Stimulated by retinoic acid gene 8 (STRA8) interacts with the germ cell specific bHLH factor SOHLH1 and represses c-KIT expression in vitro.

STRA8 (Stimulated by Retinoic Acid Gene 8) controls the crucial decision of germ cells to engage meiotic division up and down-regulating genes involved in the meiotic programme. It has been proven as an amplifier of genes involved in cell cycle control and chromosome events, however, how STRA8 functions as negative regulator are not well understood. In this study, we demonstrate that STRA8 can interact with itself and with other basic Helix-Loop-Helix (bHLH) transcription factors through its HLH domain and that this domain is important for its ability to negatively interfere with the Ebox-mediated transcriptional activity of bHLH transcription factors. Significantly, we show that STRA8 interacts with TCF3/E47, a class I bHLH transcription factors, and with SOHLH1, a gonadal-specific bHLH, in male germ cells obtained from prepuberal mouse testis. We demonstrated that STRA8, indirectly, is able to exert a negative control on the SOHLH1-dependent stimulation of c-KIT expression in late differentiating spermatogonia and preleptotene spermatocytes. Although part of this results were obtained only 'in vitro', they support the notion that STRA8 interacting with different transcription factors, besides its established role as 'amplifier' of meiotic programme, is able to finely modulate the balance between spermatogonia proliferation, differentiation and acquisition of meiotic competence.

Expression and possible roles of extracellular signal-related kinases 1-2 (ERK1-2) in mouse primordial germ cell development.

In the present work, we described the expression and activity of extracellular signal-related kinases 1-2 (ERK1-2) in mouse primordial germ cells (PGCs) from 8.5-14.5 days post coitum (dpc) and investigated whether these kinases play a role in regulating the various processes of PGC development. Using immunofluorescence and immunoblotting to detect the active phosphorylated form of ERK1-2 (p-ERK1-2), we found that the kinases were present in most proliferating 8.5-10.5 dpc PGCs, low in 11.5 dpc PGCs, and progressively increasing between 12.5-14.5 dpc both in female and male PGCs. In vitro culture experiments showed that inhibiting activation of ERK1-2 with the MEK-specific inhibitor U0126 significantly reduced the growth of 8.5 dpc PGCs in culture but had little effect on 11.5-12.5 dpc PGCs. Moreover, we found that the inhibitor did not affect the adhesion of 11.5 dpc PGCs, but it significantly reduced their motility features onto a cell monolayer. Further, while the ability of female PGCs to begin meiosis was not significantly affected by U0126, their progression through meiotic prophase I was slowed down. Notably, the activity of ERK1-2 was necessary for maintaining the correct expression of oocyte-specific genes crucial for germ cells survival and the formation of primordial follicles.