Specification of the germ cell lineage in mice: a process orchestrated by the PR-domain proteins, Blimp1 and Prdm14.

Germ cell specification in mice, which generates primordial germ cells (PGCs), the common source of the oocytes and spermatozoa, from the epiblast, integrates three key events: repression of the somatic program, re-acquisition of potential pluripotency, and genome-wide epigenetic reprogramming. A PR-domain containing protein, Blimp1 (also known as Prdm1), has been identified as a critical factor for PGC specification. Using a highly representative single-cell microarray technology, we identified a complex but highly ordered genome-wide transcription dynamics associated with PGC specification. This analysis not only demonstrated a dominant role of Blimp1 for the repression of the genes normally downregulated in PGCs relative to their somatic neighbors, but also revealed the presence of gene expression programs initiating independently from Blimp1. Among such programs, we identified Prdm14, another PR-domain containing protein, as a key regulator for the re-acquisition of potential pluripotency and genome-wide epigenetic reprogramming. The launch of the germ cell lineage in mice, therefore, is orchestrated by two independently acquired, PR domain-containing transcriptional regulators, Blimp1 and Prdm14.