Fine structural localization of Concanavalin A binding sites on hamster spermatozoa

Penetration of concanavalin-A-treated Chinese hamster oocytes by golden hamster spermatozoa in vitro, and chromosome analysis of hybrid 1-cell zygotes

Pretreatment of zona-free Chinese hamster (CH) oocytes with three kinds of lectin--concanavalin A (Con-A), phytohaemagglutinin-P (PHA) and wheat germ agglutinin (WGA)--was attempted in order to improve penetration by golden hamster (GH) spermatozoa in vitro. Con-A had no significant effect on penetration at 2 micrograms/ml, adequately facilitated oocyte-sperm fusion at 4 micrograms/ml, and caused excessive sperm binding and resultant severe polyspermy at 10 micrograms/ml. Neither PHA nor WGA had positive effects on sperm penetration at any concentrations (2-10 micrograms/ml) examined. Using the Con-A (4 micrograms/ml) pretreatment, high rates of interspecific fertilisation and subsequent chromosome analysis of hybrid 1-cell zygotes were achieved. Among 258 CH oocytes used, 212 (82.2%) were fertilised and 153 (72.2% of fertilised ova) developed to the first cleavage metaphase. Eventually, 132 CH-derived chromosome complements and 153 GH-derived ones were successfully karyoanalysed. Incidences of aneuploidy and structural anomaly were 3.1% and 2.3% in CH complements, and 1.4% and 6.5% in GH complements, respectively. These incidences were not significantly different from those obtained by intraspecific in vivo fertilisation, suggesting that our interspecific in vitro fertilisation system does not cause chromosome aberrations.

Plasma membrane alterations of maturing goat (Capra indicus) spermatozoa: lectin-binding and freeze-fracture study

A qualitative and quantitative analysis of lectin-binding sites has been undertaken on spermatozoa recovered from different regions of the epididymis of the goat (Capra indicus) using fluorescein isothiocyanate-linked lectins (Bauhinia purpurea BPA, Concanavalin A Con A, Dolichos biflorus DBA, Maclura pomifera MPA, Arachis hypogaea or peanut agglutinin PNA, Glycine max or soyabean agglutinin SBA, Ulex europaeus UEA, and Triticum vulgaris or wheat-germ agglutinin WGA), in conjunction with scanning and transmission electron microscopy, and freeze-fracture techniques. Flow cytometric analysis has also been used to quantitize binding affinity. Spermatozoa from caput to cauda epididymidis show no significant variation in lectin-binding ability, but the samples removed from the corpus epididymidis contain a greater number of binding sites. The passage of spermatozoa through the epididymidis is accompanied by a redistribution of the plasma membrane lectin-receptors covering the sperm head and tail. Receptors for BPA, DBA, PNA and SBA are specifically restricted to the anterior region of the acrosome in caudal spermatozoa. Freeze-fracture replicas, examined to study changes in organisation of intramembranous particles of the plasma membrane during sperm maturation, reveal distinct changes in their distribution in the acrosome, post-acrosome and spermatozoon tail, especially in the corpus and cauda epididymidis.

Changes in the distribution of intramembranous particles and filipin-reactive membrane sterols during in vitro capacitation of golden hamster spermatozoa

Membrane alterations accompanying in vitro capacitation of hamster spermatozoa were examined using the freeze-fracture technique with or without use of filipin, a sterol-binding probe. In the spermatozoa prior to or at 10 min after start of incubation in capacitating medium, large (about 11 nm) and small (8-9 nm) intramembranous particles (IMPs) were present in the periacrosomal region of the sperm plasma membrane (PAPM). Filipin sterol complexes (FSCs) were densely (about 500/micron 2) distributed in the PAPM prior to incubation. The density of FSCs in the PAPM was reduced by 70-80% of the original density by 2 hr of incubation. At the same time, small patches of IMP-free areas appeared in the plasma membrane above the equatorial and middle segments of the acrosome. By the end of 3 hr of incubation, the majority of small IMPs had disappeared from the PAPM. Remaining large and small IMPs tended to aggregate in the PAPM. During incubation in capacitation medium, "cords," or linear arrangements of closely packed IMPs, appeared near the posterior ring of the sperm head. These observations strongly suggest that the acrosome reaction of the hamster spermatozoa is preceded by the removal (deletion) of filipin-reactive sterols (FRSs) and the disappearance of small IMPs from the lipid bilayer of PAPM.

Changes in the distribution of intramembranous particles and filipin-sterol complexes during epididymal maturation of golden hamster spermatozoa

Golden hamster spermatozoa in various segments of the excurrent duct system were studied by freeze-fracture with and without filipin treatment. Two types of regular IMP (intramembranous particle) patterns temporarily appear on the plasma membrane covering the sperm head. One is a hexagonal arrangement seen in the acrosomal region, and the other is a linear arrangement near the posterior ring. Both patterns are seen in the spermatozoa from the corpus epididymidis. The FSC (filipin-sterol complex) density in the plasma membrane covering the acrosome increases from about 400 to 500 FSC/microns2 during epididymal passage. In this region, the majority of the membrane sterols appears to reside on the outer leaflet of the lipid bilayer. When the spermatozoa reach the cauda epididymidis, FSCs in the outer acrosomal membrane virtually disappear from the apical segment, while they increase in the middle segment (250 FSC/microns2). These observations are discussed in relation to epididymal maturation.

Purification and characterization of two plasma membrane domains from ejaculated bull spermatozoa

Plasma membranes were detached from ejaculated bull spermatozoa by a brief sonication in a moderately hypotonic medium, and the released plasma membranes were partially purified by differential centrifugation. The resulting fraction was enriched 8- and 15-fold in alkaline phosphatase and 5' nucleotidase activities, respectively, compared with the starting sonicated spermatozoa. This total plasma membrane fraction was separated into two distinct fractions by equilibrium density centrifugation on a continuous linear sucrose gradient. Two peaks of light scattering material were formed at densities of 1.117 and 1.148 g/ml. The denser peak contained most of the protein of the plasma membrane fraction, whereas nearly all the concanavalin A binding activity was found in the lighter peak. The two bands had distinctly different polypeptide compositions when analyzed by SDS PAGE. Polyclonal antibodies were raised in rabbits against a major integral membrane glycoprotein of each fraction (Mr of 92,000 in the light peak and 98,000 in the dense peak). The two antigens were detected on the surface of intact spermatozoa by indirect immunofluorescence microscopy. The 92-kD protein (present in the lighter band) was detected only on the plasma membrane of the acrosomal and anterior postacrosomal regions of the head. The 98-kD antigen, present in the heavier band, was localized to the surface of the postacrosomal region of the head, to the principal piece of the tail, and to the connecting piece between the head and tail. The exclusive localization of the 92-kD polypeptide to the surface of the anterior portion of the head was confirmed by immunoelectron microscopy. These data show that the two fractions isolated on the sucrose gradient originate from different regions of the sperm cell plasma membrane.

The acrosomal membrane of boar sperm: a Golgi-derived membrane poor in glycoconjugates

The acrosome is a large secretory vesicle of the sperm head that carries enzymes responsible for the digestion of the oocyte's investments. The event leads to sperm penetration and allows fertilization to occur. Release of the acrosomal enzymes is mediated by the interaction between sperm acrosomal and plasma membranes (acrosome reaction). Biochemical characterization of the acrosomal membrane has been restrained by a lack of methods to isolate uncontaminated fractions of the membrane. Here, we use new methods to expose the membrane to in situ cytochemical labeling by lectin-gold complexes. We study the topology and relative density of glycoconjugates both across and along the plane of the acrosomal membrane of boar sperm. Detachment of the plasma membrane from glutaraldehyde-fixed cells exposed the cytoplasmic surface of the acrosome to the lectin markers; freeze-fractured halves of the acrosomal membrane were marked by "fracture-label" (Aguas, A. P., and P. Pinto da Silva, 1983, J. Cell Biol. 97:1356-1364). We show that the cytoplasmic surface of the intact acrosome is devoid of binding sites for both concanavalin A (Con A) and wheat germ agglutinin (WGA). By contrast, it contains a high density of neuraminidase-resistant anionic sites detected by cationic ferritin. On freeze-fractured sperm, the receptors for Con A partitioned with the exoplasmic membrane half of the acrosomal membrane. The Con A-binding glycoconjugates were accumulated on the equatorial segment of the membrane. A low density of WGA receptors, as well as of intramembrane particles, was found on the freeze-fracture halves of the acrosomal membrane. The plasma membrane displayed, in the same preparations, a high density of receptors for both Con A and WGA. We conclude that the acrosome is limited by a membrane poor in glycoconjugates, which are exclusively exposed on the exoplasmic side of the bilayer. Regionalization of Con A receptors on the acrosome shows that sperm intracellular membranes, like the sperm surface, express domain distribution of glycocomponents.

Lectin-coated agarose beads in the investigation of sperm capacitation in the hamster

Sperm surface changes during in vitro capacitation were examined with the help of an assay system using lectin-coated agarose beads. The nature and intensity of binding of epididymal spermatozoa to beads depended entirely on the particular stage of capacitation and the type of lectin attached to the bead surface. Fresh epididymal spermatozoa bound readily to beads coated with Con A, LCA, WGA, and PNA, but not with seven other lectins. During capacitation there was a constant decline in sperm binding to beads, and spermatozoa cultured for 4-5 hr bound only to those coated with Con A. A dramatic increase in sperm binding to Con A-coated agarose beads occurred between 4.5 and 5 hr, when large numbers of hyperactivated spermatozoa adhered, predominantly through their flagellae, to form large clumps on the beads. The clumping of spermatozoa on Con A-coated beads was enhanced in the presence of stimulators of capacitation (i.e., taurine, hypotaurine, and phosphodiesterase inhibitors) and was suppressed in the presence of various metabolic inhibitors (i.e., sodium azide and local anesthetics). The implications of these results are that the carbohydrate components of the entire surface of spermatozoa undergo striking changes during capacitation, and a close relationship may exist between the sperm surface and the metabolic changes occurring within capacitating spermatozoa. Sperm-bead binding assays are clearly able to recognize surface changes in asynchronous populations of motile spermatozoa and, due to their simplicity and speed, should prove to be valuable in gaining a greater understanding of the biochemistry of sperm capacitation.

Regionalization of transmembrane glycoproteins in the plasma membrane of boar sperm head is revealed by fracture-label

We used fracture-label and surface labeling techniques to characterize the distribution and topology of wheat germ agglutinin (WGA) receptors in the plasma membrane of boar sperm heads. We show that freeze-fracture results in preferential, but not exclusive, partition of WGA-binding sites with the outer (exoplasmic) half of the plasma membrane. Labeling of the inner (protoplasmic) half of the membrane is significant, and is denser over the areas that overlie the acrosome. Exoplasmic membrane halves are uniformly labeled. Analysis of freeze-fracture replicas revealed that the distribution of intramembrane particles over protoplasmic faces parallels that of WGA-binding sites as observed by fracture-label. Coating of intact spermatozoa with cationized ferritin results in drastic reduction of the labeling of both protoplasmic and exoplasmic membrane halves. Labeling of sperm cells lysed by short hypotonic shock fails to reveal the presence of WGA-binding sites at the inner surface of the plasma membrane. We conclude that: (a) all WGA-binding glycoconjugates are exposed at the outer surface of the membrane; (b) some of these glycoconjugates correspond to transmembrane glycoproteins that, on fracture, partition with the inner half of the membrane; (c) these transmembrane proteins are accumulated in the region of the plasma membrane that overlies the acrosome; and (d) parallel distribution of intramembrane particles and WGA-binding glycoproteins provides renewed support for the view of particles as the morphological counterpart of integral membrane proteins.

Characterization of lectin receptors isolated from the outer acrosomal membrane of boar spermatozoa

The outer acrosomal membrane (OAM) of boar spermatozoa was isolated by homogenization and centrifugation through modified colloidal silica. Homogeneity of the isolated membrane fraction (OAM) was revealed by transmission electron microscopy. At least 10 protein components could be discriminated by SDS-PAGE electrophoresis of the OAM, with molecular weights ranging from 340 to 15 kdal. Radiolabelling of the externally disposed carbohydrate side-chains by [3H]borhydride reduction of the isolated membrane, oxidized by use of galactose oxidase, revealed one main galactoprotein with a reduced molecular weight of about 270 kdal. This was identified as the RCA-120 receptor protein by means of lectin-affinity chromatography, high resolution gelfiltration and SDS-PAGE. Screening of the Con A binding properties of the solubilized membrane components partially isolated by affinity chromatography and HPLC was performed by an enzyme-linked-lectin-assay (ELLA). Electrophoretic analysis including a Con A-peroxidase staining procedure allowed the identification of 4 Con A binding proteins of the OAM with molecular weights of 120, 110, 88 and 66 kdal.

The acrosomal membrane system of boar spermatozoa--morphological and biochemical studies

The distribution of the cell surface saccharides with alpha-glycosidically linked mannose and terminal galactose was displayed by fluorescence microscopical examinations with FITC-conjugated concanavalin A and Ricinus communis agglutinin-120. The lectin binding sites of the inner cellular membranes--inner and outer acrosomal membrane--were ultrastructurally localized by electron microscopical studies using the lectin-peroxidase technique. It could be demonstrated that both acrosomal membranes contain covalently bound carbohydrates. In order to characterize the acrosomal membrane components which are responsible for the binding to lectins, the outer acrosomal membrane was separated after homogenization by centrifugation through modified colloidal silica. The exposed membrane proteins were labelled by galactose oxidase mediated introduction of tritium into the carbohydrate side chains of the glycoproteins. After solubilization the membrane components were analysed by affinity chromatography and electrophoresis. For a general characterization the cholesterol/phospholipid ratio of ejaculated boar spermatozoa and the isolated membrane fraction was determined and some enzymatic activities were assessed.

Lectins as probes of the spermatozoon surface

Studies involving the use of lectins to probe the spermatozoon surface are reviewed, with particular emphasis on mammalian spermatozoa and their various transformations during maturation, capacitation, and the acrosome reaction. Although the numbers of lectin bindings sites on spermatozoa are generally comparable to those of many somatic cells, the distribution of most lectins thus far studied is highly restricted to certain domains of the cell surface. These domains are often related to specific underlying morphological entities such as the acrosome, postacrosomal region, mitochondria associated with the middle piece, and so on. Changes in the patterns of lectin binding have been noted during sperm maturation in the epididymis, during capacitation, and after the acrosome reaction, and, in some instances, these studies contribute to the understanding of mechanism that may mediate these transformations. This is particularly true of situations where lectin labeling or binding studies have been used in conjunction with biochemical or other correlative methods to synthesize a more detailed picture of the sperm surface.

Regional differences in distribution of surface proteins over the bull spermatozoa

Surface-radioiodinated bull spermatozoa were ultrasonicated and fractionated by Percoll-gradient centrifugation. The different fractions obtained were solubilized and analyzed by SDS-polyacrylamide gel electrophoresis. Three fractions containing sperm heads, midpieces, and membranes and small fragments of the principal pieces were obtained. The electrophoresis revealed 5 main peaks representing the radioiodinated surface proteins with molecular weights of 80 000-90 000 (Ia), 68 000-75 000 (Ib), 42 000-47 000 (II), 33 000-37 000 (III) and 15 000-18 000 (V) from the intact spermatozoa as well as from each sperm fragment fraction. The major differences between fractions were in the relative magnitudes of the peaks. The peak II characteristically dominated in the head fraction, but was very small in the midpiece fraction. The results from the present study suggest that the peak II seen in the intact spermatozoa is mainly located on the head plasma membrane and that the differences in the sperm surface properties may be due to the uneven distribution or surface exposure of the proteins.