Speaker: Michelle Thayer, graduate student in McGrail Lab

Major: Molecular, Cellular and Developmental Biology

Major professor: GDCB Associate Professor Maura McGrail

Department: Genetics, Development and Cell Biology

Title: "Rbbp4 requirement in shaping the epigenomic global landscape during neural progenitor proliferation and differentiation"

Abstract: The retinoblastoma binding protein 4 (RBBP4) is a conserved histone chaperone protein within epigenetic gene regulatory complexes. Rbbp4 is highly enriched in tissues within the early germ cell layers and the CNS throughout embryonic development. Diseases arise when the epigenetic environment is not properly established and maintained in early development. An example of this is the manifestation of pediatric brain cancers which are often linked to the dysregulation of global histone modifications regulated by Rbbp4-containing protein complexes. Although, the mechanistic importance of Rbbp4 during normal embryonic neurogenesis is largely unknown. This research aims to investigate three Rbbp4-dependent mechanisms which may regulate embryonic brain development. First, Rbbp4 role in the survival, proliferation, and differentiation of neural progenitor cells through regulating cell cycle exit and activation of the tumor suppressor, apoptosis-inducing protein, TP53. Our findings using rbbp4 mutant zebrafish show a reduction in deacetylation of p53 causing cell death in the retina and tectum and upon tp53 deletion, there is an increase in mitotic cells. Second, exploring the mechanistic role of Rbbp4 through its association with the DREAM complex. DREAM-RBBP4 complex may guide or associate with H3K9 methyltransferases to/at transcription start sites to regulate the gene transcription of late cell cycle genes FoxM1 and PLK1 in neural progenitor cells. Immunolocalization assay depicts a marked loss of H3K9me2/3 in rbbp4 mutant and an increase in mRNA expression of DREAM-regulated genes FoxM1 and PLK1 in rbbp4 mutants. Concordantly, inhibiting FoxM1 in early rbbp4/tp53 mutants shows a reduction in mitotic cells. Finally, we address Rbbp4s contribution in the PRC2-EZH2 methyltransferase complex in regulating H3K27me3 deposition during brain development and regulation of WNT/B-catenin activation. Our results analyzing H3K27me3, and B-catenin-Rbbp4-dependent interactions indicate a disruption in H3K27me3 histone deposition and a possible unique protein isoform of B-catenin along with an increase in B-catenin mRNA transcript levels in the rbbp4 mutants. Moreover, Neruod1cre; rbbp4on/4 mutant embryos demonstrate Rbbp4 may play a cell-autonomous role in WNT/B-catenin signaling in Neruod1 expressing cells in the neural retina and mesencephalon. Our preliminary research signifies the importance of Rbbp4 in modulating the chromatin landscape during neural progenitor cell fate decisions of survival, proliferation, and differentiation likely through DREAM, PRC2, WNT/B-catenin, and HDAC complexes. This research contributes mechanistic insight into the in vivo epigenetic environment during embryonic neurogenesis and how when dysregulated could lead to tumorigenesis.