Figure 1.

Three possible sources of ALCs in fetal and neonatal mouse testes: peritubular progenitors (Hes1+/Arx+) that come from coelomic epithelium (21); perivascular progenitors (nestin+/Notch+) that come from the gonadal-mesonephros border (22); and dedifferentiated FLCs that occur by the end of the fetal stage (23). Depending on the source, SLCS may differ in their dependence on Dhh and Notch signaling. Thus, the differentiation of the peritubular progenitors depends more on the activation of Dhh signaling (21), while the differentiation of perivascular lineage depends more on the deactivation of Notch signaling (22).