Abstract
CHD1 is a SNF2-related ATPase that is required for the genome-wide incorporation of variant histone H3.3 in the paternal pronucleus as well as in transcriptionally active nuclei in Drosophila embryos. The S. pombe and vertebrate orthologs of CHD1 have been implicated in the assembly of the centromeric histone H3 variant CenH3CENP-A, which occurs in a DNA replication-independent manner. Here, we examined whether CHD1 participates in the assembly of CenH3CID in Drosophila. In contrast to the findings in fission yeast and vertebrate cells, our evidence clearly argues against such a role for CHD1 in Drosophila. CHD1 does not localize to centromeres in either S2 cells or developing fly embryos. Down-regulation of CHD1 in S2 cells by RNAi reveals unchanged levels of CenH3CID at the centromeres. Most notably, ablation of functional CHD1 in Chd1 mutant fly embryos does not interfere with centromere and kinetochore assembly, as the levels and localization of CenH3CID, CENP-C and BubR1 in the mutant embryos remain similar to those seen in wild-type embryos. These results indicate that Drosophila CHD1 has no direct function in the incorporation of the centromeric H3 variant CenH3CID into chromatin. Therefore, centromeric chromatin assembly may involve different mechanisms in different organisms.
Highlights
The incorporation of variants of the histones H3 and H2A, such as H3.3, CenH3 or H2A.Z, into chromatin correlates with functional specification of genomic regions and is thought to contribute to the epigenetic memory of a cell [1]
We have recently shown that in vivo, CHD1 is required for the replication and transcriptionindependent genome-wide assembly of the variant histone H3.3 in the paternal pronucleus and in transcriptionally active nuclei during embryonic development [5], confirming its role as a chromatin assembly factor
To investigate the role of Drosophila CHD1 in CenH3CID incorporation into chromatin, we examined the potential colocalization of CHD1 with CenH3CID at centromeres in Drosophila S2 cells
Summary
The incorporation of variants of the histones H3 and H2A, such as H3.3, CenH3 or H2A.Z, into chromatin correlates with functional specification of genomic regions and is thought to contribute to the epigenetic memory of a cell [1]. The concerted action of histone chaperones and ATPutilizing factors is required for histone deposition and nucleosome arrangement [2,3]. The ATP-dependent motor protein Drosophila CHD1 mediates the reconstitution of periodic nucleosome arrays in conjunction with the histone chaperone NAP1 in an in vitro chromatin assembly system [4]. We have recently shown that in vivo, CHD1 is required for the replication and transcriptionindependent genome-wide assembly of the variant histone H3.3 in the paternal pronucleus and in transcriptionally active nuclei during embryonic development [5], confirming its role as a chromatin assembly factor
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