Immunochemical identification of multiple cell surface antigens appearing during specific stages of mouse spermatogenesis

Stage-specific nuclear antigen is expressed in rat male germ cells during early meiotic prophase

A germ cell nuclear antigen with approximately 44-kDa molecular weight was identified by a novel monoclonal antibody designated as Mab 2F2 from the library we have accumulated against rat testicular cells. In immature 20-day-old and adult rat testis the recognized antigen was expressed in the nuclei of early meiotic cells from preleptotene to early pachytene spermatocytes exhibiting a stage-specific appearance in the cycle of the seminiferous epithelium. The immunoreactivity was clearly associated with the meiotic chromosomes. The antigen was not detected in the late pachytene spermatocytes and more advanced stages of spermatogenesis. No labeling was observed in spermatogonia and somatic Sertoli and Leydig cells. The pattern of expression of the recognized antigen during early meiotic stages of spermatogenesis but not in mitotically dividing spermatogonia could strengthen its possible role in meiotic division.

Targeting of the domain-specific integral membrane protein PM52 to the periacrosomal plasma membrane during guinea pig spermiogenesis

The sperm plasma membrane is segregated into functionally, biochemically, and structurally distinct domains yet the protein sorting pathways and assembly mechanisms that assemble these domains during spermiogenesis are incompletely understood. We previously characterized two structurally related size-variant, integral membrane proteins of 52 kDa (PM52) and 35 kDa localized to the periacrosomal plasma membrane of guinea pig cauda epididymal spermatozoa (Westbrook-Case et al., 1994). In this study we used light and electron microscopic immunocytochemistry to define the expression pattern and sorting pathway that establishes the domain-specific distribution of PM52 during spermiogenesis. The PM52 is first expressed in acrosome-phase spermatids and it localizes exclusively to the cytoplasmic lobe. Immunoelectron microscopy revealed that both cytoplasmic vesicles and the plasma membrane of the cytoplasmic lobe labeled with anti-PM52. During early stages of expression, PM52 appeared to be absent from the head region, but significant PM52 accumulation over the spermatid head was noted in late acrosomal phase spermatids. Throughout spermiogenesis PM52 extended posteriorly to the annulus, which represents a barrier preventing PM52 diffusion into the posterior tail. Following the migration of the annulus to the midpiece-principal piece junction, PM52 began to disappear from the flagellar region and at the completion of spermiogenesis most of the PM52 was restricted to the acrosomal segment. Spermatids and epididymal sperm PM52 exhibited identical sizes by SDS-PAGE and immunoblotting, indicating that they are not proteolytically modified during epididymal maturation. The PM52 antibodies were also used to screen a guinea pig testis cDNA library, and sequence determination of full-length PM52 clones demonstrated identity of a sperm membrane protein recently termed "sperad" (Quill and Garbers, 1996). Membrane barriers and potential mechanisms establishing the domain-specific residence of PM52 are discussed.

Characterization of development-specific, cell type-specific mouse testicular antigens using testis-specific polyclonal antibodies

Antisera were raised by immunizing rabbits with mouse testicular germ cells, and absorbed in vivo by injection into castrated male whole mice to obtain a specific antiserum which reacted with mouse germ cells. The expression of mouse testis-specific antigenic macromolecules was then studied immunochemically with the antiserum. Approximately 20 antigenic macromolecules with molecular weights ranging from 26 to 110 kD were detected in the normal adult testis. At least 12 of these were differentiation-specific antigens appearing during development of germ cells, while others were expressed in testicular germ and/or somatic cells or detected only in mature spermatozoa. This technique for raising testis-specific antisera could be useful for isolation of cDNA clones encoding their antigens, as well as for investigation of the physiological roles of these molecules in germ cell differentiation at the molecular level.

Separation of round spermatids from the rat using an immunoselection panning technique

A method was devised for the isolation of round spermatids from the rat using a positive immunoselection technique (panning). A testis suspension was prepared from adult rats by enzymatic digestion of seminiferous tubules with collagenase. Specific mouse monoclonal antibody (97.25) was indirectly attached to Petri dishes and used in a panning protocol to purify spermatids from the testis cell suspension. The quantity and purity of cells isolated were determined by cell counts and histochemical (periodic acid-Schiff stain) or by immunostaining with acrosome-specific antibodies. A mean yield of 1.38 +/- 0.15 x 10(7) cells per dish was obtained with a purity of more than 90%. The viability of the cells was confirmed by epifluorescent microscopy with propidium iodide/carboxyfluorescein acetate probes. Northern blot analysis of RNA extracted directly from the dish indicated good integrity of a spermatid-specific transcript of glyceraldehyde-3-phosphate dehydrogenase (GAPDH).

Characterization of a novel spermatogenic cell antigen specific for early stages of germ cells in mouse testis

To study the mechanism of spermatogenesis during the premeiotic phase, a hybridoma producing monoclonal antibody (mAb) specific for early stages of spermatogenic cells was obtained. In immunohistochemical staining of adult testis, this mAb, designated as EE2, was able to react with type A to B spermatogonia and early meiotic cells, but not with Sertoli cells, Leydig cells, and other somatic tissues. Precursor cells of type A spermatogonia (gonocytes) were also positive for EE2 in perinatal mouse testis. The antigenic molecule recognized by mAb EE2 was a novel glycoprotein with molecular weight of 114 kDa, which had affinity with Con A and WGA lectins, and was susceptible to N-glycanase, suggesting the presence of asparagine-linked sugar chains. Furthermore, EE2 antigen was found to localize on the germ cell surface. The specific expression of this antigenic molecule suggests that it may play an important role in early spermatogenesis, of which only a little information is available at present.

Isolation and characterization of cDNA clones specifically expressed in testicular germ cells

We have cloned cDNAs involved in germ cell-specific expression. For this, a subtracted cDNA library was generated by subtracting cDNAs derived from supporting cells of mutant testis from wild-type testis cDNAs. Detailed analyses of mRNA expression revealed that the genes corresponding to the cloned cDNAs were exclusively expressed in testes and were developmentally controlled.

N-cadherin mediates Sertoli cell-spermatogenic cell adhesion

The complex topological association of Sertoli cells and spermatogenic cells in the testis suggests the existence of cell surface adhesion molecules that regulate cellular interactions within the seminiferous epithelium. The recent report of N-cadherin mRNA expression in the mouse testis implies the involvement of this known adhesion molecule in testicular cell binding. Accordingly, here we report that (1) N-cadherin is found on the surface membranes of rat spermatogenic cells and on Sertoli cells, and (2) that N-cadherin is a partial mediator of Sertoli cell-germ cell adhesion as tested in an vitro cell-cell binding assay. Antiserum directed against the N-cadherin cell adhesion recognition sequence was used for Western blot anlaysis of purified plasma membranes from Sertoli cells and from spermatogenic cells. Both membrane preparations exhibited reactivity at an appropriate M(r) of about 130 kDa. In addition, immunofluorescence assays demonstrated that both germ cells and Sertoli cells were labeled by anti-N-cadherin. Finally, the antiserum was included in a cytometer-assisted cell-cell binding test to determine its inhibitory ability. The antiserum consistently reduced specific testicular cell-cell adhesion by 30%-50%. This is the first demonstration that antibodies directed against the cadherin cell adhesion recognition sequence are capable of inhibiting cell-cell interactions. Pre-incubation of either rat Sertoli cells or spermatogenic cells alone was sufficient to achieve statistically significant inhibition of intercellular adhesion. We conclude, therefore, that N-cadherin is expressed by both Sertoli cells and spermatogenic cells and that N-cadherin is one of a number of regulatory molecules mediating local cellular associations in the mammalian seminiferous tubule.

Characterization of male meiotic germ cell-specific antigen (Meg 1) by monoclonal antibody TRA 369 in mice

We have identified a male meiotic germ cell-specific antigen (Meg 1) with monoclonal antibody (mAb) TRA 369 in mice. The Meg 1 antigen was strongly expressed in specific steps of meiotic germ cells from pachytene spermatocyte to early spermatid, and not in other germ cells or somatic cells. Immunohistochemical examination revealed that the antigen was localized to the cytoplasm and was not distributed in the nucleus or on the cell surface. This antigen was demonstrated to have a molecular weight of 93 kDa and an isoelectric point of 5.2 by Western blotting. This molecule was first detected in the testis of 13-day-old mouse when pachytene spermatocytes first appeared. Thus this is a differentiation-specific antigen in male meiotic germ cells, and mAb TRA 369 is a useful tool to study the regulation of germ cell differentiation and to define germ cell development in a molecular level.

Sperm antibodies

Anti-sperm antibodies (ASA) occur in 1% to 30% of infertile couples. Mechanisms by which ASA impair fertility include prevention of fertilization by decreasing acrosome reaction and/or zona pellucida binding, and postfertilization effects. Treatment for ASA involves assisted reproductive technologies.

Localization of post-vasectomy sperm autoantigens in the Lewis rat

Major rat sperm autoantigens of 86, 63, 43, 28 and 20 kDa are recognized by post-vasectomy and hyperimmunization antisera from the Lewis rat (Handley et al., Biol. Reprod. 39 (1988) 1239-1250). In the present study, affinity purified monospecific isoantibodies to each autoantigen were produced by elution from antigens which had been separated by SDS-PAGE and transferred to nitrocellulose. Western blot analysis confirmed a singular specificity for the 63, 28 and 20 kDa antisera and demonstrated some cross reactivity between the 86 kDa and the 43 kDa antisera. The polyclonal antiserum from which the monospecific antisera were produced stained the entire spermatozoon, while monospecific antibodies bound only to the sperm tail, staining the proximal portion (43 and 28 kDa), a distal domain (63 kDa), or the entire tail (86 kDa). Immunohistochemically stained sections of normal rat testes revealed that the 63, 43 and 28 kDa autoantigens were synchronously expressed in the cytoplasm of spermatids in the apical portions of seminiferous tubules during stages II-VIII in the cycle of the seminiferous epithelium. The 86 kDa autoantigen showed little or no staining in testis sections, implying that this autoantigen appeared on mature sperm following spermiation. These and other data suggest that a highly polymeric structure, possibly within the outer dense fibers of the tail, is a dominant sperm autoimmunogen following vasectomy of the Lewis rat.

Spatial and temporal expression of cell surface galactosyltransferase during mouse spermatogenesis and epididymal maturation

We have previously shown that sperm-egg recognition in the mouse is mediated by the binding of galactosyltransferase (GalTase) on the sperm surface to its appropriate glycoside substrate in the egg zona pellucida [L. C. Lopez, E. M. Bayna, D. Litoff, N. L. Shaper, J. H. Shaper, and B. D. Shur (1985) J. Cell Biol. 101, 1501-1510]. In the present study, we have defined the spatial and temporal expression of surface GalTase during spermatogenesis and epididymal maturation. Purified populations of spermatogenic cells were isolated by unit gravity sedimentation, and surface GalTase expression was determined by indirect immunofluorescence and by direct enzymatic assay. GalTase is present on the surface of all spermatogenic cells assayed. During differentiation, there is a progressive redistribution of GalTase from an initially diffuse and uniform localization on the surface of primary spermatocytes to a restricted plasma membrane domain overlying the dorsal aspect of the mature acrosome. This apparent redistribution of surface GalTase was confirmed by direct enzymatic assays, which show that surface GalTase activity, normalized per cell, remains relatively constant throughout spermatogenesis, despite a drastic reduction in cell surface area. When normalized to the relevant cell surface area, the GalTase concentration per square micrometer increases 77-fold from pachytene spermatocytes to cauda epididymal sperm. Cell surface GalTase is thought to be a cytoskeletally associated transmembrane protein [N. L. Shaper, P. L. Mann, and J. H. Shaper (1985) J. Cell Biochem. 28, 229-239]; consequently we examined whether cytoskeletal components may be involved in the redistribution of GalTase during spermatogenesis. beta-Tubulin, monomeric actin, and filamentous actin were found to be present during spermatogenesis, as assayed by indirect immunofluorescence and by Western immunoblotting. alpha-Actinin and vinculin were not detectable under these conditions and served as negative controls. During spermatogenesis, the distribution of tubulin coincides with the appearance of the mitotic spindle, flagellum, and manchette. On the other hand, the distribution of filamentous actin coincides with surface GalTase, suggesting that actin-containing microfilaments may participate in the redistribution of surface GalTase during spermatogenesis.