Combinatorial control of cell fate and reprogramming in the mammalian germline.

Development of mammalian primordial germ cells (PGCs) presents a unique example of a cell fate specification event that is intimately linked with epigenetic reprogramming. Cell fate commitment is governed by transcription factors which, together with epigenetic regulators, instruct lineage choice in response to signalling cues. Similarly, the reversal of epigenetic silencing is driven by the combinatorial action of transcriptional regulators, resulting in an increase in cellular plasticity. PGCs constitute a paradox, since their development as a unipotent specialised lineage is coupled with extensive reprogramming, which eventually leads to an increase in cellular potency. In this review we discuss the role of key factors in the specification of the germ cell lineage that are also important for the comprehensive erasure of epigenetic modifications, which provides the foundation for regeneration of totipotency. We further discuss current concepts of transcriptional and epigenetic control of cell fate decisions, with a particular focus on emerging principles of enhancer activity and their potential implications for the transcriptional control of PGC specification.