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Evolution of the Complex Eye and Pax6 Gene

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Evolution of the Complex Eye and Pax6 Gene 3/13/13 Evolution of the Complex Eye and Pax6 Gene Rachel Thomsen Sarah Kim Jenia Ostrovskaya Key Points • Definition of an Eye o Types of Eyes • Origin of Species: Difficulties on Theory • Pax family • Pax6 gene why it is conserved? • Experiments o Fruit flies, mice and humans missing Pax6 o Misexpression of genes in flies using Pax6 genes from mice • DNA sequencing leads to new phylogenetic tree proposal • Co-option (Crystallins and Shielding Pigment) • Planarian Experiment, exception to the Pax6? 1 3/13/13 What is an “eye”? • Organ of vision or light sensitivity (Medical Dictionary) • Types of Eyes o Simple § Light sensing o Complex § Image forming http://learn.genetics.utah.edu/content/variation/toolkit/ Origin of Species Chapter IV: Difficulties on Theory - The Eye "To suppose that the eye, with all its inimitable contrivances for adjusting the focus to different distances, for admitting different amounts of light, and for the correction of spherical and chromatic aberration, could have been formed by natural selection, seems, I freely confess, absurd in the highest possible degree. Yet reason tells me..." http://www.guardian.co.uk/science/2008/feb/09/darwin.eye image: http://2.bp.blogspot.com/-XtKaxmzR3zk/TkOCrFDhteI/AAAAAAAAEDs/ rr_Yo6RygG4/s640/darwin.jpg 2 3/13/13 Eyes evolved up to 65 times? · (Treisman, 2004) Polyphyletic Idea of Complex Eye Evolution Explained by Differences: • morphology • photoreceptor type usage • lens composition http://www.sciencedirect.com/science/ article/pii/S0012160609008835 3 3/13/13 PAX Genes The PAX gene family plays a critical role in the formation of tissues and organs during embryonic development. 9 genes in the PAX gene family - PAX group 1 (Pax 1 and 9) - PAX group 2 (Pax 2, 5, and 8) - PAX group 3 (Pax 3 and 7) - PAX group 4 (Pax 4 and 6) http://kozmik.img.cas.cz/paxgenes.html 4 3/13/13 Pax 6 Gene and Eye Development Pax 6 - "universal master control gene", especially for eye morphogenesis. It represents a master switch initiating a cascade of at least 2,000 genes which are required for eye morphogenesis. http://evolution.berkeley.edu/evolibrary/article/1_0_0/eyes_10 5 3/13/13 Evolution of Eyes - A Just-So Story? Eyes evolved by a mechanism called 'intercalary evolution'. Intercalary evolution is that in the evolution of eyes various already-existing genes were recruited in different lineages at different stages of eye development between induction by PAX 6 at the top, and photoreceptor differentiation at the bottom of the cascade. Studies of Pax6 gene http://www.plosbiology.org/article/info%3Adoi%2F10.1371%2Fjournal.pbio.1000247 6 3/13/13 Pax6 Gene Experiment Figure.Targeted expression of the Pax6 gene in a Drosophila non- eye imaginal disc. (A) A strain of Drosophila was constructed wherein the gene for the yeast GAL4 transcription factor was placed downstream from an enhancer sequence that normally stimulates gene expression in the imaginal discs for mouthparts. If the embryo also contains a transgene that places GAL4-binding sites upstream of the Pax6 gene, the Pax6 gene will be expressed in whichever imaginal disc the GAL4 protein is made. (B) Drosophila ommatidia (compound eyes) emerging from the mouthparts of a fruit fly in which the Pax6 gene was expressed in the labial (jaw) discs. (Photograph courtesy of W. Gehring and G. Halder.) http://9e.devbio.com/image.php?id=566 CO-OPTION: "Old Genes, New Tricks" • Crystallins and Pax Proteins http://learn.genetics.utah.edu/content/variation/toolkit/ 7 3/13/13 New Monophyletic Tree Proposal Network of genes (Pax6) is conserved Supports Darwinian Prototype Eye proposal (Gehring, 2005) Planaria! http://www.shippokudo. com/c.planaria.jpg http://cdn.c.photoshelter.com/img-get/I0000apagS.7JpiQ/s/ 860/860/20120430-planaria-live-IMG-4500.jpg 8 3/13/13 Planarians an exception to new theory of eye evolution? • Planaria injected with a Pax6 inhibitor (RNAi) • Stained to show cephalic brain formation • No difference in regeneration of eye spots and cephalic ganglia pattern. (Pineda, 2002) http://askapsychicfree.com/f/Psychics- Questions-and-Answers.jpg 9 3/13/13 Literature Cited Erclik Ted, Volker Hartenstein, Roderick R. McInnes, and Howard D. Lipshitz. "Eye Evolution at High Resolution: The Neuron as a Unit of Homology." Developmental Biology 332.1 (2009): 70-79. Print. Favor J, Gloeckner C. J, Neuhauser-Klaus A, Pretsch W, Sandulache R, et al. (2008) Relationship of Pax6 activity levels to the extent of eye development in the mouse, Mus musculus. Genetics 179: 1345–1355. Gehring W. J. 2005. New perspectives on eye development and the evolution of eyes and photoreceptors J. Heredity, 96: 171–184 Halder G, Callaerts P, Gehring W. 1995. Induction of Ectopic Eyes by Targeted Expression of the Eyeless Gene in Drosophila. Science. 267: 1788-1792. Literature Cited (cont.) Pineda David, Rossi Leonardo, and Batistoni Renata, et al. "The Genetic Network of Prototypic Planarian Eye Regeneration Is Pax6 Independent." Company of Biologists Limited129 (2002): 1423-434. Print. Singh A. 2009. Drosophila ey−/−. Dayton, OH: Department of Biology, University of Dayton. Sisodiya SM, Free SL, Williamson KA, Mitchell TN, Willis C, et al. (2001) PAX6 haploinsufficiency causes cerebral malformation and olfactory dysfunction in humans. Nat Genet 28: 214–216 Treisman J.E. 2004. How to make an eye. Development. 131: 3823–3827 Washington NL, Haendel MA, Mungall CJ, Ashburner M, Westerfield M, Lewis SE. Linking human diseases to animal models using ontology-based phenotype annotation. PLoS Biol. 2009;7(11):e1000247. 10 .
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