Basic proteins of the perinuclear theca of mammalian spermatozoa and spermatids: a novel class of cytoskeletal elements.

Abstract

Abstract. The nuclei of bovine spermatids and spermatozoa are surrounded by dense cytoplasmic webs sandwiched between the nuclear envelope and the acrosome and plasma membrane, respectively, filling most of the cytoplasmic space of the sperm head. This web contains a complex structure, the perinuclear theca, which is characterized by resistance to extractions in nondenaturing detergents and high salt buffers, and can be divided into two major subcomponents, the subacrosomal layer and the postacrosomal calyx. Using calyces isolated from bull and rat spermatozoa we have identified two kinds of basic proteins as major constituents of the thecal structure and have localized them by specific antibodies at the light and electron microscopic level. These are an Mr 60,000 protein, termed calicin, localized almost exclusively to the calyx, and a group of multiple-band polypeptides (MBP; Mr 56,000-74,000), which occur in both the calyx and the subacrosomal layer. The polypeptides of the MBP group are immunologically related to each other, but unrelated, by antibody reactions and peptide maps, to calicin. We show that these basic cytoskeletal proteins are first detectable in the round spermatid stage. As we have not detected any intermediate filament proteins and proteins related to nuclear lamins of somatic cells in sperm heads, we conclude that the perinuclear theca and its constituents, calicin and MBP proteins, are the predominant cytoskeletal elements of the sperm head. Immunologically cross-reacting polypeptides with similar properties have been identified in the heads of rat and human spermatozoa. We speculate that these insoluble basic proteins contribute, during spermiogenesis, to the formation of the perinuclear theca as an architectural element involved in the shape changes and the intimate association of the nucleus with the acrosome and the plasma membrane.URING the past decade it has become increasingly clear that the overall shape of a cell and its internal architecture is dependent not only on membranous elements but also on a group of structures that resist cell lysis and extraction by nondenaturing detergents and buffers of various pH and ionic strength. Such proteinaceous structures are now usually referred to under the collective terms cytoskeleton, as to the cytoplasm, and karyoskeleton, for nuclear architectural elements. Among the cytoskeletal components some of the most prominent structures are the actin-containing microfilaments and the tubulin polymers, i.e., microtubules. The term cytoskeleton also includes certain filamentous webs such as membranous coats in the cell periphery, many of which contain proteins of the spectrin family, the regular clathrin coats of coated pits and vesicles, and the plaques of adhering junctions. Remarkably, some residual cyto-and karyoskeletal components are preserved even after extraction in high salt concentrations, and maintain typical architectural features. Structures of this category include the intermediate-sized filaments (IFs) ~ of the cytoplasm and the bio...

Somatic Histones Are Components of the Perinuclear Theca in Bovine Spermatozoa

“…To date, all characterized PT proteins share a resistance to non-ionic detergents, such as Triton X-100, and to extraction by high salt (16). High pH buffers (NaOH), or the combination of a reducing agent with a denaturing detergent, are required for their complete removal and/or migration through SDS-PAGE (3).…”

Immunochemical Characterization of a Human Sperm Fibrous Sheath Protein, Its Developmental Expression Pattern, and Morphogenetic Relationships with Actin

“…However, few antibodies directed against proteins of several classes of somatic IFs recognize the FS in sperm cells (Eddy et al 1991;Longo et al 1987;Franke et al 1979), including an anti-neurofilament antibody (Jassim 1991;Jassim et al 1991). Moreover, characterization of the Fsc1 cDNA, possibly coding for the mouse M r 78-80 ϫ 10 3 major FS polypeptide, reveals no significant homology with other known cytoskeletal proteins, except for a region with Ͼ44% identity with a stretch of a centromeric protein-E (CENP-E) (Fulcher et al 1995).…”

Sperm head shaping in ratites: New insights, yet more questions

“…During spermiogenesis the PT manifests as a continuous layer of detergent resistant material that covers the entire surface of the nucleus with the exception of the implantation fossa and can be subdivided into a sub-acrosomal layer (SAL) and a post-acrosomal sheath (PAS) or calyx (Clermont et al, 1993;Longo et al, 1987;Oko, 1995;Oko and Sutovsky, 2009;Toshimori, 2003;Tovich et al, 2004). The PT is composed of a variety of cytosolic and nuclear proteins (Dadoune, 2003;Longo et al, 1987;Meistrich, 1993;Oko and Sutovsky, 2009;Toshimori, 2003) which, together with the specific location of the theca, would suggest that it serves to bind the acrosome and post-acrosomal plasmalemma to the nucleus, thereby assisting in maintaining the shape of the sperm head (Longo and Cook, 1991).…”

“…The PT is composed of a variety of cytosolic and nuclear proteins (Dadoune, 2003;Longo et al, 1987;Meistrich, 1993;Oko and Sutovsky, 2009;Toshimori, 2003) which, together with the specific location of the theca, would suggest that it serves to bind the acrosome and post-acrosomal plasmalemma to the nucleus, thereby assisting in maintaining the shape of the sperm head (Longo and Cook, 1991). Accentuating this role of the PT is the observation that failure of the PT to form correctly results in the formation of acrosomeless round-headed human sperm (Escalier, 1990).…”

“…The precise alignment and repeatability of the finger-like elaborations of the PAS is suggestive of a mechanical role for this structure. However, the composition of the nuclear and cytosolic proteins making up the avian PAS, as determined for mammals (Longo et al, 1987;Meistrich, 1993;Oko, 1995;Tovich et al, 2004;Oko and Sutovsky, 2009) remains to be resolved before a more meaningful conclusion on the role of this structure can be arrived at.…”