Retinol differentially regulates male germ cell-associated kinase (mak) messenger ribonucleic acid expression during...

Retinol down-regulates male germ cell-associated kinase (mak) transcripts during the spermatogonial proliferation phase of spermatogenesis. Mak transcripts of 2.6- and 3.4 kb were detected in vitamin A-deficient germ cells, but decreased to undetectable levels shortly after retinol replacement to vitamin A-deficient rats. In contrast, mak seems to play a role in spermatocytes and round spermatids during meiotic and post-meiotic events. The 3.4-kb transcript initially appeared in pachytene spermatocytes and continued to increase in round spermatids; the level of the 2.6-kb transcript increased markedly only in round spermatids. These transcripts also exhibited stage-specificity in synchronized retinol-regenerated rat seminiferous tubules. Silver grains were intensely localized mainly in round spermatids in stages IV-VI of the spermatogenic cycle in normal tests after in situ hybridization. These results suggest that the mak gene in early germ cells responds to retinol in an opposite manner from the mak gene in spermatocytes or in round spermatids. The findings support the existence of two distinct pathways of retinol signaling in the testis that depend on the spatial localization and development ages of the individual germ cells.