The Role of PRC1 and the SAGA-DUB Complex in the Developmental Genes of Zebrafish

Bhachech, Liam, B / Eckerd College

Abstract:

In vertebrates, gene activation or silencing typically requires permissive histone modifications and localized DNA hypomethylation. Key permissive histone modifications included H3K4 methylation and H3 acetylation, while H3K27me3 focal hypomethylation was a prominent gene silencing marker deposited by Polycomb Repressive Complex 2 (PRC2). These modifications call in PRC1 to then ubiquitinate histones H2A and H2B. H2A monoubiquitination (H2Aub1) led to gene suppression, and H2Bub1 promoted gene activation. Interestingly, zebrafish exhibited these permissive histone modifications relatively late during embryonic development, specifically at Zygotic Genome Activation (ZGA). Notably, H2Aub1 and Rnf1 were present in developmental gene promoters during Pre-ZGA, suggesting that PRC1 acts non-canonically and potentially promiscuously. This raised questions about how developmental genes were activated in zebrafish. We hypothesized that deubiquitination complexes, such as BAP1 and the SAGA-DUB complex, regulate the ubiquitination levels of developmental genes, thereby influencing developmental gene expression. To investigate this, we applied a USP22-specific deubiquitinase inhibitor (the deubiquitinase protein in SAGA-DUB), Morusin, to zebrafish embryos across various doses in multiple six-well plate experiments. We observed phenotypic changes, particularly in tail development, potentially linked to hox gene 13, alongside preserved H2Aub1 in pre-ZGA and ZGA stages. Additionally, H2Bub1 was maintained in 24-hour post-fertilization embryos, with consistent methylation patterns observed in treated specimens. These findings suggested that deubiquitination complexes play a major part in developmental gene regulation, challenging existing models of gene expression during early embryonic development in zebrafish.

Acknowledgment – This work was supported by the Huntsman Cancer Institute at the University of Utah, an HHMI affiliate