Immunohistochemical localization of androgen receptor in rat oocytes

Immunohistochemical localization of androgen receptor (AR) was investigated in the rat oocytes during their development in the primary, secondary and antral follicles. The group of experimental Wistar rats included prepubertal female rats, killed at 30 days of age, and mature female rats killed at estrus or metestrus. Excised ovaries were submitted to immunohistochemical procedure in which polyclonal antibody against androgen receptor, avidin-biotin-peroxidase complex, and DAB were used. Characteristic changes in AR immunostaining intensity and localization in the oocyte compartments were observed during the oocyte growth. Relatively strong cytoplasmic AR immunostaining of oocytes from the primordial, primary and some secondary follicles became gradually weaker during the further oocyte development and was only weakly positive in the oocytes from the antral follicles. Germinal vesicles (GVs) usually displayed less intense AR immunostaining than cytoplasm and it was decreasing together with the cytoplasmic depletion of AR. On the contrary, nucleoli appeared as moderately AR-positive structures in the early secondary follicles and were strongly AR-positive in the multilaminar secondary and antral follicles. The presence of AR in the nucleoli persisted even when oocytes had undergone fragmentation in atretic follicles. These findings suggest that during the oocyte growth AR translocates from the oocyte cytoplasm to GV, and then to the nucleolus, which seems to become the main target for this receptor. A possible role of AR in the GV nucleolus is obscure. However, nucleolus contains rRNA genes and is the site of an active transcription, so the role of AR as a ligand-activated, transcriptional factor cannot be excluded.