The mammalian germline as a pluripotency cycle.

Naive pluripotency refers to the capacity of single cells in regulative embryos to engender all somatic and germline cell types. Only germ cells - conventionally considered to be unipotent - can naturally re-acquire pluripotency, by cycling through fertilisation. Furthermore, primordial germ cells express, and appear to be functionally dependent upon, transcription factors that characterise the pluripotent state. We hypothesise that germ cells require pluripotency factors to control a de-restricted epigenome. Consequently, they harbour latent potential, as manifested in teratocarcinogenesis or direct conversion into pluripotent stem cells in vitro. Thus, we suggest that there exists an unbroken cycle of pluripotency, naive in the early epiblast and latent in the germline, that is sustained by a shared transcription factor network.