Uncovering evolutionary developmental constraints on the conserved nematode Bauplan.

• Applicant: Dr. Philipp Schiffer
• Subject Area: Evolutionary Cell and Developmental Biology (Zoology)
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 434028868

Animal phyla are recognised as distinct entities through their unique Baupläne laid out during embryonic development. The bilaterally symmetrical animal phyla are of a similar age, but show enormous difference in their morphological disparity. Perhaps the most striking example is a comparison of the highly disparate Arthropoda - containing butterflies and spiders and tardigrades and trilobites - and the hyper conserved vermiform body plan of the nematodes. This conservation is particularly astounding as the nematodes are ecologically at least as widespread and as successful as the insects, and have diversified into 1 million or more species. Which factors might underly the strict conservation of the nematode Bauplan? Here, I propose several interconnected genomic, transcriptomic, and molecular genetic approaches to study the possible link between developmental constraints and this strong conservation.Recent studies of gene expression in the model nematode Caenorhabditis elegans have supported the idea of a constrained mid developmental period. These data show that gene expression is variable early in development, then becomes more and more constrained, and subsequently becomes variable again, resembling the shape of an hourglass. This is contrasted by my own results: comparing C. elegans to 2 other nematodes, I found a funnel shaped progression of gene expression variance, seeming to provide a possible mechanism for the convergence on the conserved adult Bauplan. While I have expanded our knowledge beyond the C.elegans, it is still far from clear which of these models is the correct of developmental progression. In fact, my own data even suggest that many genes important in C. elegans development are absent in other nematode species. Overall, there is a great lack of knowledge concerning the genetics of nematode development and it remains unclear which factors enforce the phylum wide conservation of the adult vermiform Bauplan.In my project, I will analyse the genomes of drastically under-sampled early branching nematodes. Next I will study which parts of the C. elegans developmental toolkit are conserved and which vary throughout the phylum. These data will inform us when and how the derived developmental programme of C. elegans evolved along the nematode tree, and how much of the ancestral bilaterian developmental toolkit is retained in early branching nematodes. I will then study gene expression in early blastomeres (single-cells) and throughout development in time-course assays. Lastly, I will implement knockout methods to functionally characterise genes acting in gene regulatory networks of development in early branching nematodes. In summary, this will tell us how variable (or evolvable) early stages of development are on the genetic level and show whether the canonical hourglass model of development is correct, or whether a funnel like model has a better fit to explain the constrained Bauplan disparity in Nematoda.

• DFG Programme: Independent Junior Research Groups