Dose-dependent functions of fibroblast growth factor 9 regulate the fate of murine XY primordial germ cells†

Abstract

Male differentiation of primordial germ cells (PGCs) is initiated by the inhibition of entry into meiosis and exposure to male-inducing factor(s), which are regulated by somatic elements of the developing gonad. Fibroblast growth factor 9 (FGF9) produced by pre-Sertoli cells is essential for male gonadal differentiation and also contributes to survival and male differentiation of XY PGCs. However, it is not clear how FGF9 regulates PGC fate. Using a PGC culture system, we identified dose-dependent, fate-determining functions of FGF9 in XY PGCs. Treatment with low levels of FGF9 (0.2 ng/ml) increased expression of male-specific Dnmt3L and Nanos2 in XY PGCs. Conversely, treatment with high levels of FGF9 (25 ng/ml) suppressed male-specific gene expression and stimulated proliferation of XY PGCs. Western blotting showed that low FGF9 treatment enhanced p38 MAPK (mitogen-activated protein kinase) phosphorylation in the same cells. In contrast, high FGF9 treatment significantly stimulated the ERK (extracellular signal-regulated kinase)1/2 signaling pathway in XY PGCs. We investigated the relationship between the ERK1/2 signaling pathway stimulated by high FGF9 and regulation of PGC proliferation. An ERK1/2 inhibitor (U0126) suppressed the PGC proliferation that would otherwise be stimulated by high FGF9 treatment, and increased Nanos2 expression in XY PGCs. Conversely, a p38 MAPK inhibitor (SB202190) significantly suppressed Nanos2 expression that would otherwise be stimulated by low FGF9 in XY PGCs. Taken together, our results suggest that stage-specific expression of FGF9 in XY gonads regulates the balance between proliferation and differentiation of XY PGCs in a dose-dependent manner. Summary SentenceFGF9 directly regulates different fates of XY PGCs in a dose-dependent manner: low FGF9 treatment promotes p38 signaling pathway to induce PGC male differentiation, whereas high FGF9 treatment enhances ERK1/2 signaling pathway to proliferate PGCs. 122

Retinoic Acid Antagonizes Testis Development in Mice

“…We speculated that any such role might be in addition to and independent of the direct effects of RA on germ cell development. Such a scenario would be similar to what we know of FGF9 signaling: FGF9 reinforces the Sertoli cell differentiation pathway in males (Jameson et al, 2012a;Kim et al, 2006) but also independently promotes male germ cell development (Bowles et al, 2010;Ulu et al, 2017). The hypothesis that RA is required to feminize somatic cells during ovary development was recently addressed: the conclusion reached was that RA signaling is not required for granulosa cell specification, differentiation, or reproductive function (Minkina et al, 2017).…”

A threshold model for receptor tyrosine kinase signaling specificity and cell fate determination

“…Manipulation of PDGFR expression levels also showed a quantitative relationship between receptor expression levels and the vascular smooth muscle phenotype. Additional support for Marshall’s model has been provided by cell-based studies showing that changing the concentration (and thus the signaling strength) of FGF2 or FGF8, and FGF9, respectively, induces distinct responses in pre-somitic mesoderm and primordial germ cells 44 , 45 .…”

Regulation of fibroblast growth factor 8 (FGF8) in chicken embryonic stem cells differentiation into spermatogonial stem cells

“…G, Immunofluorescence assay and FCMs evaluation of SSCs production in different groups (600×) phosphorylation to inhibit MAPK/ERK signaling pathway, while up-regulation of FGFs were the opposite result. 10,12,23,24 In the process of MAPK/ERK signaling (Figure 6A), FGFR2 is a tyrosine kinase receptor that binds to FGF8, which cause tyrosine kinases to form homodimers and leads to the expression and activation of downstream genes. GRB2 is the member of the growth factor binding protein family, involved in FGFR-mediated signal transduction, RAF is the member of the MAPKK kinase family.…”

“…Moreover, knockout of FGF7 can induced increased SSCs death rate. Ulu et al 10 demonstrated that FGF9 directly acts on and regulates PGCs in a dosedependent manner. It promotes differentiation into SSCs in low expression (0.2 ng/mL) while facilitates PGCs selfrenewal and inhibits differentiation when highly expressed (25 ng/mL).…”