Abstract
Embryos of many animal models express germ line determinants that suppress transcription and mediate early germ line commitment, which occurs before the somatic cell lineages are established. However, not all animals segregate their germ line in this manner. The ‘last cell standing’ model describes primordial germ cell (PGC) development in axolotls, in which PGCs are maintained by an extracellular signalling niche, and germ line commitment occurs after gastrulation. Here, we propose that this ‘stochastic’ mode of PGC specification is conserved in vertebrates, including non-rodent mammals. We postulate that early germ line segregation liberates genetic regulatory networks for somatic development to evolve, and that it therefore emerged repeatedly in the animal kingdom in response to natural selection.
Highlights
Germ cells and somatic cells engender perhaps the most basic division of cellular function in metazoan biology
We showed that BMP4 and phospho-SMAD1/5/8 are detected in the posterior end of the embryonic disc (Valdez-Magaña et al, 2014), the area where the primordial germ cell (PGC) are first identified (Wolf et al, 2011; R.A., unpublished observations)
PGC development remains only a probability until relatively late in development: if the niche changes prior to lineage restriction, potential germ cells will be diverted to an alternative fate. We define this as ‘late’ PGC specification and to describe this process we proposed the ‘last cell standing’ model, which postulates that PGCs develop from the last cells in the embryo to engage in lineage commitment (Chatfield et al, 2014)
Summary
Germ cells and somatic cells (or soma) engender perhaps the most basic division of cellular function in metazoan biology. In mouse embryos germ line restriction is induced in transcriptionally active cells by expression of the transcription factor Blimp1 (Prdm1 – Mouse Genome Informatics), which inhibits mesoderm specification in nascent PGCs through repression of a specific set of genes (Ohinata et al, 2005).
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