Unraveling the gene regulatory network specifying urbilaterian photoreceptors - a comparative study between Branchiostoma (Chordata) and Platynereis (Annelida)

• Applicant: Professor Dr. Detlev Arendt
• Subject Area: Evolution, Anthropology
• Term: from 2010 to 2014
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 165401976

The molecular analysis of eye development in mice and fly has revealed stunning similarities (such as the conserved role of Pax6) but also uncovered important differences in the set of transcription factors involved (for example, Rx playing a crucial role in the vertebrates but not in insects). We hypothesize that these differences reflect the differential deployment of two types of light-sensitive (photoreceptor) cells, ciliary and rhabdomeric . Both co-exist in many bilaterian animal groups; however vertebrates have recruited the ciliary and invertebrates the rhabdomeric type for vision. Hence, we propose to investigate the function of ciliary and/or rhabdomeric photoreceptor-specific transcription factors such as Rx, Prox, Otx, Six 12 and Lhx2 in eye and photoreceptor cell specification in the slow-evolving marine annelid Platynereis dumerilii. In this emerging molecular model species, both types of photoreceptor cells differentiate early and eye development is fully accessible from early larval stages onwards. In a collaborative effort with the laboratory of Zbynek Kozmik in Prague, Czech Republic, we will determine the genes directly regulated by these transcription factors by chromatin immunoprecipitation combined with second generation sequencing (ChiP-seq). The effect on putative targets will be validated and characterized by the morpholino knockdown technique recently established for Platynereis and/or by Zinc finger nuclease-mediated gene knockout followed by qPCR and in situ hybridisation analysis. Also, we will determine the cell type-specific expression of validated candidate genes by Wholemount In Silico Expression Profiling, another protocol recently developed in the Arendt laboratory that allows expression profiling in cellular resolution. Subsequently, our data will be compared with similar data obtained for the chordate amphioxus, another slow evolving marine molecular model with both ciliary and rhabdomeric photoreceptor cells. This way we aim at unravelling the conserved core of the photoreceptor-specific gene regulatory network in Bilateria as a starting point to understand similarities and differences in vertebrate versus invertebrate eye development.

• DFG Programme: Research Grants
• International Connection: Czech Republic
• Participating Person: Dr. Zbynek Kozmik