11/04/17 From Nerve Net to Brain: The Rise of the Urbilaterian in Animal Evoluon Detlev Arendt 10-04-17 COS, Heidelberg University European Molecular Biology Laboratory Heidelberg, Germany Bringing the ocean to Heidelberg annelid amphioxus sea anemone sponge Man is but a worm Animal evoluon Acrania Ambulacraria Cnidaria Protostomia Placozoa the Urbilaterian Ctenophora the cnidarian-bilaterian ancestor ? Porifera the Urneuralian the last metazoan common ancestor Choanoflagellata the first animal some images courtesy C. Nielsen choanoflagellates Latest phylogenomic animal tree (Simion et al 2017) Animals emerged in the Ediacaran (Budd and Jensen 2015) Animal evoluon Acrania Ambulacraria Cnidaria Protostomia Placozoa Ctenophora ? Porifera Choanoflagellata the first animal choanoflagellates resemble sponge choanocytes Dayel.com Salpingoeca rosea Dayel.com ARTICLE IN PRESS 190 The first cell type: the 4 choanocyte 191 (a)(b) rstb.royalsocietypublishing.org 192 Plesiomorphies: 193 • guanylyl cyclase signaling via cGMP 194 • TRP channels 195 • various GPCRs including the metabotropic glutamate receptor 196 • prominent endocytoc machinery mediang phagocytosis 197 • well-developed Golgi produces lysosomes for intracellular digeson 198 199 200 201 Synapomorphies HolozoaPhil. Trans. R. Soc. B : 202 • flagellum surrounded by a collar of contracle microvilli 203 • 5 TRP channels , TRPV involved in mechanosensaon 204 • ‘synapc’ adhesion molecules 205 • a primordial neurosecretory apparatus acve on the apical cell 206 surface (but no presynapc acve zone proteins) 207 • postsynapc density proteins such as Homer or Shank 20150286 208 • actomyosin with NM- MHCII for slow contracon, integrin-mediated 209 basal adhesion, intercellular adhesion 210 • ST-MHCII for fast contracon (of what?) 211 212 213 Figure 2. The origin of metazoans. (a) The choanoblastaea. This animal represented the simplest possible(Ruiz- epitheliumTrillo in the, Burkhardt form of a sphere., King) The first and only cell 214 type are choanoflagellate-like cells. (b) A hypothetical ancestral metazoan cell-type resembling choanoflagellates. These cells had an apical, undulating cilium or Arendt et al., Phil. Trans. Roy. Soc. Lond. 2015 215 flagellum, propelling water away from the cell, surrounded by a circle of long, contractile, actin-containing microvilli. A well-developed Golgi complex produces 216 lysosomes for intracellular digestion, and a prominent endocytotic machinery mediates phagocytosis (Pc). Mm, mucoid mesh; Fp, filopodia. 217 218 Chemosensation involved guanylyl cyclases signalling via basal adhesion, cell–cell adhesion dynamics via adherens 219 cGMP (Johnson, 2010 #5539). Five subfamilies of transient junctions or apical constriction [37]—processes that were 220 receptor potential (TRP) channels were present [24], among key for the evolution of metazoan epithelia. The slow 221 which TRPV channels likely played an ancient role in mechan- myosin is also involved in amoeboid movement [38] that 222 osensation, as they mediate mechanosensation in Paramecium probably belonged to the behavioural repertoire of early 223 and Chlamydomonas [25], human airway epithelia [26] and metazoan cells. In addition, we can infer that early metazoan 224 Caenorhabditis elegans sensory cells [27]. In Chlamydomonas, cells formed lamellipodia and filopodia, using proteins that 225 these channels localize to the proximal region of the cilia, reorganize cortical actin filaments such as the Arp2/3 com- 226 where active bending is restricted (and self-activation avoided) plex, the actin cross-linking protein fascin and myosin X, a 227 [25]. Proteins required for action potential generation and myosin with pleckstrin homology domains that associates 228 propagation were likewise present in early meatzoans, such with regions of dynamic actin [39,40]. Filopodia are highly 229 as voltage-gated sodium [28,29], potassium and calcium dynamic structures that probably played a role in anchoring 230 channels [30]. Mechanical and chemical stimuli triggered and stabilizing cells in the blastaea (figure 2a,b). 231 depolarization of the ciliary membrane potential and calcium 232 influx into the cilium that had a direct effect on ciliary beat- 233 ing such as reversal or inhibition, as reported for unicellular 234 eukaryotes, cnidarians, ctenophores and bilaterians [31]. 3. The microphageous gastraea 235 Adding to this, choanoflagellates and metazoans share It is a long-standing notion that the second step in the evolution 236 synaptic adhesion/signalling molecules, a primordial neuro- of the metazoan body was the transformation of the spherical 237 secretory apparatus active on the apical cell surface (but no blastaea into the gastraea [9,10], which may have been close to 238 presynaptic active zone proteins) [32], postsynaptic density the last metazoan common ancestor (figure 1b). The term ‘gas- 239 proteins such as Homer or Shank [33,34] and a variety of recep- traea’ means ‘animal with a primitive gut’ and was coined by 240 tors including the metabotropic glutamate receptor [35] (but Ernst Haeckel [10]. Its most characteristic feature is the infolding 241 not ionotropic glutamate receptors, which only appeared in of the lower body surface, resulting in an outer ectoderm, 242 the metazoan stem). Many of these molecules and associated an inner gastroderm and a gastric opening (figure 3a). From 243 functions were key to the evolution of the first neural cell Haeckel’s times until today, strong support for the gastraea 244 types, as will be detailed below. hypothesis comes from the prevalence of gastrula-like stages 245 On the effector side, early metazoans cells already pos- during animal development that are interpreted as recapitula- 246 sessed a complex machinery for cellular contractions and tion of the gastraea-like ancestral body plan. Even in sponges, 247 shape changes based on a dynamic actomyosin cytoskeleton. a transitory cup-like stage forms during metamorphosis, as 248 Actin-based movement involved a slow and a fast version of recently confirmed [41]; and in cnidarians and ctenophores, 249 myosin II that responded in a different manner and with the overall body form resembles that of a gastrula during the 250 different velocities to Ca2 signalling [36]. The slow non- entire life cycle—at larval, polyp and medusa stages. The þ 251 muscle myosin probably played a role in various cellular ancient gastraea is originally assumed as creeping on the sea 252 processes involving contraction, such as integrin-mediated floor, with the gastric opening facing downwards (while other RSTB20150286—6/10/15—21:35–Copy Edited by: Not Mentioned The first animals possessed large part of the pre- and postsynapc cellular modules (Liebeskind et al 2017) Kolmer-Agduhr cells ‘protoneuron’ chemosensory cell enterocyte choanocyte- like precursor mechanosensory hair cell rhabdomeric photoreceptor flame cell Animal evoluon Acrania Ambulacraria Cnidaria Protostomia Placozoa Ctenophora ? Porifera Choanoflagellata the first animal Animal evoluon Acrania Ambulacraria Cnidaria Protostomia Placozoa Ctenophora ? Porifera the last metazoan Choanoflagellata common ancestor The evoluon of development Arendt et al., Phil. Trans. Roy. Soc. Lond. 2015 Sponges Sponge development: GATA expression demarcates micromeres / inner cells GATA Sycon ciliatum (Calcarea) GATA Leininger et al 2014 Leininger et al 2014 Arendt et al., Phil. Trans. Roy. Soc. Lond. 2015 GATA is a marker for the inner layer in Nematostella! Mesodermal gene expression in a diploblast 2467 sea anemone Nematostella Fig. 4. Nv-GATA. Phylogenetic analysis and expression. (A) Alignment of 80 amino acids from various(Marndale et al 2004) GATA transcription factors spanning a central C2C2 zinc finger motif. (B) Phylogeny of GATA sequences. The tree was constructed and labeled as in Fig. 3. Sequences included in the analysis are: CG10278-PA (hypothetical protein), Drosophila, residues 514-595; GATA, Nematostella, residues 248-321; GATA-1 (GATA binding protein 1), Homo, residues 235-316; GATA-2, Homo, residues 326-406; GATA-3, Homo, residues 294-373; GATA-4, Homo, residues 193-273; GATA-5, Homo, residues 221-300; GATA-6, Homo, residues 274-356; grain, Drosophila, residues 292-378; MGC2306 (hypothetical protein), Homo, residues 326-407; pannier, Drosophila, residues 148-224; serpent, Drosophila, residues 451-535; TRPS1, Homo, residues 873- 959. (C-H) Expression of Nv-GATA. (C,D) Scattered cells express Nv-GATA at the blastula stage. Nv-GATA-expressing cells appear to move into the blastocoel (arrows). (E,F) At gastrulae stages expression is confined to endodermal cells. In the late planula (G) and early polyp (F) stages, ectodermal cells at the base of the developing tentacles also express Nv-GATA. Asterisks indicate the site of the mouth. end, endoderm; ect, ectoderm; tn, tentacles. 285 amino acids long. Within the forkhead domain, the 3I,J). This expression in a terminal gut structure is reminiscent Nematostella sequence is roughly 90% identical to Drosophila of the hindgut and foregut expression of forkhead in Drosophila forkhead and the FOXA2 sequence of humans (Fig. 3A). (Weigel et al., 1989) and the hypostomal expression of budhead Phylogenetic analysis places Nv-forkhead squarely within the in Hydra (Martinez et al., 1997). However, budhead is larger forkhead clade, most closely related to Drosophila expressed in the endoderm while Nv-forkhead is expressed forkhead, FOXA2, and the Hydra budhead genes (Fig. 3B). primarily in the ectodermal lining of the pharynx. The Similar to budhead