In situ localization of spermatogenic cell-specific glyceraldehyde 3-phosphate dehydrogenase (Gapd-s) messenger ribonucleic acid in mice.

Northern blot analysis with a cDNA clone for mouse spermatogenic cell-specific glyceraldehyde 3-phosphate dehydrogenase (Gapd-s) previously identified transcripts in isolated round spermatids, but not in isolated pachytene spermatocytes, strongly suggesting that Gapd-s transcription first occurs in haploid germ cells. In the present study, in situ hybridization was carried out with a [35S]-labeled anti-sense RNA probe of Gapd-s to define more precisely the temporal expression and spatial distribution of Gapd-s mRNA in adult mouse testes. Gapd-s transcripts were not detected in spermatogonia, primary spermatocytes, secondary spermatocytes, or spermatozoa. However, they were abundant in round spermatids and condensing spermatids. Transcripts were not detected in somatic cells of the testis, in oocytes in pre-antral or antral follicles, or in skeletal muscle. Grain counts were used to define when the Gapd-s gene was expressed during round spermatid development in adult mice. The number of silver grains first exceeded background levels in step 4-6 spermatids (early cap phase of spermiogenesis) and were high in step 7-15 spermatids (acrosome and elongation phases of spermiogenesis). However, they returned to background levels in step 16 spermatids, the final step of spermiogenesis in the mouse. In 20-day-old juvenile mice, Gapd-s transcripts were first detected in round spermatids during the early cap phase of development. These observations confirmed that Gapd-s mRNA is expressed during the post-meiotic phase of male germ cell development, demonstrated that Gapd-s transcripts are present in step 4-15 spermatids, and established that transcription begins in round spermatids during the early cap phase of spermiogenesis in both juvenile and adult mice.