Expression of the p63 and Notch signaling systems in rat testes during postnatal development: comparison with their expression levels in the epididymis and vas deferens

The role of tubular structures that contribute to the passage of spermatozoa is not solely passive; these structures actively contribute to their own functions, although these tubules and ducts are contiguous and collaborate in the development of the male gamete along their lengths. The testis has the specific function to generate spermatozoa and spermatozoa undergo numerous changes as they pass through the epididymis. A member of the p53 family of genes, p63, is highly expressed in the basal layers of epithelial tissues and plays a key role in maintaining their cell populations, whereas Notch 1 and its ligand Jagged 2 have an important role in the differentiation of germ cells and Jagged 2 is up-regulated by TAp63, one of the p63 isoforms, which transactivates p53 target genes and induces apoptosis. Although the presence of p63 in most epithelia is established, the role of p63 and its possible relationship with the Notch system in the seminiferous epithelium have not been examined. Therefore, we investigated the expression of p63, Jagged 2, and Notch 1 in the testis during postnatal development in comparison with their expression levels in the vaso-epididymal epithelium. In the testis, the expression of TAp63 mRNA increased at day 14 after birth and the expressions of Jagged 2 and Notch 1 mRNA increased at day 16 after birth, suggesting that TAp63-mediated Jagged 2 induction activates the Notch signaling system. On the other hand, the strong signal of DeltaNp63 mRNA was already recognized in the vas deferens at day 0 after birth and advanced chronologically along the duct to the caput epididymis and p63 protein was expressed in basal cells in their epithelium, whereas the mRNAs of Jagged 2 and Notch 1 were maintained at a low level. Consequently, examination of our data raises the probability that TAp63 has an important role for maintenance of germ cell numbers, triggering or balancing the development, differentiation, and apoptosis of germ cells in the testis, which is completely different from the role of DeltaNp63 in other epithelial tissues.