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XB-ART-49123
Development June 1, 2014; 141 (12): 2429-40.

Stochastic specification of primordial germ cells from mesoderm precursors in axolotl embryos.

Chatfield J , O'Reilly MA , Bachvarova RF , Ferjentsik Z , Redwood C , Walmsley M , Patient R , Loose M , Johnson AD .


Abstract
A common feature of development in most vertebrate models is the early segregation of the germ line from the soma. For example, in Xenopus and zebrafish embryos primordial germ cells (PGCs) are specified by germ plasm that is inherited from the egg; in mice, Blimp1 expression in the epiblast mediates the commitment of cells to the germ line. How these disparate mechanisms of PGC specification evolved is unknown. Here, in order to identify the ancestral mechanism of PGC specification in vertebrates, we studied PGC specification in embryos from the axolotl (Mexican salamander), a model for the tetrapod ancestor. In the axolotl, PGCs develop within mesoderm, and classic studies have reported their induction from primitive ectoderm (animal cap). We used an axolotl animal cap system to demonstrate that signalling through FGF and BMP4 induces PGCs. The role of FGF was then confirmed in vivo. We also showed PGC induction by Brachyury, in the presence of BMP4. These conditions induced pluripotent mesodermal precursors that give rise to a variety of somatic cell types, in addition to PGCs. Irreversible restriction of the germ line did not occur until the mid-tailbud stage, days after the somatic germ layers are established. Before this, germline potential was maintained by MAP kinase signalling. We propose that this stochastic mechanism of PGC specification, from mesodermal precursors, is conserved in vertebrates.

PubMed ID: 24917499
PMC ID: PMC4050694
Article link: Development
Grant support: [+]

Species referenced: Xenopus
Genes referenced: bmp4 dazl ddx4 inhba mapk1 ncam1 odc1 pgc pik3ca piwil1 prdm1 smad2 tbxt wt1


Article Images: [+] show captions
References [+] :
Ahlberg, The axial skeleton of the Devonian tetrapod Ichthyostega. 2005, Pubmed