HIRA dependent H3.3 deposition is required for transcriptional reprogramming following nuclear transfer to Xenopus oocytes

Abstract

BackgroundNuclear reprogramming is potentially important as a route to cell replacement and drug discovery, but little is known about its mechanism. Nuclear transfer to eggs and oocytes attempts to identify the mechanism of this direct route towards reprogramming by natural components. Here we analyze how the reprogramming of nuclei transplanted to Xenopus oocytes exploits the incorporation of the histone variant H3.3.ResultsAfter nuclear transplantation, oocyte-derived H3.3 but not H3.2, is deposited on several regions of the genome including rDNA, major satellite repeats, and the regulatory regions of Oct4. This major H3.3 deposition occurs in absence of DNA replication, and is HIRA-and transcription-dependent. It is necessary for the shift from a somatic- to an oocyte-type of transcription after nuclear transfer.ConclusionsThis study demonstrates that the incorporation of histone H3.3 is an early and necessary step in the direct reprogramming of somatic cell nuclei by oocyte. It suggests that the incorporation of histone H3.3 is necessary during global changes in transcription that accompany changes in cell fate.

Single Cell Analysis of RNA-mediated Histone H3.3 Recruitment to a Cytomegalovirus Promoter-regulated Transcription Site

“…Disruption of RI H3.3 chromatin assembly negatively impacts nuclear reprogramming (53,54), gametogenesis (55)(56)(57), and fertilization (30,58), indicating a critical mode of action in epigenetic regulation. Here, we provide evidence that H3.3 is recruited to a RI incorporation site (an array of a CMV promoter-regulated transgene) through an RNA-mediated chaperone-independent mechanism.…”

Histone variants in pluripotency and disease

“…A recent report investigating the reprogramming of mammalian nuclei transplanted to Xenopus oocytes showed that the Hiradependent deposition of H3.3 at Oct4 was required for transcriptional reprogramming (Jullien et al, 2012). Impaired reprogramming in the absence of Hira and H3.3 deposition could not be compensated for by the increased deposition of the histone variant H3.2, again suggesting that H3.3 performs a more important function than simple gap-filling following nucleosome remodeling.…”

Histone Variant H3.3: A versatile H3 variant in health and in disease

“…On the other hand, H3.3 is required for the reactivation of key pluripotency genes of the donor nucleus. It has been shown that exogenous H3.3 deposits at not only the regulatory regions of Oct4, but also other genomic regions, including the major satellite repeats and rDNA (Jullien et al, 2012). In addition, knockdown of maternal H3.3 results in compromised reprogramming and failure to reactivate key pluripotency genes, such as Oct4 in mouse embryos (Wen et al, 2014a).…”