Regulation by pH of the alternative splicing of the stem cell factor pre-mRNA in the testis

Proliferation and differentiation of progenitor stem cells are mainly contr olled by diffusible and adhesion molecules. Stem cell factor (SCF), an esse ntial regulator of spermatogenesis produced by Sertoli cells, utilize both modes of cell to cell communication. Indeed, SGF exists in soluble (SCFs) a nd membrane-bound (SCFm) forms, which are required for a complete spermatog enesis, and are generated by alternative splicing of optional exon 6, encod ing sites of proteolysis. We show that in the mouse testis, the alternative splicing of SCF is developmentally regulated. SCFs predominates in fetal a nd neonatal gonads and is then replaced by SCFm in the prepubertal and adul t gonads. By sequencing SCF exon 6, we show that the flanking intronic sequ ences perfectly follow the gt-at rule, suggesting that the basal splicing m achinery might not be responsible by itself for exon 6 skipping. Moreover, freshly isolated Sertoli cells mainly express SCFm, but a switch to SCFs oc curs after 48 h of culture. We found that this change can be prevented by a cidification of the culture medium at pH 6.3 or by addition of lactate. The sustained synthesis of SCFm at low pH was no longer observed in the presen ce of cycloheximide, suggesting that SCF exon 6 skipping requires de novo p rotein synthesis. Accordingly, UV cross-linking experiments show that nucle ar Sertoli cell protein(s) bind in a sequence-specific manner to exon 6. To gether, our data allow the proposal of an integrated mechanism in which the synthesis of lactate by Sertoli cells is used in the same time as an energ etic substrate for germ cells and as a promoter of their survival/prolifera tion through the production of SCFm.