Biogenesis of specialized cytoskeletal elements of rat spermatozoa.

Our results on the formation of the ODF and perforatorium are diagrammatically summarized in Figures 30 and 31. The developmental expression of proteins making up these two cytoskeletal elements differs in timing, duration and intracellular localization. The ODF proteins are synthesized exclusively during the latter part of spermiogenesis, well after transcriptional activity in the haploid germ cell nucleus has ended. This implies that these major integral proteins of the tail are translationally regulated and that mechanisms must exist for the storage and eventual release of the mRNAs encoding these proteins. The perforatorial proteins, on the other hand, begin to be synthesized during the meiotic prophase reaching a peak of production in early spermiogenesis just before the initiation of the condensation of the spermatid's nucleus, at which time RNA synthesis stops. Another major difference between ODF and perforatorial protein production is that there seems to be a coordinated activity between the synthesis and the assembly of the ODF proteins, whereas there appears to be an almost 25 day delay between the initial meiotic synthesis and final condensation of perforatorial proteins in the subacrosomal space at the end of spermiogenesis. As for the intracellular localization of ODF and perforatorial proteins both have unprecedented distributions. The ODF proteins appear to be concentrated in a particular type of granular body which is especially abundant in the elongated spermatid at the time of peak ODF assembly. The perforatorial proteins, on the other hand, appear to be concentrated in the nuclei of pachytene spermatocytes and round spermatids until their displacement into the cytoplasm during nuclear condensation. Both forms of localization suggest a storage role for these proteins uniquely adapted by the spermatid to regulate the assemblies of the respective cytoskeletal elements.