Search

An mRNA with a substantial similarity to the rat p62 mRNA that encodes a nucleoporin was cloned from the rat testis. A probe derived from a unique sequence in the nucleoporin-related (NPR) cDNA revealed a novel mRNA of 1.3 kb, different from the 2.7-kb transcript attributed to the p62 gene. This 1.3-kb transcript was not detected in Sertoli cells; it was found primarily in the haploid germ cells of the adult testis. The DNA sequencing revealed that the central region of the NPR cDNA sequence was identical to the 3' portion of the p 6 2 cDNA containing heptad repeat sequences. However, the 5' region and the extreme 3' region of the NPR cDNA sequence were different from the p62 cDNA. Interestingly, the extreme 3' untranslated region (UTR) contained a 212-bp inverted repeat of a sequence located in the middle of the NPR cDNA that is identical to the p62 sequence. The inverted repeats of the NPR sequence could potentially hybridize, leading to the formation of circular transcripts. Using antibodies specific for the C-terminal regions of p62, a 26-kDa protein was detected from NPR cDNA hybrid-arrested translational products, and a 28-kDa protein was detected from the testis germ cell extracts but not from Sertoli cell extracts.

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 testes 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 developmental ages of the individual germ cells.