Bill Gillis
wgillis@uoregon.edu
University of Oregon
Department of Biology
1210 University of Oregon
Eugene, OR 97403
Advisors: Stephan Schneider and Bruce Bowerman
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Using Polychaetes to decipher the evolution of the mesodermal genetic toolkit
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From a worm to a human, the regulation of early embryonic patterning is controlled by a limited set of common gene families. The wide conservation of this 'genetic toolkit' suggests that it must have been present in the last common ancestor of protostome and deuterostome animals, the so-called urbilaterian. However, the number of genes in each gene family varies significantly between animals. This is due to the frequent duplication and loss of genes in many branches of the tree of life, and can complicate our comparative analyses of these homologs. I use phylogenetic inference to explore how the evolution of a gene family, including changes in both gene number and sequence, correspond to its expanding roles in germ and tissue layer patterning. I have been characterizing key gene families within a marine annelid, the polychaete Platynereis dumerilii. Platynereis displays slow-evolving morphological and molecular characters, and its placement within the lophotrochozoan sub-phylum makes it an ideal link for comparative analysis between vertebrate and invertebrate model systems. I am using a wide range of molecular biology techniques (including PCR, cloning, in situ hybridization, and immunohistochemistry) to isolate and characterize Platynereis homologs.
My focus is on gene families involved in the formation of mesoderm. The invention of mesoderm is thought to have contributed to the wide diversity of body plans seen in tripoloblastic (three-layered) versus diploblastic (two-layered) animals. Mesoderm gives rise a variety of tissue types, including muscular progenitors, and allows for a coelom, a fluid-fillled cavity which protects the inner organs from the outer body wall. Curiously, homologs for mesoderm specification genes are conserved even in animals lacking mesoderm (cnidarians). This can be interpreted that these genes have either a novel role in mesoderm function (neofunctionalization) or that cnidarians might have had a secondary loss of mesoderm. My working hypothesis has been that the changes in the gene number of many of these families may provide the basis for this innovation.
My initial results in the GATA family of transcription factors suggest that a gene duplication event may be related to the invention of the mesodermal germ layer. We have found two Platynereis GATA factors, only one of which is expressed in the developing mesoderm. A phylogenetic analysis supports that these two homologs appear to represent the full bilaterian complement of GATA factors, while only a sole cnidarian GATA can be identified. Indeed a comparative review of GATA expression and function show that like Platynereis, all bilaterian GATAs can be shown to be derived from these two ancestral bilaterian GATAs, with only one class involved in the early specification of mesoderm. This suggests that mesoderm evolved concurrently with the duplication of the GATA factors, and that only one duplicate was co-opted in the early specification of mesoderm.
(Green: TOPRO-3 nuclear counterstain)
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Publications & Posters
• S. Khan, R. Makkena, F. McGeary, K. Decker, W. Gillis, and C.J. Schmidt. (2003) A Multi-Agent System for the Quantitive Simulation of Biological Networks. In Proceedings of the International Conference on Autonomous Agents and Multi-Agent Systems, 2003.
• S. Khan, K. Decker, W. Gillis, and C.J. Schmidt.(2003) A Multi-Agent System-driven AI Planning Approach to Biological Pathway Discovery. In Proceedings of the International Conference on Automated Planning, 2003.
• Gillis W.J., Bowerman B.A., Schneider S.Q. (2005, March) The GATA family of Transcription Factors within the polychaete Platyneries dumerilii. W.J. Gillis, B.A. Poster Presented at the Northwest Regional meeting of the Society of Developmental Biologists, Friday Harbor, Washington.• Gillis W.J., Bowerman B.A., Schneider S.Q. (2005, July) The GATA family of Transcription Factors within the polychaete Platyneries dumerilii. W.J. Gillis, B.A. Poster Presented at the annual meeting of the Society of Developmental Biologists, San Francisco, California
• Gillis W.J., Bowerman B.A., Schneider S.Q. (2006, March) Expression domains of two highly conserved GATA factors in Platynereis dumerilii elucidate an ancestral bilaterian split between neuroectodermal and mesodermal subfunctions. Talk Presented at the Northwest Regional meeting of the Society of Developmental Biologists, Friday Harbor, Washington.