View Program - 63rd Annual Drosophila Research Conference

During metazoan development, gene regulatory networks (GRNs) are activated in undifferentiated tissues to induce a specific fate. However, when GRNs are disrupted, the tissue can transdetermine – losing the programmed fate to adopt another. Epigenetic factors, such as the Polycomb Group (PcG) proteins, ensure proper spatiotemporal control of GRNs. PcG proteins function as a set of complexes to add a repressive histone mark (H3K27me3) and condense chromatin. In turn, the accessibility of chromatin – or lack thereof – regulates differential transcription of genes in certain tissues. While the correlation between GRNs and chromatin modifications in development is widely established, the underlying mechanisms linking the two during transdetermination has yet to be discovered. The overarching goal of this project is to determine how epigenetic modifications affect tissue fate specification. An excellent model to study the mechanisms underlying fate plasticity is the eye-to-wing transformation of Drosophila eye-antennal discs (EADs). Previous work from our lab discovered that the EAD-specific removal of one PcG protein, Polycomb (Pc), transforms the eye imaginal tissue to wing – indicating that the loss of epigenetic repression is sufficient to allow cellular reprogramming.
To investigate the molecular mechanism underlying this transformation, I have performed RNA-seq on wild-type (WT) wing discs (WDs) as well as WT and Pc mutant EADs throughout third instar development. This analysis identified 55 candidate genes that could be responsible for promoting reprogramming of the EAD. My preliminary data suggest the most promising of these candidates is vestigial (vg), as this locus is directly regulated by Pc. Furthermore, overexpression of vg in the EAD grants an eye-to-wing transformation, and ectopic vg expression is detected in the developing wing pouch of the transformed disc. I will further investigate how repressive and active histone modifications are changing in this system to allow for reprogramming by using a novel epigenome profiling technique, CUT&RUN. I hypothesize that the inability of Pc mutants to read H3K27me3 marks allows the epigenome to become malleable, activates wing determination genes, and transforms the eye into a wing. Outcomes of this study will elucidate the mechanistic role epigenetic factors play in tissue fate determination, ultimately providing insight into how mutations in epigenetic proteins result in human developmental disorders.

Investigating the role of Polycomb repression in Drosophila eye specification

**Investigating the role of Polycomb repression in Drosophila eye specification**