C-KIT is a cell surface tyrosine kinase receptor whose ligand, SCF (also known as Kit ligand (KL)), causes dimerisation of C-KIT and downstream phosphorylation of intracellular pathways (Saiti and Lacham-Kaplan, 2007). Its role in murine germ cell development is long established, with expression detected from the time of PGC specification to the point of meiotic entry, then disappearing until oocytes enter the diplotene stage (Manova and Bachvarova, 1991). Mutations in the c-kit gene do not affect PGC specification, but does have a detrimental effect on PGC proliferation, indicating its mitogenic role (Besmer et al., 1993). In the post-natal ovary, oocytes express c-kit, whilst surrounding granulosa cells express SCF; mutations affecting SCF expression lead to follicular arrest at the primary stage, suggesting that these molecules are involved in oocyte growth (Besmer et al., 1993).

Human C-KIT expression has been demonstrated in oogonia and post-natal oocytes at all stages of development (Horie et al., 1993, Robinson et al., 2001, Stoop et al., 2005). The interspecies variation in expression seen in POU5F1 between mouse and human is again observed, with human C-KIT expression persisting throughout fetal development (Stoop et al., 2005). This difference in both POU5F1 and C-KIT expression may be explained by the asynchronous entry of human PGCs into meiosis: this may result in mitotic PGCs continuing to express C-KIT whilst those undergoing meiosis cease to produce it, thereby there is no hiatus in apparent expression as seen in the mouse. In contrast to POU5F1 expression, however, C-KIT expression is maintained in oocytes after POU5F1 expression has declined (Stoop et al., 2005). C-KIT also has roles in melanogenesis and haematopoiesis (Besmer et al., 1993), therefore, as with PRDM1, cannot be regarded as a germ cell-specific marker.