Germline development in amniotes: A paradigm shift in primordial germ cell specification. (6th June 2016) - Bertocchini, Federica
Abstract : In the field of germline development in amniote vertebrates, primordial germ cell (PGC) specification in birds and reptiles remains controversial. Avians are believed to adopt a predetermination or maternal specification mode of PGC formation, contrary to an inductive mode employed by mammals and, supposedly, reptiles. Here, we revisit and review some key aspects of PGC development that channelled the current subdivision, and challenge the position of birds and reptiles as well as the 'binary' evolutionary model of PGC development in vertebrates. We propose an alternative view on PGC specification where germ plasm plays a role in laying the foundation for the formation of PGC precursors (pPGC), but not necessarily of PGCs. Moreover, inductive mechanisms may be necessary for the transition from pPGCs to PGCs. Within this framework, the implementation of data from birds and reptiles could provide new insights on the evolution of PGC specification in amniotes. Abstract : PGC specification is currently believed to occur according to two modalities, maternal specification or induction. We propose an alternative view whereby maternal determinants (germ plasm), when present, guide specification of (multipotent) PGC precursors (pPGCs), but induction is needed for the transition from pPGCs to PGCs in amniotes, and perhaps all animals (The existence of germ line stem cells is sex and/or species dependent).