Reproduction Abstracts

Introduction: Neuronatin (NNAT) is first identified in the neonatal neural tissue and is assumed to be involved in embryonic neurogenesis. Although defect of PROP1, a pituitary specific transcription factor important for pituitary organogenesis, causes reduced expression of the Nnat, the cellular localization and the vital roles of NNAT in the pituitary are still unclear. The present study examined the population of the NNAT-positive cells as to understand the role of NNAT in the pituitary.

Materials and methods: Ontogeny of NNAT expression by real-time PCR and immunohistochemistry for embryonic and postnatal pituitaries were performed.

Results and discussion: Real-time PCR showed that Nnat is abundantly expressed in the prenatal period and markedly decreased after birth. Immunohistochemistry showed that NNAT-signals were detected in the SOX2-positive cells in the pituitary primordium at embryonic day (E) 11.5, followed by appearance in all of pituitary cells at E13.5. On E21.5, the number of NNAT-positive cells gradually decreased. At E13.5, they were positive for PROP1 and then both proteins independently faded from the developing pituitary cells. Staining with cocktail of antibodies for pituitary hormones showed a small number of NNAT/hormone-double positive cells on E21.5. In the adult pituitary, a small number SOX2-positive cells were present and a few of them were positive for NNAT. Notably, there were other NNAT-positive cells negative to PROP1 and hormones as well as SOX2 suggesting that NNAT plays a role in SOX2-positive stem/progenitor cells, which launch to differentiate, and disappears in the terminal stage.