Spt6 is a maintenance factor for centromeric CENP-A

Abstract

Replication and transcription of genomic DNA requires partial disassembly of nucleosomes to allow progression of polymerases. This constitutes both an opportunity 2 to remodel the underlying chromatin as well as the potential danger of losing epigenetic information. Centromeric transcription has been shown to be required for stable incorporation of the centromere-specific histone dCENP-A in M/G1-phase, which depends on the eviction of previously deposited H3/H3.3-placeholder nucleosomes.Here we demonstrate that the histone chaperone and transcription elongation factor Spt6 spatially and temporarily coincides with centromeric transcription and prevents the loss of old CENP-A nucleosomes in both Drosophila and human cells. Spt6 binds directly to dCENP-A and shows enhanced association with non-phosphorylatable dCENP-A mutants compared to histone H3, while phosphomimetic residues alleviate association with Spt6. We conclude that Spt6 acts as a conserved CENP-A maintenance factor, which is required during transcription-mediated chromatin remodelling at the centromere to ensure long-term stability of epigenetic centromere identity.

Centromeric Transcription: A Conserved Swiss-Army Knife

“…Direct evidence came from work in mammalian cell lines and Xenopus oocyte extracts where knock-down of centromeric transcripts resulted in reduced CENP-A levels at the centromere [ 21 , 24 , 25 , 26 , 33 , 48 ]. Indeed, recent work in mammalian and fruit fly cell lines showed that chemical inhibition of activated RNAP2 resulted in the loss of centromeric CENP-A CID chromatin [ 21 , 52 ]; and the elongation factor Spt6 facilitates maintenance of centromeric CENP-A CID [ 105 ]. These lines of investigation strongly hint at a distinct role for both the act of transcription and the production of an RNA species in the loading of CENP-A.…”

“…It is not very likely that new CENP-A is loaded exclusively on naked DNA, rather than on chromatin. Indeed, in human and fruit fly cell lines, active transcription is needed to remove so-called placeholder H3.3 nucleosomes prior to new CENP-A loading at the centromere [ 53 , 105 , 106 ]. Similarly, in fission yeast, H3 nucleosomes function as placeholder nucleosomes [ 61 ].…”

Polo kinase recruitment via the constitutive centromere-associated network at the kinetochore elevates centromeric RNA

“…Interestingly, the Spt6-RNAPII association is required for efficient recruitment of the Ccr4-Not mRNA-processing and deadenylation complex [ 132 ]. It was recently shown, in both Drosophila and human cells, that Spt6 is directly involved in CEN transcription and CENP-A maintenance [ 133 ]. Spt5 contributes to the recruitment of the mRNA capping enzyme [ 134 ].…”

Genetic screening identifies a SUMO protease dynamically maintaining centromeric chromatin and the associated centromere complex

“…General components of the transcription machinery such as the POLR2B, a subunit of RNA polymerase II and CDK9 P-TEFb , a critical kinase in the transcription elongation complex (Cho et al, 2010) also impact on CENP-A maintenance as well as assembly (for POLR2B). Pleiotropic effects of depleting these general transcription-related proteins cannot be excluded but nevertheless these factors are of interest as a direct role for transcription in CENP-A maintenance and assembly has been suggested (Bobkov et al, 2019(Bobkov et al, , 2018Bergmann et al, 2011).…”