A 90-kDa glycoprotein exhibited stage-specific expression in meiotic germ cells in rat testes.

We produced a monoclonal antibody, designated MC301, against the extract of testicular cells from 12-day-old rats. This age corresponds to the onset of meiosis during testis development. MC301 specifically recognized a 90-kDa glycoprotein, GP90-MC301, which was ubiquitously expressed in various tissues and localized predominantly in the Golgi area of epithelial cells. In adult testes, stage-specific intense expression of GP90-MC301 was shown in the cytoplasm of meiotic spermatogenic cells from the preleptotene to mid-pachytene stages. Immunoelectron microscopy demonstrated that the glycoprotein was localized in spermatocytes on protein synthesis-related organelles such as the Golgi apparatus, endoplasmic reticulum, and nuclear envelope. The plasma membrane of spermatocytes and the intercellular space surrounding the cells were also immunoreactive. No specific immunoreactivity was found on the organelles in other testicular cells. A considerable amount of the glycoprotein was detected in the extracellular fluid of the testes. These results suggest that GP90-MC301 is produced mainly by spermatocytes in the testis and secreted into the surrounding intercellular space. The evidence for developmentally regulated expression of GP90-MC301 in the meiotic spermatogenic cells suggests a possible role for the glycoprotein in male germ cell meiosis.