Cloning and localization of Rab3 isoforms in bovine, rat, and human parathyroid glands

Rab3 proteins are small GTP-binding proteins known to play a role in regula ted exocytosis processes. This study examines the expression of Rab3 mRNA a nd protein in bovine, rat and human parathyroid glands. mRNAs of several Ra b3 isoforms were detected in bovine (Rab3A, Rab3B and Rab3C) and rat (Rab3A , Rab3B and Rab3D) parathyroid glands by RT-PCR and sequencing. Rab3A prote in was detected in the cytosolic extract from bovine parathyroid gland by W estern blotting using a monoclonal antibody for Rab3A. Rab3A protein was lo calized to parathyroid hormone-containing chief cells by immunohistochemica l staining. Subcellular localization of Rab3A protein by immunogold electro n microscopy revealed that the majority of Rab3A protein was not associated with dense-core vesicles, but localized in the cytosol of the chief cells. Altogether, our results demonstrate that Rab3 isoforms are expressed in pa rathyroid chief cells, suggesting that they may play a role in regulated ex ocytosis in these cells. (C) 1999 Academic Press.