Initiation and maintenance of pluripotency gene expression in the absence of cohesin

Abstract

Cohesin is implicated in establishing and maintaining pluripotency. Whether this is because of essential cohesin functions in the cell cycle or in gene regulation is unknown. Here we tested cohesin's contribution to reprogramming in systems that reactivate the expression of pluripotency genes in the absence of proliferation (embryonic stem [ES] cell heterokaryons) or DNA replication (nuclear transfer). Contrary to expectations, cohesin depletion enhanced the ability of ES cells to initiate somatic cell reprogramming in heterokaryons. This was explained by increased c-Myc (Myc) expression in cohesin-depleted ES cells, which promoted DNA replicationdependent reprogramming of somatic fusion partners. In contrast, cohesin-depleted somatic cells were poorly reprogrammed in heterokaryons, due in part to defective DNA replication. Pluripotency gene induction was rescued by Myc, which restored DNA replication, and by nuclear transfer, where reprogramming does not require DNA replication. These results redefine cohesin's role in pluripotency and reveal a novel function for Myc in promoting the replication-dependent reprogramming of somatic nuclei.

Cohesin's role in pluripotency and reprogramming

“…12,28,48 Alternatively, cohesin can be acutely depleted from cycling cells at the gene level (by inducible deletion) or the protein level (by inducible cleavage or degradation), provided that depletion is sufficiently rapid to occur within a single cell cycle. Our experiments combined inducible ERt2Cre and conditional Rad21 alleles 41 to efficiently deplete mRNA ( Fig. 2A) and protein ( Fig.…”

“…1,[38][39][40] However, gene expression analysis in ES cells 5 d after cohesin knockdown 1 revealed a preferential deregulation of genes related to cell cycle and DNA damage. 41 Prolonged depletion of cohesin from rapidly dividing ES or iPS cells can therefore result in DNA damage, checkpoint activation, cell cycle arrest and the induction of p53 target gene expression (Fig. 1B).…”

“…These experiments indicated that cohesin was not specifically required for reprogramming, and that ES cells maintained the expression of most pluripotency genes when analyzed after cohesin depletion but before the onset of DNA damage responses. 41 Here we take this analysis to its logical conclusion by showing that deliberately inflicted DNA damage -or the DNA damage resulting from prolonged cohesin depletion in cycling ES cells -actively interferes with pluripotency and reprogramming. Our findings suggest that data concerning the role of cohesin in pluripotency and reprogramming derived from cells that cycle in the absence of cohesin should be reinterpreted in the context of essential cohesin functions in the cell cycle.…”

An Overview of Genome Organization and How We Got There: from FISH to Hi-C

“…Cohesin was shown to colocalize with Mediator genome-wide and facilitated enhancerpromoter looping at the Nanog gene (304). Although it was originally thought to be important for mouse stem cell maintenance by directly regulating the Oct4 and Nanog pluripotent genes (304), a more recent study indicates that this is not likely the case (309).…”

Cycling through developmental decisions: how cell cycle dynamics control pluripotency, differentiation and reprogramming

“…If the erasure of DNA methylation or other epigenetic signatures requires active cell division, this could explain some of the discrepancies described above. It is also possible that DNA replication rather than cell division is mechanistically important for reprogramming (Lavagnolli et al, 2015). Also, the dependency of a lineagespecifying transcription factor on CDK for activation could explain differences in various stem/progenitor cells.…”