AJ-p97: a novel antigen of the human sperm tail fibrous sheath detected by a neurofilament monoclonal antibody

Electron microscopic observations of human sperm whole-mounts after extraction for nuclear matrix and intermediate filaments (NM-IF)

The extraction for nuclear matrix and intermediate filaments (NM-IF) is used to reveal, isolate and study these highly resistant structures in different cell types. We applied for the first time this chemical dissection to human spermatozoa and observed them as whole-mounts by unembedded electron microscopy. The general appearance of NM-IF extracted sperm cells was preserved, showing the intermediate filament-like properties of their cytoskeletal components. In most heads, a network was observed in subacrosomal position, consisting of hubs interconnected by filaments. It seemed to be overlaid on another, finer network. The neck retained its integrity, allowing observations of the three-dimensional structure of the segmented columns. More distally, axoneme and outer dense fibres were covered by submitochondrial cytoskeleton in the middle piece and fibrous sheath in the principal piece, with the annulus usually detached from the fibrous sheath. End piece microtubules were retained in most cells and showed a tendency of cohesion, remaining in a parallel bundle or forming flat sheets. In conclusion, our results provided additional structural details of human sperm cytoskeleton and demonstrated the advantages of combining different methodological approaches in ultrastructural research.

Characterisation of fibrous sheath and midpiece fibre network polypeptides of marsupial spermatozoa with a monoclonal antibody

In this study cytoskeletal antigens common to brushtail possum and tammar wallaby spermatozoa were characterised using a monoclonal antibody (PSA-10). Using indirect immunofluorescence, the PSA-10 antibody detected antigens predominantly associated with the midpiece and principal piece of mature, permeabilised marsupial spermatozoa. The principal piece determinant, shared by a variety of other species, was found to arise in the marsupial testis. Midpiece localisation of the PSA-10 epitope was detected only in marsupial spermatozoa and shown to arise in the epididymis. Immunogold labelling demonstrated that the PSA-10 antigens were predominantly associated with the fibrous sheath and midpiece fibre network of both possum and wallaby spermatozoa. Western blotting suggested that two major possum and wallaby sperm polypeptides of 158 and 182 kDa were associated with the midpiece fibre network, a cytoskeletal structure unique to marsupial spermatozoa. A 32 kDa polypeptide was associated with the principal piece fibre network and/or fibrous sheath. The finding that these marsupial sperm cytoskeletal proteins share a common linear epitope suggests that they share some sequence similarity. The midpiece fibre network of marsupial sperm, like the fibrous sheath, has been proposed to have a structural role in providing passive stiffening for the flagellum (Harding et al., 1975, 1979; Olsen, 1975). The PSA-10 monoclonal antibody may provide a tool for comparative studies of mammalian sperm cytoskeletal proteins, particularly the marsupial midpiece fibre network. It may also allow the formation of this unique marsupial cytoskeletal structure, and its fate during the fertilisation process, to be followed by immunological means.

Immunochemical characterization of a human sperm fibrous sheath protein, its developmental expression pattern, and morphogenetic relationships with actin

Among the monoclonal antibodies (MAbs) prepared against human sperm extracts, MAb 4F7 was found to be specific to the human and Macaca fascicularis sperm cytoskeletal fibrous sheath (FS). In Western blotting, MAb 4F7 stains a doublet of polypeptides of about M(r) 95 x 10(3) in extracts of human sperm cells. These polypeptides are not recognized by the KL1 anti-cytokeratin MAb, nor by the MAbs known to bind to the carboxy terminal (IFA) and to the amino terminal (ME101) rod domain of intermediate filaments. Sequential extraction procedures shows that the FS polypeptides recognized by MAb 4F7 are exposed after treatment with 8 M urea 4F7 immunoreactivity is lost after treatment with high ionic solutions (NaCl; KCl, Kl). Immunogold electron microscopy reveals that this protein is present throughout the FS. This FS antigenic determinant first accumulates in an FS proximal body in late spermatids, then in granules extending distally along the flagellum. Staining of spermatozoa with flagellar dysgenesis reveals that this FS protein colocalizes with actin no matter what the location of their abnormal assembly. These data suggest that the transient microtubule-like spindle-shaped body of as yet unknown function could be involved in FS protein deposition and that the assembly of the FS and actin could be under the control of some common morphogenetical factor(s). MAb 4F7 should allow further investigations of this peri-axonemal structure in both normal and pathological conditions.

Identification of a 53-kDa antigen in the fibrous sheath of avian spermatozoa

The intracellular fibrous sheath that surrounds the proximal part of the sperm flagellar axoneme in non-passerine birds is structurally different from that of mammals. We raised a monoclonal antibody against the fibrous sheath of cockerel spermatozoa by in vitro immunisation. Indirect immunofluorescence and immunogold labelling showed that the antibody bound specifically to the fibrous sheath. It also labelled the fibrous sheath in quail spermatozoa. In both species the antibody bound an antigen that had a molecular weight of about 53 kDa. In tissue sections from adult cockerel testis the antigen was located in spermatids and spermatozoa with little cross-reactivity with the basal region of the seminiferous epithelium or interstitial tissue. The antibody may prove to be a useful tool in studies of avian spermiogenesis.

Impaired antibody diffusion within the cytoplasmic membrane-fibrous sheath interspace of the human sperm tail

Monoclonal and polyclonal antibodies specific for the fibrous sheath (FS) were used to assess their diffusion within the subcytoplasmic membrane space of the human sperm tail. Using indirect immunofluorescence (IIF) and immunogold electron microscopy (IEM), the staining of the entire FS with these antibodies was observed only when the spermatozoa were completely demembranated by detergents or dried onto slides. Partial damage to sperm cytoplasmic membranes by freezing and thawing resulted in segmental staining of the FS. The IEM of such spermatozoa with the antibodies revealed the distribution of gold particles on the FS in denuded areas only and adjacent segments which retained their cytoplasmic membrane were not stained. These results indicate that partial disruption of the sperm plasma membranes does not lead to free diffusion of antibodies within the cytoplasmic membrane-FS interspace. This property appears to be unique to sperm cells and is due to their specialized structural organization.

Antigenic determinants of human sperm tail fibrous sheath proteins

Mouse anti-fibrous sheath antisera (MAFA) produced by immunizing mice with purified preparations of human sperm tail fibrous sheath (FS) reacted with the principal piece of less than 10% of freshly isolated spermatozoa which were immotile and probably dead. Following their demembranation by detergents or repeated freezing and thawing, all spermatozoa were stained. This was also demonstrated on spermatozoa dried onto slides, but the undiluted xenoantisera showed additional reactivity with the acrosomal zone (AZ). Using immunogold electron microscopy, the target antigens were ultrastructurally localized to the FS, and a few spermatozoa showed some reaction at the AZ subacrosomal perinuclear theca. Following titration of the antibodies, the anti-AZ-reaction became undetectable at a dilution of 1:20 while their reactivity with the principal piece continued to a 1:400-dilution. These results indicated that the xenoantisera probably contained an additional unrelated antibody component which reacted with the AZ. Western blotting and staining of purified FS with MAFA detected seven major protein bands with MW ranging between 25 kDa and 97.4 kDa. In human testes, the 1:50 diluted MAFA reacted with sperm tails only, indicating the late expression of the antigenic determinants during spermatogenesis. MAFA did not react with oesophagus, stomach, duodenum, ileum, nasal lining tissues, uterus, pericardium, pancreas, thyroid gland, or cultured fibroblasts. The xenoantisera did, however stain the skin epidermis and cultured keratinocytes which exhibited filamentous cytoplasmic staining although their target antigens could not be biochemically identified. These results indicate that the FS proteins express antigenic determinants which are not shared with other cytoskeletal elements within the sperm flagellum or a variety of somatic tissues.

AJ-p90: a novel protein of the perinuclear theca in human sperm subacrosome

A perinuclear theca protein of the human sperm subacrosome was detected using LH43 monoclonal antibody which was originally raised against human keratinocytes. Using indirect immunofluorescence, the antibody stained the acrosomal zone (AZ) of dried ejaculated spermatozoa but did not react with viable cells, thus suggesting that the antigen was intracellular. This was confirmed by immunogold electron microscopy which also revealed the ultrastructural localisation of the antigen to the subacrosomal fibrils. Throughout spermatogenesis the antigen was only detected on the AZ of developed testicular spermatozoa and its expression was continued during their epididymal passage. Biochemically, the protein was insoluble in Triton, and dithiothreitol (DTT) was required for its solubilisation. In Western blotting of sperm and keratinocyte lysates, the antibody detected similar 90-kDa protein doublets (AJ-p90). These biochemical features exclude the identity of AJ-p90 with various cyto- and karyo-skeletal antigens, including the intermediate filaments and microfilaments. AJ-p90 therefore represents a novel product of the subacrosomal perinuclear theca. The significance of these data is discussed together with the importance of the antibody for probing the perinuclear theca in normal and abnormal germ cells, including multinucleated spermatids which also showed reactivity with the antibody.