Showing papers on "Sperm published in 1975"
TL;DR: Initiation, but not completion, of removal or alteration of sperm surface seminal plasma antigenic components was a necessary prerequisite to in vitro insemination for successful achievement of fertilization in vitro.
Abstract: This research was carried out to define in vitro conditions that would enable ejaculated rabbit sperm to fertilize ova in vitro. During 20 mm exposure of sperm cells to defined media of increasing NaCI concentrations, progressive removal or alteration of sperm surface seminal plasma antigenic components was initiated and completed as reflected by an immunological assay at approximately 300 and 380 mOsm/kg, respectively. Hypertonic (380 mOsm/kg) medium effected complete removal or alteration of these components as determined by the immunological assay during the first 5 mm of sperm treatment. Isotonic (305 mOsm/kg) treatment was shown to have effected removal or alteration of some but not all of the antigenic sperm coating seminal plasma components detectable by this means during 20 mm of exposure. Sperm within the perivitelline apace, presence of pronuclei. and 2- and 4-cell cleavage stages were taken as evidence for fertilization. None of 34 ova incubated for 27 h in vitro with once-washed sperm showed evidence of fertilization. Following treatment of sperm with hypertonic (380 mOsm/kg) medium prior to in vitro insemination, proportions of ova showing evidence of fertilization ranged from 8.1 percent (12 to 148 ova) to 72.2 percent (52 of 72 ova); and, following treatment of sperm with isotonic (305 mOsm/kg) medium, fertilization of ova ranged from 0 percent (0 to 19 ova) to 73.9 percent (SI of 69 ova) when results were considered according to individual male sperm donors. No large differences were found by the immunological assay that could be linked to variability of fertilizing ability of sperm from different bucks. Differences in metabolic characteristics of sperm cells was suggested as a likely reason for differences in fertilizing ability of sperm from different bucks. In experiments using sperm and ova from the same sources, no differences in fertilization results were apparent following 305 and 380 mOsm/kg sperm treatments, Initiation, but not completion, of removal or alteration of sperm surface seminal plasma antigenic components, then, was a necessary prerequisite to in vitro insemination for successful achievement of fertilization in vitro. Sperm penetration into ova occurred in some cases before 7-10 h after insemination (4 of 54 ova penetrated), but actively motile sperm were found within the perivitelline apace of other ova as late as 25 h after insemination. One hundred and seventy-six 2- and 4-cell stage embryos were transferred to 14 recipient does. Twenty-four embryos (13.1 percent) implanted in 6 recipients but most were resorbed. Three embryos resulting from in vitro fertilization with in vitro capacitated ejaculated rabbit sperm were carried successfully to term by 2 recipients and 2 of the offspring were males. This provides documentation for the authenticity of in vitro capacitation of ejaculated sperm of a mammalian species and represents the initial successful combination of in vitro sperm capacitation with in vitro fertilization and embryo transfer in the rabbit.
1,133 citations
TL;DR: The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.
Abstract: The sperm of (C57BL X C3H)F1 mice were examined 1, 4, and 10 weeks after a subacute treatment with one of 25 chemicals at two or more dose levels. The fraction of sperm that were abnormal in shape was elevated above control values of 1.2-3.4% for methyl methanesulfonate, ethyl methanesulfonate, griseofulvin, benzo[a]pyrene, METEPA [tris(2-methyl-l-aziridinyl)phosphine oxide], THIO-TEPA [tris(l-aziridinyl)phosphine sulfide], mitomycin C, myleran, vinblastine sulphate, hydroxyurea, 3-methylcholanthrene, colchicine, actinomycin D, imuran, cyclophosphamide, 5-iododeoxyuridine, dichlorvos, aminopterin, and trimethylphosphate. Dimethylnitrosamine, urethane, DDT [1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane], 1,1-dimethylhydrazine, caffeine, and calcium cyclamate did not induce elevated levels of sperm abnormalities. The results suggest that sperm abnormalities might provide a rapid inexpensive mammalian screen for agents that lead to errors in the differentiation of spermatogenic stem cells in vivo and thus indicate agents which might prove to be mutagenic, teratogenic, or carcinogenic.
836 citations
01 Jan 1975
TL;DR: A tentative hypothesis is proposed that after hypophysectomy and castration the almost immediate regression of the endoplasmic reticulum inhibits the secretory process and blocks sperm maturation.
Abstract: A review of endocrine control of the development and maintenance of sperm fertilizing ability in the epididymis is presented. Functional changes in epididymal spermatozoa androgen regulation of the epididymis and mechanism of the androgen regulation of sperm maturation and survival are the 3 main topics of discussion. The following tentative hypothesis is proposed: 1) products originating from the epididymal cells under androgen stimulation are secreted into the epididymal lumen where they affect sperm maturation and survival through a yet unknown mechanism and 2) after hypophysectomy and castration the almost immediate regression of the endoplasmic reticulum inhibits the secretory process and blocks sperm maturation.
335 citations
TL;DR: Sermatozoa from two brothers who are not twins were found to be straight and immotile and the simplest explanation for the simultaneous lack of arms and sperm motility appears to be that the two brothers have a genetic disorder involving production, assembly, or attachment of the dynein arms.
Abstract: Sermatozoa from two brothers who are not twins were found to be straight and immotile. Examinations of the sperm showed that oxygen consumption and lactic acid production were normal; viability tests showed that the percentage of dead sperm was not increased. The ultrastructural appearance of the sperm tail was normal except for a complete lack of dynein arms and some irregularities in the arrangement of the accessory fibers and the longitudinal columns of the fibrous sheath. The mitochondrial apparatus and the sperm head conform to the conventional model. According to the sliding-filament hypothesis first proposed by Afzelius (1959. J. Biophys. Biochem. Cytol. 5:269.), the arms are responsible for the bending movements of the tail. The simplest explanation for the simultaneous lack of arms and sperm motility appears to be that the two brothers have a genetic disorder involving production, assembly, or attachment of the dynein arms.
282 citations
TL;DR: Results suggest that phosphorylation of sperm histone is involved in the process of chromatin condensation during transformation of spermatozoa in the epididymis.
181 citations
TL;DR: It appears that the Mn-2+-sensitive adenylate cyclase is initially present in the cytoplasm either unattached or loosely bound to intracellular membranes and becomes firmly attached to sperm membranes later in development.
Abstract: A distinctive Mn-2+-sensitive adenylate cyclase [ATP pyrophosphate-lyase(cyclizing), EC 4.6.1.1] system insensitive to fluoride has been found in rat seminiferous tubules and epididymal sperm. The development of this distinctive adenylate cyclase in testis was studied during spermatogenesis. It was first detectable in seminiferous tubules in immature rats at about the time of the first reductive divisions and the appearance of spermatid cells. The specific activity of the enzyme increased substantially during the period of spermatogenesis when spermatids develop into mature spermatozoa, and reached maximal values in the testis of adult rats. After centrifugation of testis tissue homogenates at 105,000 X g for 60 min, the Mn-2+-sensitive adenylate cyclase activity was found in the cytosol. The enzyme remains in solution after centrifugation at 300,000 X g for 5 hr or at 180,000 X g for 24 hr and passes through a 0.22 mum Millipore filter. Electron microscopic examination showed no visible membrane fragments or vesicles in the filtered supernatant. The Mn-2+-sensitive adenylate cyclase system is also present in epidiymal sperm. However, in the sperm obtained from either the caput or the cauda of epididymis, the adenylate cyclase is membrane-associated and found in particulate fractions of sperm homogenates. It therefore appears that the Mn-2+-sensitive adenylate cyclase is initially present in the cytoplasm either unattached or loosely bound to intracellular membranes and becomes firmly attached to sperm membranes later in development. This occurs either during the process of maturation of spermatids into sperm or during the transport of the testicular sperm into the epididymis.
176 citations
TL;DR: A 300 fold range of epididymal sperm concentrations has been tested to determine whether there is a relationship between sperm concentration and level of fertilization achieved in vitro of mouse eggs and consistently high results were obtained.
Abstract: A 300 fold range of epididymal sperm concentrations (0.3-90 X 105/ml) has been tested to determine whether there is a relationship between sperm concentration and level of fertilization achieved in vitro of mouse eggs. While very low concentrations (0.3-1.25 X 105/ml) resulted in relatively low fertilization (43-64 percent), those in the range of 2.5-90 X 105/ml gave fertilization rates of 80- 94 percent. Consistently high results were obtained with sperm counts
175 citations
TL;DR: A positive relationship was found between sperm density and percentage of motile sperm; the relationship between motility and the logarithm of sperm density was represented by a straight line; the slope of the line was highly significant, although the correlation coefficient was weak.
165 citations
TL;DR: Bull sperm that had been extracted with 0.2% Triton X-100 could be reactivated with ATP, and their movement closely resembled the motion of intact live sperm, and the presence of an active sliding mechanism of filament interaction in bull spermatozoa was demonstrated.
Abstract: Bull sperm that had been extracted with 0.2% Triton X-100 could be reactivated with ATP, and their movement closely resembled the motion of intact live sperm. Their motility required the presence of ATP, magnesium, and a medium of suitable salt concentration and pH. When Triton-extracted bull sperm were digested briefly with trypsin at pH 9.0, they appeared to retain most of their normal structure, but subsequent exposure of the digested sperm to ATP caused a disintegration of the flagellar structure. Direct observation of this disintegration by light microscopy, using dark-field illumination, combined with an electron microscope study of preparations of the disintegrated sperm, demonstrated the presence of an active sliding mechanism of filament interaction in bull spermatozoa. Human sperm subjected to the same procedures showed similar patterns of reactivation and of
144 citations
126 citations
TL;DR: It was concluded that receptors were masked by constituents in epididymal and seminal fluid, and Shedding of the surface coat may be evidence for membrane alterations during capacitation which prepare sperm for fertilization.
TL;DR: Although sperm entry occurred throughout the animal region, most penetration paths started within 60° of the animal pole, and this movement appeared to be due to a contraction of the cortex towards the animal Pole that occurred 3–4 min after activation of the egg.
TL;DR: The semen frozen according to the best conditions had a fertilizing ability similar to that of "fresh" semen when the proportion of motile spermatozoa before, and after 1 or 3 hr of incubation was equal to or above 45, 40 and 30% respectively.
Abstract: The influence oftemperature, addition of glycerol, initial freezing temperature, method of dilution, level of glycerol in the diluted semen, equilibration time and type of diluent on the survival and fertilizing capacity of deep-frozen according to the best conditions was compared with that of "fresh" semen. The addition of glycerol at plus30 degrees C resulted in a highly significant decrease in the mean proportion of motile spermatozoa immediately after thawing compared with the effect of addition at plus 4 degrees C. The immersion of the straws at minus55 degrees C significantly reduced the revival of the spermatozoa compared with initial freezing at lower temperatures. The exposure time to glycerol had no significant effect on the survival of spermatozoa after thawing and incubation, but fertility was significantly higher with 4% than with 2% glycerol. The I. N. R. A. diluent provided better sperm survival and a significantly higher conception rate than did lactose-egg yolk extender. The semen frozen according to the best conditions (about 50% of the samples) had a fertilizing ability similar to that of "fresh" semen when the proportion of motile spermatozoa before, and after 1 or 3 hr of incubation was equal to or above 45, 40 and 30% respectively.
TL;DR: A cinemicrographic analysis of fertilization reveals that fusion of sperm and egg occurs between non-motile gametes, indicating that the flagellar motion of sperm is not required.
Abstract: Current research on the mechanisms of sperm-egg fusion, the block to polyspermy, and metabolic activation are described. A cinemicrographic analysis of fertilization reveals that fusion of sperm and egg occurs between non-motile gametes, indicating that the flagellar motion of sperm is not required. The block to polyspermy is reviewed, emphasizing recent work on the role of cortical granule protease in altering sperm receptors of the vitelline layer.
Metabolic activation or derepression at fertilization is highly regulated and occurs in a definite sequence. The primary event appears to be release of intracellular Ca2+. The timing of metabolic derepression is different in starfish oocytes. Here, a part of the derepression occurs during maturation and another part at fertilization.
TL;DR: It is demonstrated here that oestrogen and testosterone affect one aspect of sperm maturation in mice by altering the rate of epididymal sperm transport, and also affect fertility.
Abstract: THE maturation of spermatozoa during passage through the mammalian epididymis, involves changes in motility, metabolism, morphology, biochemical properties and the development of the ability to fertilise ova1. This maturation process, and the maintenance of fertilising ability, is dependent on androgen2. When testosterone levels are lowered by castration or hypophysectomy, sperm from the cauda epididymis have immature acrosomes (guinea pig)3 and lowered fertilising ability (rat)4. These effects are prevented by testosterone treatment. Since reduction of testosterone levels enhances the rate of epididymal sperm transport4,5, the incomplete maturation could result from spermatozoa spending insufficient time in critical regions of the epididymis, as well as from a decreased ability of the epididymis to promote sperm maturation. We demonstrate here that oestrogen and testosterone affect one aspect of sperm maturation in mice by altering the rate of epididymal sperm transport, and also affect fertility.
TL;DR: Progress has been made in defining cell surface components specified by the T/t locus in the mouse, both in their expression on sperm and, in the one case studied, on normal embryonic cells and teratocarcinoma.
Abstract: Progress has been made in defining cell surface components specified by the T/t locus in the mouse, both in their expression on sperm and, in the one case studied, on normal embryonic cells and teratocarcinoma. Some striking analogies between this putative embryonic cell recognition system and the adult major histocompatibility complex are presented.
TL;DR: It is probable that mechanisms have evolved to maintain a low immunogenicity of spermatozoa, and that antibody to a tissue-specific sperm antigen occurs naturally without deliberate immunisation and is readily elicited in a variety of species.
Abstract: ALTHOUGH spermatozoa bear histocompatibility antigens (H-2 in mice1,2 and HL-A in man3,4) accelerated (immune) skin graft rejection is not known to occur in females previously multiply inseminated by a graft donor. The absence of detectable transplantation immunity in inseminated females correlates with the generally low immunogenicity of spermatozoa given by other routes. The decreased antigenicity of spermatozoa is not explained by a privileged immune status of the female reproductive tract as the vaginal route is adequate for immunisation against a variety of antigens5, especially if the tract is wounded6, and antibodies to spermatozoa decrease fertility in some situations7. Thus, it is probable that mechanisms have evolved to maintain a low immunogenicity of spermatozoa. What seems to be an exception to the low immunogenicity of spermatozoa—that antibody to a tissue-specific sperm antigen occurs naturally without deliberate immunisation8,9 and is readily elicited in a variety of species10—may represent a protective mechanism. Many substances present in seminal plasma may exert a suppressive effect by coating sperm membrane antigens or inducing immunosuppression by other means.
TL;DR: In this paper, it was shown that both H-2 and F9 have identical molecular weights and subunit structure, including the presence of a B2-microglobulin-like subunit.
Abstract: Molecules specified by the H-2-linked T/t locus in the mouse are expressed on H-2-negative cells such as early embryos, sperm, and teratoma cells. By means of enzymatic radioiodination of cells and immunoprecipitation of lysates with congenic antiserum, one of these molecules, known as F9, has been obtained from sperm and teratoma cells and compared to H-2 isolated from murine splenocytes. Our studies indicate that both H-2 and F9 have identical molecular weights and subunit structure, including the presence of a B2-microglobulin-like subunit. These findings, taken together with previous studies of TL alloantigens, suggest that a number of gene products of the 9th linkage group show structural homology with each other and, in addition, with immunoglobulin. The genes in question may therefore have arisen from a primitive gene concerned with cellular recognition.
TL;DR: The gametes of four echinoids were combined in four homologous and elevent heterologous crosses in which cross-fertilization did not occur, supporting the previous suggestion thatCross-fertility is prevented by failure ofheterologous sperm to undergo primary gamete binding to the vitelline envelope of ova.
TL;DR: Sperm proacrosin “autoactivation” appeared to be a second order autocatalytic process in which the product of the activation accelerated its own formation, suggesting strongly that rabbit epididymal sperm and rabbit testis proACrosin are identical proteins.
Abstract: Proacrosin, the zymogen form of acrosin was extractedwith 0.25N H2SO4 from unwashed rabbit cauda epididymal spermatozoa. Sephadex G-75 column chromatography of the extract resolved two peaks of epididymal sperm proacrosin, both of which contained low amounts of acrosin prior to activation (a total of 5 percent of the final acrosin activity obtained from complete activation of proacrosin), and were free of trypsin inhibitor. The peak eluted first (peak I) represented 85 percent of the total proacrosin and had an apparent molecular weight (MW) of 73,000 as determined by Sephadex G-100 column chromatography. Complete “autoactivation” of sperm proacrosin peak I resulted in the production of an acrosin with a MW of 38,000. Proacrosin was alsofound in washed epididymalsperm uncontaminated by free cytoplasmic droplets or epididymal fluid. Sperm proacrosin “autoactivation” appeared to be a second order autocatalytic process in which the product of the activation accelerated its own formation. The “autoactivation” was stimulated by Ca�� and inhibited by � These properties of sperm proacrosin agree with our previous data from studies of rabbit testis proacrosin. Also the acrosin obtained by “autoactivating” the sperm and testis proacrosins, had similar apparent Km values for BANA (7.8-10.5 X 10-5M), BAEE (2.1-4.3 X 105M) and TAME (2.4-3.3 X 10-SM), similar pH optima (pH 8.2-8.4), and were similarly inhibited by several trypsininhibitors. These resultssuggeststrongly that rabbit epididymal sperm and rabbit testis proacrosin are identical proteins. Conversion of sperm proacrosin to acrosin (involving the hydrolysis of at least one peptide bond)would appeartobe necessaryifacrosinplaysaroleinfertilization.
TL;DR: The semen zinc levels were determined in 18 volunteers, 132 patients postvasectomy, and in 19 patients with prostatitis with a trend toward increasing zinc concentrations in the groups with increasing fertility potential.
TL;DR: Evidence of sperm chemotaxis to egg water and egg extracts of Ciona intestinalis, a primitive chordate, implies that spermChemotaxis either has evolved independently in groups widely separate on the phylogenetic scale or is widespread in the animal kingdom.
Abstract: CHEMOTAXIS of animal sperm, long thought not to occur1–4, was first proved in the marine coelenterate Campanularia5 and since then has been observed in other hydroids6,8. The species-specificities and cross reactions between sperm and reproductive structures of these species and genera have been described6, and some of the attractants have been isolated and their chemical properties reported7. In spite of circumstantial evidence for sperm chemotaxis in other phyla13,14 the sperm behaviour leading to aggregation has not been described. I now report evidence of sperm chemotaxis to egg water and egg extracts (see Table 1 for details) of Ciona intestinalis (Protochordata: Urochordata), a primitive chordate. These results imply that sperm chemotaxis either has evolved independently in groups widely separate on the phylogenetic scale or is widespread in the animal kingdom.
TL;DR: Observations on an unexpected reduction in the proportion of motile spermatozoa in the isthmus of the rabbit oviduct over the 12-h interval between mating and fertilisation.
Abstract: SPERM transport through the female reproductive tract has been studied extensively in mammals1,2, but no systematic evaluation of the motility of spermatozoa at different levels of the tract after coitus has been reported. We describe a procedure for collecting oviducal spermatozoa and present observations on an unexpected reduction in the proportion of motile spermatozoa in the isthmus of the rabbit oviduct over the 12-h interval between mating and fertilisation.
TL;DR: When 5-thio-D-glucose was fed to male mice at daily dose levels greater than 30 mg/kg sperm development was completely inhibited within 3 weeks and remained so without impairment of libido for the experimental period of 7 weeks, removal from the diet resulted in a resumption of sperm development and fertility within 5 to 8 weeks.
Abstract: When 5-thio-D-glucose was fed to male mice at daily dose levels greater than 30 mg/kg sperm development was completely inhibited within 3 weeks and remained so without impairment of libido for the experimental period of 7 weeks. Removal of this substance from the diet resulted in a resumption of sperm development and fertility within 5 to 8 weeks. Normal litters were sired by males which had recovered after this treatment.
TL;DR: Mouse sperm were labeled in vivo with [3H]arginine and a new fraction (proposed name: musculine) was shown to be the only fraction that was labeled, which represents the end product of a histone transition in mice.
Abstract: Mouse sperm were labeled in vivo with [3H]arginine. The sperm were then followed autoradiographically from the time of label incorporation until after fertilization. The label was completely lost from the sperm head after fertilization, during the oocyte's second meiotic division. That the [3H]arginine was incorporated into a sperm-specific basic protein was demonstrated by fractionating acid extracts of epididymal and ejaculated sperm with polyacrylamide gel electrophoresis. All the histone fractions were resolved in the epididymal extracts, but in addition a band was present that migrated faster than histone F2al and slower than the salmon protamine used as a marker. This new fraction (proposed name: musculine) was also present in ejaculated sperm; it was shown to be the only fraction that was labeled. Musculine therefore represents the end product of a histone transition in mice. It is, however, according to our electrophoretic characterization, not identical to the classical fish protamines. Rather, musculine resembles bovine sperm nuclear protein. Since the loss of this fraction from the sperm head was coincident with the rearrangement of the male genome, before its resumption of transcription, it is suggested that musculine is involved in the control of chromatin that accompanies spermiogenesis and fertilization.
TL;DR: Antibody produced in rabbits against hamster ovary blocked fertilization of golden hamster eggs in vitro by binding to the surface of the zona pellucida and rendering it impenetrable to spermatozoa.
Abstract: Antibody produced in rabbits against hamster ovary blocked fertilization of golden hamster eggs in vitro by binding to the surface of the zona pellucida and rendering it impenetrable to spermatozoa. The antibody was also effective in blocking fertilization in vivo. An intraperitoneal injection of the antibody into females resulted in the complete inhibition of fertilization for approximately 12 days, i.e. three oestrous cycles. This temporary sterility was apparently due to the binding of the antibody to the zona pellucida of oviducal and ovarian oocytes, and dot due to a failure of sperm ascent or capacitation in the female genital tract. Neither the oestrous cycle nor ovulation was affected by the antibody injection.
TL;DR: A review is given on sperm migration to and sperm survival within the human Fallopian tube and the morphology of spermatozoa reaching the ampulla of the oviduct is mostly normal, which seems to be based on the correlation between normal morphology and good motility.
Abstract: A review is given on sperm migration to and sperm survival within the human Fallopian tube. Sperm migration from the external os can be very fast. The survival time of spermatozoa in the oviduct has been demonstrated to be 85 h. Spermatozoa normally enter the abdominal cavity through the open fimbriated end. Laterally closed oviducts retain spermatozoa resulting in a larger number of spermatozoa than in the normal oviduct, where the number of sperm at the site of fertilization is very low. The morphology of spermatozoa reaching the ampulla of the oviduct is mostly normal, which seems to be based on the correlation between normal morphology and good motility. Spermatozoa within the abdominal cavity do not cause antibody formation of any importance for the fertility of the woman.
TL;DR: The Sertoli cells phagocytize residual bodies cast off by developing spermatids and form an association with mature sperm, which resembles that observed in mammals, before the sperm are released into the vasa efferentia as a spermatozeugmata.
Abstract: The structure of the testis of Poecilia latipinna is described with particular reference to Sertoli cell-germ cell relationships during development and maturation of the germinal cyst. The cyst develops when primary spermatocytes become surrounded by a single layer of Sertoli cells at the testis periphery. As spermatogenesis and then spermiogenesis proceed, the cyst moves centrally in the testis toward the ducts comprising the vasa efferentia. In addition to being a structural part of the germinal cyst, the Sertoli cells phagocytize residual bodies cast off by developing spermatids and form an association with mature bodies cast off by developing spermatids and form an association with mature sperm, which resembles that observed in mammals, before the sperm are released into the vasa efferentia as a spermatozeugmata. The results of this investigation are discussed in view of what is known concerning testis structure in other teleosts and similarities between cell functions in teleosts and mammals. It is concluded that teleost Sertoli cells, teleost lobule boundary cells and mammalian Sertoli cells are homologous.
TL;DR: An investigation of the sperm binding characteristics of the mouse zona pellucida found a dramatic difference in the binding of capacitated sperm to zonae of unfertilized eggs and to in vivo produced 2-cell embryos.
Abstract: Experimental conditions were established for an investigation of the sperm binding characteristics of the mouse zona pellucida. Fresh epididymal sperm binding to zonae of unfertilized eggs was a time-dependent process, reflecting the occurrence of sperm capacitation under in vitro incubation conditions. In contrast, capacitated sperm binding in large numbers to zonae of unfertilized ova occurred independently of temporal considerations. A dramatic difference was apparent in the binding of capacitated sperm to zonae of unfertilized eggs (>100 per zona) and to in vivo produced 2-cell embryos (0-5 per zona), providing a basis for assessing the occurrence of a zona reaction. Under comparable conditions, capacitated sperm bound in large numbers to zonae of in vitro produced 2-cell embryos. Possible reasons for a subnormal or inadequate zona reaction in eggs inseminated in vitro have been discussed.
TL;DR: An ultrastructural analysis of polyspermic human ova, obtained by insemination in vitro of zona pellucida-free oocytes, has demonstrated the following: 1. Sperm flagellum entry into the ooplasm is accomplished by sliding, while the sperm plasma membrane is being incorporated into the vitelline membrane as discussed by the authors.