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 results 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 that N-terminus. Recombinant GAPD-S protein Backing 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 rightly associated with the fibrous sheath of the flagellum, consistent with a potential role in regulating sperm motility.