Expression and localization of 25-Dx, a membrane-associated putative progesterone-binding protein, in the developing Purkinje cell.

Neurosteroids are synthesized de novo in the brain and the cerebellar Purkinje cell is a major site for neurosteroid formation. We have demonstrated that the rat Purkinje cell actively produces progesterone de novo from cholesterol only during neonatal life and progesterone promotes dendritic growth, spinogenesis and synaptogenesis via its nuclear receptor in this neuron. On the other hand, 25-Dx, a putative membrane progesterone receptor, has been identified in the rat liver. In this study, we therefore investigated the expression and localization of 25-Dx in the Purkinje cell to understand the mode of progesterone actions in this neuron. Reverse transcription-PCR and Western immunoblot analyses revealed the expressions of 25-Dx mRNA and 25-Dx-like protein in the rat cerebellum, which increased during neonatal life. By immunocytochemistry, the expression of 25-Dx-like protein was localized in the Purkinje cell and external granule cell layer. At the ultrastructural level, we further found that 25-Dx-like immunoreactivity was associated with membrane structures of the endoplasmic reticulum and Golgi apparatus in the Purkinje cell. These results indicate that the Purkinje cell expresses the putative membrane progesterone receptor, 25-Dx during neonatal life. Progesterone may promote dendritic growth, spinogenesis and synaptogenesis via 25-Dx as well as its nuclear receptor in the Purkinje cell in the neonate.