Drosophila HP1c isoform interacts with the zinc-finger proteins WOC and Relative-of-WOC to regulate gene expression

Abstract

Heterochromatin protein 1 (HP1) proteins are conserved in eukaryotes, with most species containing several isoforms. Based on the properties of Drosophila HP1a, it was proposed that HP1s bind H3K9me2,3 and recruit factors involved in heterochromatin assembly and silencing. Yet, it is unclear whether this general picture applies to all HP1 isoforms and functional contexts. Here, we report that Drosophila HP1c regulates gene expression, as (1) it localizes to active chromatin domains, where it extensively colocalizes with the poised form of RNApolymerase II (RNApol II), Pol IIo ser5 , and H3K4me3, suggesting a contribution to transcriptional regulation; (2) its targeting to a reporter gene does not induce silencing but, on the contrary, increases its expression, and (3) it interacts with the zinc-finger proteins WOC (without children) and Relative-of-WOC (ROW), which are putative transcription factors. Here, we also show that, although HP1c efficiently binds H3K9me2,3 in vitro, its binding to chromatin strictly depends on both WOC and ROW. Moreover, expression profiling indicates that HP1c, WOC, and ROW regulate a common gene expression program that, in part, is executed in the context of the nervous system. From this study, which unveils the essential contribution of DNA-binding proteins to HP1c functionality and recruitment, HP1 proteins emerge as an increasingly diverse family of chromatin regulators.[Keywords: HP1; WOC; ROW/CG8092; chromatin; Drosophila] Supplemental material is available at http://www.genesdev.org.

dDsk2 regulates H2Bub1 and RNA polymerase II pausing at dHP1c complex target genes

“…We and others previously reported that dHP1c interacts with the transcription factors WOC and ROW 17,18 . Here to identify partners of the dHP1c complex, we performed affinity purifications using stable S2 cell lines expressing ROW-TAP and TAP-WOC fused proteins.…”

“…5c). On the other hand, binding of the dHP1c complex likely involves the recognition of specific DNA sequences since it depends on the zinc-finger proteins WOC and ROW 18 ( Supplementary Fig. 3a,b).…”

“…dDsk2 is highly evolutionarily conserved from yeast to humans 10,15,16 . We show that, in addition to regulating protein stability, Drosophila dDsk2 interacts with the complex formed by the euchromatic dHP1c isoform and the transcription factors WOC and ROW [17][18][19] , localizes at promoters and is required for transcription via nonproteolytic mechanisms.…”

“…Altogether, these results suggest that, although the interaction of dDsk2 with H2Bub1 is important for transcription and stabilizes binding of the complex, it is not essential for its recruitment to promoters. In this regard, the zinc-finger proteins WOC and ROW mediate binding of both dHP1c 18 and dDsk2 ( Supplementary Fig. 3a,b), suggesting that they play a crucial role in recruitment.…”

“…The dHP1c complex was shown to localize at active chromatin domains, suggesting a role in gene expression regulation 17,18 . However, its actual genomic distribution and the extent of overlapping of its components were not known.…”