These areas of FGF4 expression in the preimplantation and postimplantation embryo closely match expected locations for PGCs. Other FGFs, especially FGF-3 and FGF-5, have also been shown to be expressed in tissues immediately adjacent to those expressing FGF-4. These observations suggest that FGFs may be continuously available to premigratory and migratory PGCs. Mice lacking either a functional FGF-3 or FGF-5 gene are fertile, indicating that some PGCs mature in the absence of either factor. Embryos deficient in FGF-4 cease development prior to PGC proliferation, as do embryos lacking functional FGFR-1, preventing an analysis of PGC development in these embryos. Mice lacking a functional FGFR-2 are not presently available. antibiotic levaquin
FGF may play important roles during gametogenesis, as bFGF has been detected both in murine ovarian follicles and in rat spermatocytes. Another member of this growth factor family, FGF-8, may also be present in prespermato-gonia between 15 and 17 dpc.
The reduction in FGF binding by 13.5 dpc oogonia as they enter meiosis was an unexpected finding.