The Dm-Myb Oncoprotein Contributes to Insulator Function and Stabilizes Repressive H3K27me3 PcG Domains

Juan F Santana,Mrutyunjaya Parida,Abby Long,Joshua Wankum,Anthony J Lilienthal,Krishna M Nukala,J Robert Manak

doi:10.1016/j.celrep.2020.02.053

Abstract

SUMMARYDrosophila Myb (Dm-Myb) encodes a protein that plays a key role in regulation of mitotic phase genes. Here, we further refine its role in the context of a developing tissue as a potentiator of gene expression required for proper RNA polymerase II (RNA Pol II) function and efficient H3K4 methylation at promoters. In contrast to its role in gene activation, Myb is also required for repression of many genes, although no specific mechanism for this role has been proposed. We now reveal a critical role for Myb in contributing to insulator function, in part by promoting binding of insulator proteins BEAF-32 and CP190 and stabilizing H3K27me3 Polycomb-group (PcG) domains. In the absence of Myb, H3K27me3 is markedly reduced throughout the genome, leading to H3K4me3 spreading and gene derepression. Finally, Myb is enriched at boundaries that demarcate chromatin environments, including chromatin loop anchors. These results reveal functions of Myb that extend beyond transcriptional regulation.

Highlights

Vertebrates contain three representatives of the Myb gene family, consisting of A, B, and c-Myb, all of which encode transcription factors important for the proper expression of large numbers of genes (Rushton et al, 2003)
Drosophila dREAM plays a pivotal role in regulating proper expression of genes associated with the G2/M transition, and its absence leads to chromosomal instability and an increase in the mitotic index (Fung et al, 2002; Georlette et al, 2007; Manak et al, 2002; Wen et al, 2008). dREAM acts largely as a repressor through E2f2, whereas Myb predominantly functions as the activating arm of the complex (Georlette et al, 2007; Jackson et al, 2001; Lewis et al, 2004)
To identify genes regulated by Myb in wing discs, we performed both gene expression microarray as well as RNA sequencing (RNA-seq) comparisons of MybMH107 null mutants with yw67 controls (Table S2), finding a strong correlation of the datasets (r = 0.89; p < 0.0001; Figure S1) for overlapping differentially expressed genes

Summary

Introduction

Vertebrates contain three representatives of the Myb gene family, consisting of A-, B-, and c-Myb, all of which encode transcription factors important for the proper expression of large numbers of genes (Rushton et al, 2003). Drosophila dREAM plays a pivotal role in regulating proper expression of genes associated with the G2/M transition, and its absence leads to chromosomal instability and an increase in the mitotic index (Fung et al, 2002; Georlette et al, 2007; Manak et al, 2002; Wen et al, 2008). All components of the complex are present at the majority of target promoters (Georlette et al, 2007), and the absence of both Myb and E2f2 causes variegated expression of a variety of genes (Wen et al, 2008). Several studies have implicated Myb as an epigenetic regulator of gene transcription (Bohla et al, 2014; Korenjak et al, 2014; Sim et al, 2012; Wen et al, 2008); no clear evidence exists regarding specific mechanisms by which this epigenetic regulation is achieved

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