutionary Biology (CSIC-UPF)
How animals emerged from a single-celled ancestor is one of the most pivotal events in the history of life. Recent genome data from the unicellular relatives of animals have revealed the presence of some genes involved in multicellularity and animal development previously thought to be animal- specific. What remains unclear is the role of those genes in the unicellular relatives of animals, and how they were co-opted at the onset of Metazoa. To address those questions, we need to perform functional studies on those taxa. One of the earliest branching lineages among unicellular relatives of animals is the Corallochytrea, with only two taxa described so far, Corallochytrium limacisporum and Syssomonas multiformis. Corallochytrium is a understudied marine free-living walled saprotroph, that in addition to its key phylogenetic position, has other features that make it relevant to be developed as a model organism: a peculiar and still uncharacterized life cycle that goes through rounds of binary divisions forming duets or tetrads, a well annotated genome which contains both, syntenic regions with other unicellular eukaryotes and several conserved homolog genes with animals. C. limacisporum can be cultured in axenic conditions, in both, liquid and solid medium facilitating the isolation of clonal lines. In order to perform functional studies on these taxa we need to develop genetic tools. We here present a reliable transfection protocol for Corallochytrium for both transient and stable transfection. We have also characterized four independent transformed lines. Our data shows that stable transfection occurs by integration into the genome in multiple copies and presumably episomes can be inherited in a stable manner. We have also developed vectors with different endogenous promoters in order to regulate the expression of desired genes, as well as a battery of cassettes tagging different cellular proteins, that will serve for a better understanding of its life cycle. Progress and the potential implications of our research will be presented and further discussed.
2019 International Choanoflagellates & Friends Meeting Page 15 of 38
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Methodological approach for the obtention of genomic data from polyxenic cultures of unicellular Opisthokonta
Eduard Ocaña-Pallarès Institute of Evolutionary Biology (CSIC-UPF)
Multicellularity is a major evolutionary transition, responsible of the emergence of complex living forms such as animals. Despite it occurred roughly 20 times in life history, it is in eukaryotes where multicellularity achieved highest levels of complexity. Opisthokonta represents a great phylogenetic framework to study the genomic footprints behind this transition, as it includes two distinct multicellular lineages, animals and fungi, both surrounded by early-branching unicellular relatives. In theory, the comparison between the genomes of the last unicellular and the first multicellular ancestors would reveal which innovations were crucial for the appearance of multicellularity. As these genomes are not accessible, we need to reconstruct them from a well- sampled representation of their descendants. This implies that not only genomic data from animals and multicellular fungi is needed, but also from their immediate unicellular relatives. Unfortunately, the acquisition of genomic data from unicellular Opisthokonta is problematic as they are usually maintained in cultures with a large and heterogeneous population of contaminant species. A methodological protocol and bioinformatics pipeline used to generate good quality genomes from polyxenic cultures of three filasterean and one nucleariid species will be presented. Preliminar results from comparative genomics analyses including these four genomes will also be shown.
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TBD
Nicole King Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA
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Sunday, 26th May 2019
Evolution of programmed cell death machinery around the emergence of animal multicellularity
Michelle M. Leger1, Iñaki Ruiz-Trillo1,2,3 1 Institute of Evolutionary Biology (CSIC-UPF), Barcelona, Spain 2 Department of Genetics, University of Barcelona, Barcelona, Spain 3 Catalan Institution for Research and Advanced Studies (ICREA), Barcelona, Spain
Programmed cell death (PCD) involves the death of specific cells in a controlled manner, in response to extrinsic or intrinsic triggers. It is an essential function in animals, where it regulates normal development, responses to cell damage, and cell turnover. Accordingly, the PCD machinery present in the unicellular ancestors of animals was likely critical to the appearance of complex multicellularity in animals. Choanoflagellates, filastereans, ichthyosporeans, and pluriformeans are the closest unicellular relatives of animals; at least some members of each group exhibit simple multicellularity during some stages of their life cycle. As a result, they present an excellent opportunity to understand the elements of the PCD repertoire that were present in the unicellular ancestors of Metazoa, and the functional and regulatory changes that they might have undergone during the emergence of animal multicellularity. Using a comparative genomics approach, we have surveyed known PCD-related proteins and protein domains across Opisthokonta. We show that the best-known animal PCD pathway, apoptosis, is a true animal innovation, but that both animal-specific and more widely conserved elements of PCD machinery were already present prior to the emergence of animals.
2019 International Choanoflagellates & Friends Meeting Page 18 of 38
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Phylogenomic reconstruction of Holozoa through the lens of metagenomics: The genome of the first filasterean parasite provides insights into the unicellular ancestry of animals
Konstantina Mitsi1, Ander Urrutia2, Michelle Leger1, David Bass2,3 and Iñaki Ruiz- Trillo1,4,5 1Institut de Biologia Evolutiva (CSIC-Universitat Pompeu Fabra), Passeig Marítim de la Barceloneta, 37- 49, 08033 Barcelona, Spain. 2Centre for Environment, Fisheries and Aquaculture Science, Weymouth, Dorset, UK 3Department of Life Sciences, Natural History Museum London, London, UK 4Departament de Genètica, Universitat de Barcelona, Avinguda Diagonal 643, 08028, Barcelona, Spain. 5Institució Catalana de recerca I Estudis Avançats (ICREA), Passeig Lluís Companys, 23, 08010 Barcelona, Spain.
The eukaryotic group Holozoa comprises animals and their unicellular relatives, namely Choanoflagellates, Filasterea and Teretosporea (Ichthyosporea+Pluriformea). Unicellular holozoans hold a phylogenetic position that is key to addressing a long-standing open evolutionary question: the transition to animal multicellularity. To expand the extant holozoan genomic dataset, here we report the morphology, nuclear and mitochondrial genomes of Txikispora sp.. Txikispora sp. is known to infect at least two amphipod genera, Echinogammarus sp. and Orchestia sp. collected from the southwest coast of United Kingdom. It is the first confirmed filasterean parasite as it triggers host response in the form of granuloma formation and melanization, reducing host motility and general fitness. Phylogenomic reconstruction based on 85 single-copy protein domains and 23,526 aa positioned this novel unicellular holozoan species as an early-branching filasterean. The genome was acquired following a metagenomic pipeline, an approach that is commonly used to describe complex prokaryotic communities but is still in limited use for studies of eukaryotes. Comparative analysis revealed that the Txikispora sp. genome encodes most genes involved in the flagellar toolkit as well as with the majority of genes previously identified as the multicellular toolkit. The latter include the integrin adhesome and many developmental transcription factors. In addition, genes involved in meiotic recombination were identified. Overall, our results add to our understanding of the genomic repertoire of the last unicellular common ancestor of animals, reinforce the current holozoan phylogeny by expanding the available dataset and provide insights into the mechanisms that facilitate a parasitic lifestyle in a filasterean.
2019 International Choanoflagellates & Friends Meeting Page 19 of 38
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Phylogenomics challenges choanoflagellate evolution and reveals new insights into the pre-metazoan genetic tool-kit.
David López-Escardó Department of Marine Biology and Oceanography, Institute of Marine Sciences (ICM)–CSIC
Choanoflagellates are the closest unicellular relatives of animals. Therefore, the internal phylogeny of choanoflagellates, as well as their genomic content are crucial to better understand the early origins of animal multicellularity. So far, there are only two choanoflagellate taxa with whole genome sequences (Monosiga brevicollis and Salpingoeca rosetta), representing a narrow fraction of choanoflagellates diversity. In this work, we have expanded the available genomic information of choanoflagellates by sequencing four single-cell amplified genomes (SAGs) collected during the TARA Oceans expedition. The SAGs were chosen to expand phylogenetically our previous knowledge, with one of them being and early-branching acanthoecid and the third most abundant choanoflagellate in TARA Oceans. This SAG and an early-branching clade 1 craspedidan were complete enough to be used in our phylogenomics analysis. Our newly updated choanoflagellate tree, that includes these new SAGs and all the available transcriptomic data of choanoflagellates, breaks the monophyly of Craspedida and establishes Codosiga hollandica as the earliest-branching choanoflagellate. This suggests a non-thecated colonial and freshwater ancestor of choanoflagellates, opening new hypotheses regarding the ecological context in which the ancestors of choanoflagellates and animals could have emerged. Finally, a comparative genomic analysis revealed a pre-metazoan origin of protein domains that are involved in the organization of animal multicellularity, such as transcription factors related to development (Nucleophosmin and Smad), protein domains related to immunological and sperm functions (IRF and TILa respectively), and genes that expand the neural pre-metazoan toolkit (NKAIN and Praxilin). Overall, our new choanoflagellate genomes have provided a new phylogenetic tree of this group, as well as expanded the list of genes and protein domains with a pre-metazoan origin.
2019 International Choanoflagellates & Friends Meeting Page 20 of 38
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Evolution and Function of the ichthyosporean microRNA system
Jon Bråte University of Oslo
We have recently discovered that ichthyosporeans express microRNAs (miRNAs) and that they also contain homologs of the protein machinery which generates miRNAs in animals, the Microprocessor. This showed that the animal miRNA system actually evolved at least as early as at the emergence of Holozoa, but exactly how early is still not known. We also do not know anything about the function of the ichthyosporean miRNAs. Here we have searched for the Microprocessor components in all available eukaryote proteomes. We find the entire Microprocessor, in addition to expressed miRNAs, among amoebozoans, haptophytes and stramenopiles, i.e. in different eukaryote supergroups and on both sides of the presumed eukaryote root. Hence, the ancestor of the eukaryote supergroups likely possessed both miRNAs and the entire Microprocessor. Furthermore, we have found evidence that ichthyosporean miRNAs induces cleavage of mRNAs targets. A mechanism which is similar to that found in cnidarians and in plants. Altogether, this suggests an ancient functional link between the Microprocessor and miRNAs in eukaryotes, which strengthens the hypothesis that a miRNA-based gene regulatory system evolved before the divergence of animals and plants. And that the ancestral function of miRNAs in both these lineages was likely cleavage of target mRNAs.
2019 International Choanoflagellates & Friends Meeting Page 21 of 38
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Light-regulated collective contractility in a multicellular choanoflagellate
Tess Linden & Thibaut Brunet Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA
Collective cell contractions that generate global tissue deformations are a signature feature of animal movement and morphogenesis. Nonetheless, the ancestry of collective contractility in animals remains mysterious. While surveying the Caribbean island of Curaçao for choanoflagellates, the closest living relatives of animals, we isolated a previously undescribed species (Choanoeca flexa sp. nov.), that forms multicellular cup-shaped colonies. The colonies rapidly invert their curvature in response to changing light levels, which they detect through a rhodopsin-cGMP pathway. Inversion requires actomyosin-mediated apical contractility and allows alternation between feeding and swimming behavior. C. flexa thus rapidly converts sensory inputs directly into multicellular contractions. In this respect, it may inform reconstructions of hypothesized animal ancestors that existed before the evolution of specialized contractile cells.
2019 International Choanoflagellates & Friends Meeting Page 22 of 38
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The coenocytic cycle of the ichthyosporean Sphaeroforma arctica
Andrej Ondracka Institute of Evolutionary Biology (CSIC-UPF)
Among unicellular relatives of animals, the clade ichthyosporeans contain mostly parasitic microorganisms that share a life cycle which contains a multinucleate stage, generated by rounds of nuclear divisions without accompanying cytokinesis (coenocytic). Among ichthyosporeans, Sphaeroforma arctica represents a uniquely tractable coenocytic life cycle which can be easily synchronized in cultures and exhibits highly regular morphology and timing. First, I will present our work on quantitative characterization of the coenocyte growth and nuclear division cycles, which revealed that the nuclear division cycles in Sphaeroforma arctica are driven by a clock mechanism. In the second part, I will present the transcriptomic characterization of the coenocytic cycle and cellularization of the coenocyte, which revealed that the mechanisms of cellularization are likely conserved between animal coenocytes in early embryonic development and ichthyosporeans.
2019 International Choanoflagellates & Friends Meeting Page 23 of 38
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How one becomes many: cellularization in the ichthyosporean Sphaeroforma arctica
Omaya Dudin Institute of Evolutionary Biology (CSIC-UPF)
In animals, cellularization of a coenocyte is a specialized form of cytokinesis that results in the formation of a polarized epithelium during early embryonic development. It is characterized by the coordinated assembly of an actomyosin network, which drives inward membrane invaginations. Here, we wondered if the ichthyosporean coenocyte undergoes a similar process. Using Sphaeroforma arctica, we show that cellularization involves coordinated inward plasma membrane invaginations dependent on an actomyosin network. This leads to the formation of a polarized layer of cells resembling an epithelium. By using inhibitory molecules, we demonstrate that cellularization depends on the sequential role of Arp2/3 complex, Formins and Myosin II in organizing the actomyosin network. Finally, using experimental evolution, we successfully generated several mutants with cell release defects leading to the formation of clonal multicellular clumps. Such mutants will allow further investigation of the cellularization process and generate a strong hypothesis on the steps required for the emergence of animal multicellularity.
2019 International Choanoflagellates & Friends Meeting Page 24 of 38
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Monday, 27th May 2019
Sphingolipids and sphingosine-type signaling molecules of microbial origin modulate the morphogenesis of choanoflagellates
L. Raguz,̌ 1 D. Leichnitz,1 E. Ireland,2 Chia-Chi Peng,1 N. King,2 C. Beemelmanns1 1Chemical Biology of Microbe-Host Interactions, Hans-Knoll̈ -Institute (HKI), Beutenbergstrasse 11a, 07745 Jena, Germany. 2Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA.
Sphingolipids and sphingosine-type compounds are widely distributed in nature. They have been isolated from mammals, marine organisms, plants, fungi and recently from bacteria, where they convey a diverse set of signal transduction and stress response pathways and have profound physiological impacts.1 Despite their recognized importance fully characterized examples of structure-activity relations are still rare. Recently, novel sphingolipid derivatives were isolated from Algoriphagus machipongonensis a Gram-negative bacterium of the Bacteroides genus, whose members often comprise 50% of the gut community in vertebrates and invertebrates.2a First bioactivity studies demonstrated that two specific sulfonolipids induce cell differentiation in the predatory eukaryote choanoflagellate Salpingoeca rosetta. 2b The same studies also showed that a related molecule, named IOR-1, inhibited the cell differentiation to the colonial stage.2c We have now established a synthetic route towards bacterial sphingolipids as well as derivatives to determine the absolute configuration of the signaling molecules, to analyze the structure-activity relationship (SAR) of these highly potent inducers and to identify the targets of the molecules within S. rosetta. The synthetic compounds also allow us now to determine the abundance within the different microbial producers, which will give us in depth insight in the morphogenesis process and predatory behavior of S. rosetta.
2019 International Choanoflagellates & Friends Meeting Page 25 of 38
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Reconstructing the evolutionary origin of synaptic protein complexes
Ronja Göhde and Pawel Burkhardt Sars International Centre for Marine Molecular Biology, University of Bergen, Bergen 5006, Norway
The critical step in synaptic transmission is the fusion of synaptic vesicles with the presynaptic membrane in order to release their content into the synaptic cleft. This event incorporates several critical proteins which have been shown to be conserved from animals to choanoflagellates, the closest unicellular relatives of animals. These findings suggest that most of the proteins responsible for synaptic transmission evolved prior to the origin of the first animals. We aim to test this hypothesis by investigating synaptic protein homologs in the choanoflagellate Salpingoeca rosetta, which can form free swimming colonies by cell division. Studying synaptic protein homologs of S. rosetta offers the great advantage of investigating the origin of the synaptic machinery in direct association with cell adhesion and simple multicellularity. Within the scope of this study high-throughput proteomics combined with co-immunoprecipitation will be used to analyse the proteome of single and colonial cells of S. rosetta with special focus on synaptic protein homologs as well as their interactions. Using these techniques enabled the identification of conserved and previously unknown interaction partners of synaptobrevin, the key protein in synaptic vesicle fusion. In order to enable a comparison with synaptic vesicles, protein compositions and quantities of putative secretory vesicles of S. rosetta will be analysed. Overall, this study intends to elucidate the biology and functional evolution of ancestral synaptic proteins, which promises to reveal core functions of mammalian synapses at the molecular level.
2019 International Choanoflagellates & Friends Meeting Page 26 of 38
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Identification and biosynthesis of morphogenic natural products of bacterial origin
Christine Beemelmanns Hans-Knöll Institute
We have chosen the marine polyp Hydractinia echinata as a model system to study the chemical communication between the eukaryotic host and its associated microbiome. The life cycle of the hydroid polyp includes the bacterially induced transition of the motile larvae to the sessile reproductive phase (polyp). The larva develops into a primary polyp only in response to a chemical cue/specific molecule provided by associated environmental bacteria. We used a culture- dependent and independent approach to identify associated microbes. Subsequent bioassay- guided analysis revealed a new set of morphogenic compounds inducing the morphogenesis to the adult stage.
2019 International Choanoflagellates & Friends Meeting Page 27 of 38
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Investigation of molecular cues that drive aggregation in Capsaspora owczarzaki aggregation
Joseph P. Gerdt, Núria Ros-Rocher, Iñaki Ruiz-Trillo, Jon Clardy Harvard / Indiana University
Regulated cellular aggregation and disaggregation are essential processes in animal development. However, animals are not the only organisms to employ cellular aggregation. This phenomenon is exhibited by a wide range of organisms, including the filasterean Capsaspora owczarzaki. Capsaspora is a predatory protozoan and one of the closest living unicellular relatives of animals. It presents a complex genetic repertoire of genes previously thought to be animal-specific, and a differentially regulated life cycle, including a dramatic aggregative phenotype. Capsaspora aggregates exhibit increased expression of genes related to cell-cell adhesion in animals. Therefore, the study of Capsaspora aggregation will yield insight to the evolution of cellular aggregation phenotypes. However, little is known about the molecular cues and/or signaling agents that trigger aggregate formation and disassociation in Capsaspora. In this work, we sought to characterize the molecules involved in Capsaspora aggregation and uncover means by which the aggregation phenotype is regulated. We have found that Capsaspora aggregation requires at least two environmental cues. Progress toward identification of these cues and their implications will be discussed.
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Poster Abstracts
Is gene transfer a source of ecological adaptation in eukaryotes? The case of nitrate metabolism Eduard Ocaña-Pallarès Institute of Evolutionary Biology (CSIC-UPF)
Nitrogen is an essential element for life. However, while it constitutes about 80% of the atmosphere, only a handful of organisms can fix it directly. Therefore, most taxa require alternative nitrogen sources that are mostly produced through biological reactions. Because nitrate is the most abundant source in the oceans and in many terrestrial environments, characterizing its metabolism is important to address the role of a given organism in an ecosystem. We here assessed the distribution of the genes involved in nitrate assimilation (NAPs) in eukaryotes. We found that this metabolic pathway is completely absent in phagotrophic lineages while is strongly associated with autotrophy and osmotrophy. The phylogenetic signal indicate multiple transfers of NAPs between osmotrophic and autotrophic lineages, the last possibly related with the endosymbiotic events that led to the origin of complex plastids. These results suggest that gene transfer could be an important source of adaptive ecological traits also for eukaryotes. It is also relevant the finding of NAPs in two recently sequenced ichthyosporean species which are able to grow in a nitrate minimal medium. Interestingly, they present a novel nitrate reductase that replaced the canonical C-ter region for the N-ter region of the nitrite reductase. While most of ichthyosporeans are described as parasites, the metabolic complexity of these two species agrees with environmental data suggesting that non-parasitic members may exist. As ichthyosporeans and animals are closely related in the eukaryotic tree, these findings have implications for the potential living styles of the animal ancestors.
2019 International Choanoflagellates & Friends Meeting Page 29 of 38
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Warm water loricate choanoflagellate biodiversity
Helge Abildhauge Thomsen1 and Jette B. Østergaard2 1Technical University of Denmark, National Institute of Aquatic Resources (DTU Aqua), Kemitorvet, Bygning 201, DK 2800 Kgs. Lyngby, Denmark 2Nørrebrogade 52a 5th, 2200 Copenhagen N, Denmark
In an effort to make the best use of extensive nanoflagellate sampling carried out during the last four decades, we are currently in the process of compiling loricate choanoflagellate biodiversity data from warm water realms. The material originates from the Indian Ocean (the Andaman Sea and West Australia), the Atlantic Ocean (Sargasso Sea), the Mediterranean Sea (Alexandria), the Caribbean Sea, and the equatorial Pacific Ocean. Our analyses are purely qualitative and based on shadow cast TEM whole mounts and LM inspection of material ’mounted in air’ on coverslips. Our aim is a ‘monographic’ treatment of the loricate choanoflagellate warm water communities, that can become a morphospecies frame of reference for future research based on both traditional microscopical descriptive techniques and molecular tools. The total number of ‘warm water’ species encountered is close to 80. Approximately 20 of these are new to science and will be formally described as work progresses. This will bring the total number of described loricate choanoflagellate species close to 150. We are convinced that it is preferable to the science community that the morphospecies diversity is accounted for as best as possible, even when there is (regrettably) no molecular data to be presented in parallel. For obvious reasons (less than 15% of the species described have so far associated sequence data) we have taken a conservative approach when describing new species and allocating these to genera, realizing that once molecular data becomes much more comprehensive, phylogenetic patterns will emerge that will necessitate a thorough redeployment of species and genera. Here we present the current status with regard to our challenging endeavour.
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Detection of Horizontal Gene Transfer in the choanoflagellate Salpingoeca rosetta
Danielle Mateo Matriano Marine Science Institute
Horizontal gene transfer (HGT) is common in prokaryotes but its scale and role in the evolution of most eukaryotes remain obscure. Just like other phagotrophic choanoflagellates, the genome of Salpingoeca rosetta may contain a rich repertoire of transferred bacterial genes. In this study, we will identify candidate HGTs in the genome of S. rosetta using sequenced-based (“parametric”) and phylogenetic methods. We will be analysing homologs of these putative HGTs in other choanoflagellate species and identifying its potential functions to the host. We hypothesize that horizontally transferred genes may have contributed to the ability of S. rosetta to adapt to diverse ecological niches through the development of modified metabolic and morphological features.
2019 International Choanoflagellates & Friends Meeting Page 31 of 38
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Loricate choanoflagellates of the Atlantic open ocean
Nina Kamennaya Tel Aviv University
Oceanic motile loricated (Acanthoecida) choanoflagellates are generally considered to be bacterivores. Only occasionally have they been shown to consume eukaryotic picoplanktonic algae, e.g. Micromonas. Electronic micrographs of oceanic choanoflagellates, flow sorted from the temperate South Atlantic Ocean, suggest that Acanthoecida choanoflagellate could also feed on larger armoured phytoplankton. Hence prey spectrum of choanoflagellates could be considerably broader than we thought.
2019 International Choanoflagellates & Friends Meeting Page 32 of 38
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The origin of retrotransposons in choanoflagellates
Juan José Ginés Rivas University of Huddersfield
Choanoflagellatea is the taxonomic order of protist closer to Metazoa. They are unicellular organisms, able to live in fresh and marine water, either as free-living organisms or forming colonies. Retrotransposons are repetitive sequences of DNA, with transposition carried out with the help of the Reverse Transcriptase enzyme. The copy-paste mechanism spreads new copies through the genome. In particular, the LTR retrotransposons resemble the vertebrate retroviruses but without an envelope-like gene. The evolutionary importance of retrotransposons arises from their ability to produce deleterious and adaptive mutations. Retrotransposons, as host genes, could have codon usage bias, or the use of certain codons over others in the degenerated genetic code, that are usually different of each other in species due to selection or mutation pressure. The bias could branch from patterns of genome mutation or to natural selection for translational accuracy and efficiency. Transcriptomes of 19 species of choanoflagellates are currently being used to build phylogenetic trees to elucidate the origin of different families of retrotransposons. Codon bias has also been studied to clarify the evolutionary pressures on pol genes. The study of retrotransposons in a broad range of choanoflagellates currently available will be complemented with new genomic sequencing of retrotransposons in full length using nanopore technology, supporting a thorough study of these elements to clarify their role in the evolution of protists.
2019 International Choanoflagellates & Friends Meeting Page 33 of 38
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Structural Analysis of Diverse Microbial Sulfonolipids, Molecules which Induce Morphogenesis in the Marine Eukaryote Salpingoeca rosetta
C.-C. Peng,1 L. Raguž,1 T. Jautzus, 1 E. Ireland,2 N. King,2 C. Beemelmanns1 1 Chemical Biology of Microbe-Host Interactions, Hans-Knöll-Institute (HKI), Beutenbergstrasse 11a, 07745 Jena 2 Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA.
The choanoflagellate Salpingoeca rosetta, one of the closet living relatives of animals, has become a model system to study the evolution of multicellularity. Previous studies showed that the morphogenesis of S. rosetta from a single cell into multicellular rosette-shape colonies “rosettes” is regulated by rosette-inducing factors (RIFs), an unusal group of sulfonosphingolipids. These sulfonosphingolipids are produced by Gram-negative Bacteroidetes bacterium, Algoriphagus machipongonensis.1, 2 Moreover, A. machipongonensis also produced another morphorgenetic factor - inhibitor of rosettes (IOR) to regulate the rosettes formation (Figure 1).3 However, the complex chemical ecology and structure-activity relationship (SAR) between S. rosetta and these small molecules is poorly explored. We aim to understand how RIFs, IOR and naturally occurring analogs influence rosette-induction assays,4 and eventually provide chemical probes for conducting target identification and mechanistic studies.
Figure 1. Morphogenesis of the choanoflagellate S. rosetta upon exposure to the prey bacterium A. machipongonensis
1. C. Beemelmanns, A. Woznica, R. A. Alegado, A. M. Cantley, N. King, J. Clardy, J. Am. Chem. Soc. 2014, 136, 10210-10213. 2. A. Woznica, A. M. Cantley, C. Beemelmanns, E. Freinkman, J. Clardy, N. King, Proc. Nat. Acad. Sci USA. 2016, 113, 7894-7899. 3. M. Cantley, A. Woznica, C. Beemelmanns, N. King, J. Clardy, J. Am. Chem. Soc. 2016, 138, 4326-4329. 4. R. A. Alegado, L. W. Brown, S. Cao, R. K. Dermenjian, R. Zuzow, S. R. Fairclough, J. Clardy, eLife, 2012, e00013.
2019 International Choanoflagellates & Friends Meeting Page 34 of 38
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Can we induce tumor-like growth in Choanoflagellates?
Anna Neuerburg, Hai-Kun Liu Division of Molecular Neurogenetics, German Cancer Research Center (DKFZ), Im Neuenheimer Feld 581, 69120 Heidelberg, Germany
A tumor is a very complex and heterogeneous colony of cells that arises from different driver- and passenger- mutations of cell communication and growth control genes. Lately, the genes coding for (tumor-) pathway proteins have been found to be present in Choanoflagellates, the sister group to metazoans and one of their closest living single-celled relatives. Since Chonanoflagellates are considered to be a good model organism to study the development of a multicellular organism from one single cell we want to induce a tumor-like growth in a Choanoflagellate colony. Our aim is to create a “down to the roots” tumor model organism that can help us understand the development of tumor like growth on a very basic level.
2019 International Choanoflagellates & Friends Meeting Page 35 of 38
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Transcriptional regulation of the choanoflagellate theca: implications for the origin of animal cell types
Max Coyle Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA
In every animal, distinct cell types perform specialized roles, yet we have little insight into the evolutionary trajectory that led from unicellular life to this incredible collaboration of specialized cells. More specifically, how the nature and evolution of transcriptional networks influenced the origin of animal cell types is poorly understood. This is partially due to the limited phylogenetic diversity of taxa in which the transcriptional regulation of cell types has been studied. Using the choanoflagellate Salpingoeca rosetta to expand these studies to the closest extant animal relatives, I have begun to unravel the transcriptional mechanism behind a cell type transition in choanoflagellates, that of free-swimming cells to thecate cells, which attach to a substrate through a secreted stalk of extracellular matrix. Using RNA-sequencing to catalog cell-type specific transcriptomes, I have tested candidate regulatory transcription factors (TFs) and identified a master regulatory TF that is sufficient to implement the thecate cell type. Orthogonal bioinformatic work has led to the discovery of a motif significantly enriched in the promoters of thecate-activated genes. Through the unraveling of this network, I question how the structure of pre-animal transcriptional networks may have facilitated the origin of cell types on the animal stem lineage. I attempt to reconcile this data with theoretical models of animal cell type origins.
2019 International Choanoflagellates & Friends Meeting Page 36 of 38
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Choanoflagellate Kinase Chemical Genetics
Florentine Rutaganira, Nicole King Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA
Although all organisms use signal transduction to respond to external stimuli, the rise of multicellularity necessitated the evolution of signaling pathways to coordinate actions of individual cells into a singular response. Tyrosine kinase (TK) signaling, characterized by reversible phosphorylation on tyrosine residues by TKs and phosphatases, has profound effects on animal cell growth, proliferation, and migration. Choanoflagellates, the closest living relatives of animals express an expanded set of TK signaling domains, suggesting that a functional TK signaling system evolved before the origin of animals. Multiple choanoflagellate species, including Salpingoeca rosetta, differentiate into solitary and colonial forms. Recent advances in kinase (including TK) inhibitor profiling and phosphoproteomics provide complementary chemical genetic approaches to genetic tools for identifying and elucidating how kinase, and specifically TK signaling, influences choanoflagellate development. Because TK signaling is conserved between choanoflagellates and animals, studying TK signaling in choanoflagellates can reveal whether TK signaling facilitates multicellular transitions that predate the evolution of obligate multicellularity in the animal stem lineage and inform our understanding of modern animal development, physiology and disease.
2019 International Choanoflagellates & Friends Meeting Page 37 of 38
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Confinement induces a switch to an amoeboid phenotype in choanoflagellates
Thibaut Brunet Department of Molecular and Cell Biology, UC Berkeley, Berkeley, CA 94720, USA
Amoeboid cells – that crawl by overall, actomyosin-mediated deformation of the cell body – are widely present in holozoans, and one of the fundamental animal cell types. However, the origin of animal contractile cell types remains obscure. One intriguing point is the absence of amoeboid cell types from choanoflagellates, the sister-group of animals, which has been speculated to reflect secondary loss. Here, I report on the recent discovery that the ability to differentiate into an amoeboid form is latent in choanoflagellates. Under confinement, the model choanoflagellate Salpingoeca rosetta rapidly undergoes a phenotypic switch from a flagellate to an amoeboid cell phenotype that resemble animal migratory cells in both structure and function. These observations has been generalized to other choanoflagellates. This dramatically extends the known phenotypic repertoire of choanoflagellates and suggests an ancient origin for animal crawling cells, in line with the temporal-to-spatial transition hypothesis for the origin of animal cell types.
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