PgmNr W4113: In search of C. elegans histone H3 lysine 27 methylation (H3K27me) ‘readers’.

Authors:
Arneet L. Saltzman 1,2 ; Mark W. Soo 1 ; Jeannie T. Lee 1,2,3


Institutes
1) Department of Molecular Biology, Massachusetts General Hospital; 2) Department of Genetics, Harvard Medical School; 3) HHMI.


Keyword: Chromatin organization

Abstract:

The Polycomb group proteins form chromatin-modifying complexes that function in the inheritance of gene expression patterns. Originally identified in Drosophila for their role in body patterning through Hox gene repression, Polycomb group proteins act in part through repressive modifications to the N-terminal tails of histones. In particular, methylation of lysine 27 on histone H3 (H3K27me) can be recognized or ‘read’ by the chromo (chromatin organization modifier) domain, found in the Drosophila Polycomb and related mammalian Chromobox proteins. Previous work has shown that H3K27me is important for germ cell fate and worm development, yet a ‘reader’ of this mark in C. elegans has remained elusive. Several C. elegans genes have been identified by the sequence similarity of their encoded chromodomains to those of Polycomb and Chromobox proteins (Agostoni et al. 1996), however the binding preferences of these chromodomain-containing factors are not known. To determine whether these candidates have specificity for methylated histone tail residues, we are using a biochemical approach in which recombinant proteins are assayed for binding to a panel of histone tail peptides. To understand the potential roles of these proteins in development and chromatin modification pathways, we are creating knockout and tagged knock-in strains that will allow us to identify the genomic binding sites and protein interaction partners of these proteins by ChIP-Seq and mass spectrometry, respectively. Our results suggest that the C. elegans genome encodes several chromodomain ‘readers’ of histone H3K27 methylation. Uncovering the degree of functional overlap versus cell type or target locus-specificity among these related factors may provide an informative model for the regulatory complexity also observed in mammalian chromatin modification readers.