OCCURRENCE AND FORMATION OF CYTOSKELETAL PROTEINS IN MAMMALIAN SPERMATOZOA

Mammalian spermatozoa are composed of specialized cytoskeletal element s, which appear to have no structural or protein counterparts in somat ic cells. Most evident are the outer dense fibres (ODF) and fibrous sh eath (FS) of tl-le sperm tail and the perinuclear theca (PT) of the sp erm head. The purpose of this study is to review our results on the oc currence and assembly of proteins making up these three elements durin g spermatogenesis. Our approach was to raise antibodies against the pr ominent proteins of these elements and to immunolocalize them on testi cular sections prepared for histological and ultrastructural analyses. We found that all of the cytoskeletal proteins considered were expres sed exclusively during the haploid phase of development and that the p roteins of each element had similar if not identical patterns of expre ssion. The PT proteins were synthesized in the first half of spermioge nesis and were associated with acrosome formation, while the ODF and F S proteins were synthesized in the second half of spermiogenesis. The ODF proteins assembled in a proximal-distal direction along the length of the axoneme, while the I'S proteins assembled in the opposite dire ction; both assemblies eventually meeting and overlapping within the p eriaxonemal cytoplasmic compartment. During assembly the ODF proteins appeared to be temporarily stored in granulated bodies of the cytoplas mic lobe, while the FS proteins were randomly distributed throughout t he cytoplasm. In the case of the PT, there appeared to be an interdepe ndence between PT assembly and acrosome formation. The developmental p rotein distribution patterns observed for each of the elements suggest unique cellular targeting mechanisms adapted by the spermatid to regu late the assemblies of the respective cytoskeletal proteins.