Abstract
SummaryNuclear transfer to oocytes is an efficient way to transcriptionally reprogram somatic nuclei, but its mechanisms remain unclear. Here, we identify a sequence of molecular events that leads to rapid transcriptional reprogramming of somatic nuclei after transplantation to Xenopus oocytes. RNA-seq analyses reveal that reprogramming by oocytes results in a selective switch in transcription toward an oocyte rather than pluripotent type, without requiring new protein synthesis. Time-course analyses at the single-nucleus level show that transcriptional reprogramming is induced in most transplanted nuclei in a highly hierarchical manner. We demonstrate that an extensive exchange of somatic- for oocyte-specific factors mediates reprogramming and leads to robust oocyte RNA polymerase II binding and phosphorylation on transplanted chromatin. Moreover, genome-wide binding of oocyte-specific linker histone B4 supports its role in transcriptional reprogramming. Thus, our study reveals the rapid, abundant, and stepwise loading of oocyte-specific factors onto somatic chromatin as important determinants for successful reprogramming.
Highlights
Nuclear reprogramming is of much current interest, especially in view of the potential therapeutic value of cells reprogrammed directly from patients (Tachibana et al, 2013; Wu and Hochedlinger, 2011)
We identify a sequence of molecular events that leads to rapid transcriptional reprogramming of somatic nuclei after transplantation to Xenopus oocytes
RNA-seq analyses reveal that reprogramming by oocytes results in a selective switch in transcription toward an oocyte rather than pluripotent type, without requiring new protein synthesis
Summary
Nuclear reprogramming is of much current interest, especially in view of the potential therapeutic value of cells reprogrammed directly from patients (Tachibana et al, 2013; Wu and Hochedlinger, 2011). While much interest resides in reprogramming to induced pluripotent stem cells (iPSCs), other routes toward reprogramming, such as nuclear transfer (NT) and cell fusion, provide unique experimental advantages to dissect the steps and mechanisms of transcriptional reprogramming, even without the need for cell division in some experimental settings. The transfer of nuclei to second meiotic metaphase oocytes can result in reprogrammed pluripotent cells of high quality and with high efficiency (Kim et al, 2010; Le et al, 2014; Tachibana et al, 2013). It was previously demonstrated that the oocyte system is a useful tool to reveal important factors for the establishment or maintenance of cell identity, which are directly applicable to several other reprogramming systems, such as mouse and human iPSC and mouse NT (Wen et al, 2014; Barrero et al, 2013; Gaspar-Maia et al, 2013; Miyamoto et al, 2013; Pasque et al, 2011, 2012)
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