Ligand-dependent regulation of retinoic acid receptor alpha in rat testis: in vivo response to depletion and repletion of vitamin A.

Male animals are sterile due to testicular degeneration in the absence of retinoic acid (RA) or functional retinoic acid receptor-alpha (RAR alpha). This degeneration can be reversed by injecting retinol, a precursor of RA, into vitamin A-deficient (VAD) rats. To determine the relationship between this ligand-dependent testicular degeneration and regeneration and the expression levels of RAR alpha messenger RNA and protein, testes were depleted and then replenished with retinol in vivo. Results showed that RAR alpha messenger RNA and protein levels declined to VAD amounts after 7 weeks on a VAD diet. This decline was due to decreased RAR alpha levels in early meiotic spermatocytes and the loss of advanced germ cells. Interestingly, the advanced germ cells still contained RAR alpha, but the protein was primarily cytoplasmic instead of nuclear, indicating inactivity as a transcription factor. In VAD testis, RAR alpha levels were low and then increased primarily in Sertoli cells after retinol replenishment. TUNEL analyses showed that most germ cells at the basal aspect of seminiferous tubules were undergoing apoptosis during degeneration. These results indicate that RAR alpha is either down-regulated or inactivated in RA-deficient testis and coincident with that, testes degenerate by apoptosis or selective loss of germ cells.