Transcriptional control of KIT gene expression during germ cell development.

The characterization of the mechanisms that regulate KIT expression in germ cells at different times of their development is important not only in the field of reproduction, but also for a better understanding of the biology of testicular germ cell tumors (TGCTs). Indeed this tyrosine kinase receptor, besides being essential for the survival and proliferation of primordial germ cells (PGCs) and for postnatal spermatogenesis and oogenesis, is also frequently overexpressed or constitutively active due to activating mutations in carcinoma in situ of the testis and in seminomas. In this review, I will summarize available data about the transcriptional mechanisms involved in the control of Kit expression in the germline. Variable mechanisms, involving different germ cell-specific transcription factors, are operating in the various developmental stages: SOX2 and SOHLH1/2 act as direct positive regulators in PGCs and in postnatal spermatogonia, respectively, whereas PLZF suppresses KIT expression in spermatogonial stem cells. DMRT1, acting through indirect mechanisms, suppresses KIT transcription in fetal gonocytes, while activating it in differentiating spermatogonia.