Glyceraldehyde 3-phosphate dehydrogenase-S protein distribution during mouse spermatogenesis

The spermatogenic cell-specific isoform of glyceraldehyde 3-phosphate dehydrogenase (GAPD-S) may regulate glycolysis and energy production required for sperm motility. Although the steady-state level of Gapd-s mRNA is maximal at step 9 of mouse spermatogenesis, GAPD-S protein was not detected by immunohistochemistry until steps 12-13. This result suggests that Gapd-s is translationally regulated. Western blot analysis of isolated germ cells confirmed that GAPD-S is not detected in pachytene spermatocytes or round spermatids. A major immunoreactive protein migrating with a molecular weight (M(r)) of 69,200 was observed in condensing spermatids and cauda sperm. Additional minor proteins that migrated at M(r) 55,200, 32,500, and 27,500 were detected in sperm. The molecular weight of GAPD-S is higher than the predicted molecular weight of 47,445, apparently due to a proline-rich 105-amino acid domain at the N-terminus. Recombinant GAPD-S protein lacking the proline-rich region migrated at M(r) 38,250, comparably to somatic GAPD, which also lacks the proline-rich domain. Indirect immunofluorescence demonstrated that GAPD-S is restricted to the principal piece in the sperm flagellum. Western blot analysis indicated that GAPD-S is tightly associated with the fibrous sheath of the flagellum, consistent with a potential role in regulating sperm motility.