title: Proximal visceral endoderm and extraembryonic ectoderm regulate the formation of primordial germ cell precursors.
abstract: BACKGROUND
  The extraembryonic tissues, visceral endoderm (VE) and extraembryonic ectoderm (ExE) are known to be important for the induction of primordial germ cells (PGCs) in mice via activation of the bone morphogenetic protein (BMP) signalling pathway. We investigated whether the VE and ExE have a direct role in the specification of PGCs, or in an earlier event, namely the induction of the PGC precursors in the proximal posterior epiblast cells.
  
  
  RESULTS
  We cultured embryonic day (E) 5.75 to E7.0 mouse embryos in an explant-assay with or without extraembryonic tissues. The reconstituted pieces of embryonic and extraembryonic tissues were assessed for the formation of both PGC precursors and specified PGCs. For this, Blimp1:gfp and Stella:gfp transgenic mouse lines were used to distinguish between PGC precursors and specified PGC, respectively. We observed that the VE regulates formation of an appropriate number of PGC precursors between E6.25-E7.25, but it is not essential for the subsequent specification of PGCs from the precursor cells. Furthermore, we show that the ExE has a different role from that of the VE, which is to restrict localization of PGC precursors to the posterior part of the embryo.
  
  
  CONCLUSIONS
  We show that the VE and ExE have distinct roles in the induction of PGC precursors, namely the formation of a normal number of PGC precursors, and their appropriate localization during early development. However, these tissues do not have a direct role during the final stages of specification of the founder population of PGCs.
authors: The Wellcome Trust/Cancer Research UK Gurdon Institute, University of Cambridge, Tennis Court Road, Cambridge CB2 1QN, UK. smc80@cam.ac.uk
authors: Susana M Chuva
authors: SM
authors: de Sousa Lopes
authors: Katsuhiko
authors: K
authors: Hayashi
authors: M Azim
authors: MA
authors: Surani
mesh_terms: D000818:Animals; D004475:Ectoderm / Q000166:cytology*; D046149:Embryo Culture Techniques; D004622:Embryo, Mammalian; D004627:Embryonic Induction; D053595:Embryonic Stem Cells / Q000166:cytology*; D004707:Endoderm / Q000166:cytology*; D005854:Germ Cells / Q000166:cytology*; D051379:Mice; D008822:Mice, Transgenic