Requirement of sperm-oocyte plasma membrane fusion for establishment of the plasma membrane block to polyspermy in human pronuclear oocytes

We investigated whether the incorporation of the sperm membrane into the oolemma contributes to the human plasma membrane block to polyspermy. We used zona pellucida-free oocytes fertilized by intracytoplasmic sperm injection (ICSI) or activated by parthenogenetic activation. Only two of the 35 pronuclear oocytes fertilized by spermatozoa (control) demonstrated one single penetrating spermatozoa. In contrast, the majority of ICSI and parthenogenetically activated pronuclear oocytes were penetrated with an average of three spermatozoa per oocyte. The number of fused and binding spermatozoa of ICSI and parthenogenetically activated oocytes were significantly higher than in control oocytes (3.5+/-0.6 and 4.3+/-0.6 for ICSI; 3.0+/-0.3 and 3.8+/-0.4 for activated and 0.2+/-0.1 and 0.6+/-0.2 for controls, respectively, P < 0.01). Furthermore, the cortical granules were released from the cortex of ICSI and calcium ionophore-puromycin-activated pronuclear oocytes to the same extent as that of pronuclear oocytes fertilized by spermatozoa. These results suggest that the establishment of the plasma membrane block to sperm penetration in the human oocyte may require a fusion process between sperm and oocyte plasma membranes.

Development of a simple, portable carbon dioxide incubator for in vitro production of bovine embryos

The objective of this study was to develop a simple and portable CO2 incubator using effervescent granules (EG) and to examine the effect of negative and positive air pressure for in vitro maturation (IVM), fertilization (IVF) and culture (IVC) of bovine oocytes. In experiment 1, cumulus-oocyte complexes (COCs) were matured (22 h), fertilized (5 h) and cultured (7 days) using 0.25, 0.5 or 1.0 g of EG per 0.6 l added to maintain an optimum level of CO2 (approximately 3, 6 or 12%, respectively) for in vitro production of embryos. Control oocytes, zygotes and embryos were cultured in a standard CO2 incubator. The blastocyst production rates observed on Days 7 to 9 after insemination were 20.5+/-4.2%, 18.5+/-3.9% and 28.7+/-5.1% for the 0.25 g EG, 0.5 g EG treatments and control, respectively. These rates were significantly higher (P < 0.05) than that of the 1.0 g EG treatment (8.7+/-2.6%). The number of cells in the inner cell mass (ICM) and trophectoderm (TE) produced from blastocysts using the control procedure were 40.8+/-2.9 and 81.2+/-5.3, respectively, and were higher (P < 0.05) compared to the 0.50 g EG (34.6+/-2.9 and 66.8+/-5.7) and 1.0 g EG treatments (33.4+/-3.4 and 67.2+/-7.3). In experiment 2, COCs were placed in a small box with 0.25 g of EG so that the effects on IVM, IVF and IVC of positive or negative air pressure could be compared. The blastocyst production rate observed in the negative air pressure treatment (29.6+/-4.6%) was higher (P < 0.01) than that of the positive air pressure treatment (6.2+/-1.5%) or the normal treatment pressure (P < 0.05; 18.7+/-4.2%) but did not differ from that of the control (30.7+/-4.4%). These results indicate that this simple type of incubator with negative air pressure can be successfully used for in vitro production of bovine embryos and could be used at the field level.

Peritoneal fluid from rabbits or goats as media for in vitro maturation, fertilization and initial culture of caprine oocytes

The efficacy of peritoneal fluid from rabbit and goat for in vitro maturation, fertilization and initial culture of embryos from caprine oocytes was evaluated. Peritoneal fluid was collected from adult female goats (n = 9) or rabbits (n = 9). Good quality oocytes were subjected to in vitro maturation and fertilization in three different media viz. Tissue Culture Medium (TCM-199), goat Peritoneal Fluid (gPF) and rabbit Peritoneal fluid (rPF). Maturation rates were 74.7+/-2.07% and 63.6+/-5.28% in TCM-199, gPF 65.8+/-2.54% and 55.6+/-3.79%, and rPF 57.7+/-1.78% and 44.6+/-3.01% when evaluated on the basis of cumulus cell expansion and the achievement of metaphase-II stage, respectively. However, no significant differences were observed in respect of maturation rate between the control and gPF and between gPF and rPF groups. Freshly ejaculated buck semen was treated with heparin (10 microg/ml) and after 45 min incubation with heparin, 8.0% sperm were live and acrosome reacted. The proportions of fertilized oocytes based on male and female pronuclei formation or on cleavage development were 50.5+/-5.03, 42.3+/-3.15 and 34.2+/-1.98%; 31.0+/-2.80, 27.9+/-2.12 and 21.8+/-1.69% for TCM, gPF and rPF, respectively. It was concluded that peritoneal fluids either from goats or rabbits could be used as an alternative medium to TCM-199. However, further research is required to confirm its efficacy for embryo development up to the blastocyst stage.

Pre-freezing sperm preparation does not impair thawed spermatozoa binding to the zona pellucida

The present study was conducted to assess the fertilizing potential of frozen-thawed spermatozoa, which were cryopreserved after separation on a Percoll gradient, or washed out of seminal plasma. For this purpose, binding to the zona pellucida and other characteristics of the treated sperm cells were compared with those of cryopreserved spermatozoa from the same original sample which were not manipulated before freezing. Semen specimens were obtained from 80 candidates for sperm donation. Percoll-treated sperm samples compared with the sibling, unprocessed controls had significantly higher values of sperm motility characteristics and per cent of cells with normal morphology after freezing and thawing. Sperm binding ability to the zona pellucida was not statistically different (109 +/- 8.1% and 94 +/- 6.7% in unprocessed and Percoll-treated samples respectively). Sperm specimens processed by washing had significantly higher values for motility characteristics than untreated sibling samples, but no differences were found between the treated and untreated samples for morphology and binding to the zona pellucida (hemizona index of 75 +/- 7.0% and 76 +/- 6.7% in unprocessed and washed samples respectively). These findings suggest that, judged by the binding assay, the aforementioned pre-freezing separation processes have no adverse effect upon the fertilizing potential of the thawed sperm cells. These procedures make it possible to optimize the progressive motile sperm cell concentration of the frozen specimen, which facilitates the storage of samples with good quality, even when the features of the original semen are sub-optimal.

[Sperm morphology and xenogenic human sperm-hamster oocyte penetration assay in vitro]

The aim of this study was to evaluate sperm morphology (teratozoospermia) and its effect on xenogenic human sperm-hamster oocyte penetration assay (HOPA). Sperm morphology assessment was performed in 140 infertile patients and 25 healthy individuals. According to Kruger's strict criteria teratozoospermia was diagnosed in 38 individuals out of 140 infertile males. HOPA assay was performed for 20 teratozoospermic patients and 10 healthy volunteers. No significant decrease in HOPA values was observed in cases of isolated teratozoospermia. The sperm anomaly severely influencing HOPA values was asthenozoospermia. We believe that evaluation of sperm morphology according to the strict criteria of Kruger should be applied for routine andrological practice which reflects rapidly changing 'normal' values of human semen.

Use of failed-fertilized oocytes for diagnostic zona binding purposes after sperm binding improvement with a modified medium

PURPOSE

Because the availability of prophase oocytes for zona binding testing is limited, we compared sperm binding to the zona of failed-fertilized intracytoplasmic sperm injection (ICSI) and in vitro fertilization (IVF) oocytes after incubation in a standard IVF medium and a specially composed binding improvement medium.

METHODS

Semen samples from nine patients and nine fertile donors were separated in parallel by the standard swim-up method in both media. Subsequently, hemizona assays were performed with prophase, failed-fertilized ICSI and IVF oocytes.

RESULTS

Sperm separation resulted in a significantly higher sperm count (P < 0.01) and progressive motility (P = 0.018) in binding improvement medium. Moreover, spermatozoa coincubated with hemizonae (prophase, failed-fertilized ICSI and IVF oocytes) in binding improvement medium bound significantly more to hemizonae than in the controls (P < 0.01). However, the hemizona index did not differ.

CONCLUSIONS

Thus, the limited number of human zonae can be increased by the use of oocytes that failed to fertilize during ICSI or IVF. This will lead to a qualitative improvement of the diagnostic spectrum in male-factor infertility.

Mediation of sperm-egg fusion: evidence that mouse egg alpha6beta1 integrin is the receptor for sperm fertilinbeta

BACKGROUND

INTRODUCTION

A key step leading to fertilization is the binding of sperm to the egg plasma membrane. When a mammalian sperm reaches the egg plasma membrane, fertilinbeta, an extracellular sperm membrane protein, is believed to bind to an egg plasma membrane receptor triggering fusion. We set out to identify the fertilinbeta binding partner on the egg plasma membrane.

RESULTS

We synthesized an 125-labeled peptide with the consensus Asp-Glu-Cys-Asp (DECD) sequence of fertilinbeta's disintegrin domain. This peptide contains a benzophenone photoaffinity probe and inhibits sperm-egg fusion. Upon photoactivation in the presence of whole mouse eggs, a single polypeptide was covalently labeled. This polypeptide has been identified by immunoprecipitation as an alpha6 integrin complexed with beta1 integrin.

CONCLUSIONS

Our experiments establish that small peptides containing the consensus DECD sequence of sperm fertilinbeta bind specifically to an alpha6beta1 integrin receptor on the egg membrane. We conclude that fertilinbeta binds directly to the alpha6beta1 integrin on the egg surface and this partnership mediates sperm-egg fusion.

The passage of Ca2+ and fluorescent markers between the sperm and egg after fusion in the mouse

Mouse sperm-egg fusion was examined using two-photon and confocal microscopy. A delay of several minutes occurred between the first observable event of fusion (which was the diffusion of Ca2+-sensitive dyes from egg into sperm) and any change in egg cytoplasmic Ca2+. When indo-1 dextran was used to obtain ratiometric two-photon images, there was no detectable local increase in egg cytoplasmic Ca2+ near the site of sperm fusion. However, the sperm underwent a Ca2+ transient which appeared to be coincident with the egg cytoplasm Ca2+ transient, which suggested that there was a high permeability pathway for Ca2+ between egg and sperm. To exclude this pathway from providing trigger Ca2+ for the egg transient, we reduced bathing [Ca2+] to approx. 18 microM and 13nM (with EGTA). In these conditions the first egg Ca2+ transient was not prevented, which makes an obligatory role for extracellular Ca2+ in the initiation of the egg Ca2+ transient unlikely. Both FITC-albumin (70 kDa) and 10 kDa dextran-linked Ca2+ indicators were able to diffuse into the sperm from the egg. In addition, phycoerythrin (240 kDa) rapidly diffused into the sperm shortly after fusion (but before any changes in Ca2+ occurred). This suggests that the ‘pore(s)’ that form during sperm-egg fusion must be at least 8 nm in diameter. These data are compatible with the idea that a diffusible sperm protein could trigger the observed changes in intracellular Ca2+ in the egg, but do not exclude the possibility that other second messengers are generated during sperm-egg fusion.

Modulation of integrin function inhibits HIV transmission to epithelial cells and fertilization

Integrin-mediated adhesive interactions are viewed in the context of HIV transmission to susceptible cells and fertilization. The ability of a low-molecular-weight non-peptide integrin modulator to inhibit HIV infection (virus-to-cell and cell-to-cell) and sperm-egg fusion is demonstrated. It is concluded that integrin-modulating substances offer significant promise as female-controlled means for preventing sexual transmission of HIV (whatever entity acts as HIV vector in semen and other penile secretions) and as female-controlled contraceptives.

Expanded cumuli induce acrosome reaction in boar sperm

The authors investigated acrosomal changes occurring in boar sperm that interact with the expanded cumulus matrix surrounding ovulated pig oocytes. Samples of washed boar sperm obtained from six donors were incubated for 4 hr under capacitating conditions and exposed either to solubilized zonae pellucidae (ZP) or solubilized expanded pig cumuli (SEC) obtained from IVM oocytes. Alternatively, hyaluronic acid, laminin, or fibronectin, components of the extracellular matrix (ECM) were added to capacitated sperm. Acrosomal integrity was evaluated 1 hr later by using FITC-PSA staining. Solubilized cumuli induced acrosome reaction (AR) in a dose-dependent manner with a saturating effect exerted at 2.5 SEC/50 microl. Both 500 nM fibronectin and 500 nM laminin stimulated acrosomal exocytosis, the latter being more effective and inducing saturating levels of AR. By contrast, hyaluronic acid did not affect acrosomal status. Preincubation with anti-laminin antibodies completely prevented the inducing activity of SEC without affecting the activity of solubilized ZP. Consistent with these data, the integrin VLA-6, a receptor with high affinity for laminin, was detected by immunoblotting on the plasma membrane of capacitated boar spermatozoa. In addition, its immunoneutralization, obtained with the preincubation of capacitated sperm with the antibody raised against the alpha chain of VLA-6 integrin, prevented AR upon exposure to laminin or SEC (10.7+/-3.2 and 10.2+/-1.0% respectively), while the samples retained their responsiveness to ZP (29.6+/-1.2%). The results demonstrate that the interaction between laminin, entrapped in the expanded cumuli, and specific integrins present on the sperm membrane can initiate AR, thus taking part in the process of sperm-egg recognition.

Early events in mammalian egg activation

The fertilizing spermatozoon initiates a series of events in the mammalian egg, referred to as 'egg activation'. These biochemical and morphological events include a transient rise in intracellular Ca2+ concentration ([Ca2+]i) that leads to the cortical reaction (CR) and the establishment of the block to polyspermy on the one hand, and to the resumption of meiosis and later embryonic mitotic divisions on the other. The initial increase in [Ca2+]i appears to be critical for the initiation of egg activation. However, another second messenger, protein kinase C (PKC), was also suggested as a possible inducer of some aspects of egg activation. The review focuses on early events during mammalian sperm-egg interaction and discusses possible roles of Ca2+ and PKC in egg activation.

Sperm-triggered calcium oscillations during meiosis in ascidian oocytes first pause, restart, then stop: correlations with cell cycle kinase activity

We have investigated the relationship between the sperm-triggered Ca2+ oscillations and the activities of two cell cycle kinases (MPF activity and MAP kinase activity) at fertilisation of Ascidiella aspersa oocytes. Maturation Promoting Factor (MPF) activity is elevated in the metaphase I (MI)-arrested unfertilised oocyte (as measured by phosphorylation of exogenous histone H1) and falls 5 minutes after fertilisation to remain at low levels for 5 minutes. The first polar body (pb1) is extruded when the MPF activity is low. The MPF activity is elevated again 15 minutes after fertilisation and finally becomes inactivated 25 minutes after fertilisation when the pb2 is extruded. MAP kinase activity increases from an initially elevated level to reach maximal activity 10 minutes after fertilisation and subsequently falls to reach low levels 25 minutes after fertilisation. Sperm trigger a series of Ca2+ oscillations that pause for 5 minutes while only the MPF activity is low and are present when both MPF and MAP kinase activity are elevated. We next attempted to determine whether the second phase of calcium oscillations is required to reactivate the MPF activity that precedes extrusion of the second polar body. To do this, we triggered a monotonic Ca2+ signal. This leads to the inactivation of MPF followed by MPF reactivation. The MPF activity then remains elevated for an extended period of time. During this period, the chromatin remains condensed and a metaphase II (MII) spindle forms. Fertilisation of these MII oocytes triggers extrusion of pb2 in 7 minutes. Interestingly, the second phase of Ca2+ oscillations is completely absent when MII oocytes are fertilised. Thus, in both MI and MII oocytes, the sperm-triggered Ca2+ oscillations follow the MPF activity. Finally we discuss our finding that the Ca2+ release system remains sensitive during the metaphase-like state (including the period when the Ca2+ oscillations pause).

Mouse oocytes and parthenogenetic eggs lose the ability to be penetrated by spermatozoa after fusion with zygotes

Fertilised mouse eggs develop the oolemma block to sperm penetration within 1 h. This block makes zona-free eggs at the pronuclear stage (zygotes) fully resistant to sperm penetration. In this study we investigated whether this block can spread--as a result of cell fusion--to the oolemma of eggs that are competent to be penetrated by spermatozoa. Preovulatory (GV) oocytes, ovulated oocytes in metaphase II (MII) and 1-cell parthenotes were fused with zygotes and the hybrid cells inseminated at various intervals after fusion. Sperm penetration was assessed on the basis of the presence of Giemsa-positive sperm heads in the air-dried preparations. The oolemma block to sperm penetration develops in all types of hybrids although at different speeds: it develops fast (2-3 h) in oolemma derived from MII oocytes and artificially activated eggs, and slowly in oolemma derived from GV oocytes. In the GV oocyte-zygote hybrids the time of formation of the block varied: while 50% of cells lost the ability to fuse with sperm by 2 h after fusion, in the remaining cells the block must have developed some time between 5 and 18 h after fusion. How these sperm-induced modifications of the oolemma of fertilised egg spread in the hybrid cell and render the 'virgin' part of oolemma resistant to sperm penetration remains unknown.

p-Aminobenzamidine-sensitive acrosomal protease(s) other than acrosin serve the sperm penetration of the egg zona pellucida in mouse

It has been reported that a significant delay in protein dispersal from the acrosomal matrix is observed in wild-type sperm by adding p-aminobenzamidine, a trypsin/acrosin inhibitor, to the incubation medium. The pattern of this delayed release was similar to that of the acrosin-deficient mutant mouse sperm (Yamagata et al., J. Biol. Chem., 273, 10470-4, 1998). In the present study, no further delay in protein dispersal was found when the acrosin-deficient sperm were treated with p-aminobenzamidine, indicating that among the p-aminobenzamidine-sensitive protease(s) only acrosin may function to accelerate this process. Although the acrosin-deficient sperm penetrated the zona pellucida (Baba et al., J. Biol. Chem., 269, 31845-9, 1994), the addition of p-aminobenzamidine to the fertilisation medium caused a significant inhibition of fertilisation in vitro. This indicates that there is a p-aminobenzamidine-sensitive protease(s) other than acrosin participating in the zona penetration step. Indeed, we demonstrated that a non-acrosin protease with a size of 42 kDa was present in the supernatant of the acrosome-reacted sperm suspension. The enzyme was inhibited by p-aminobenzamidine, diisopropyl fluorophosphate and N alpha-tosyl-L-lysine chloromethyl ketone, and was apparently activated by acrosin.

The Parkes Lecture. Heat and the testis

The evidence for the lower temperature of the testes of many mammals is summarized, and the reasons suggested for the descent of the testes into a scrotum are discussed. Descriptions are given of the various techniques used for studying the effects of heat on the testis, whole body heating, local heating of the testes (by inducing cryptorchidism, scrotal insulation or immersion of the scrotum in a water bath), and heating of tissue or cell preparations in vitro. The effects of heat are discussed, effects on the testis (weight, histology, physiology, biochemistry and endocrinology), on the numbers and motility of spermatozoa in rete testis fluid and semen, on fertilizing ability of spermatozoa and on the subsequent development of the embryos produced when spermatozoa from heated testes are used to fertilize normal ova. The possible mechanisms for the damaging effects of heat are discussed, as well as the importance of heat-induced abnormalities in male reproduction in domestic animals and humans.

Immunological characterisation of the acrosomal filament in the marine shrimp Sicyonia ingentis

During sperm/egg interaction, the sperm of Sicyonia ingentis undergoes a unique biphasic acrosome reaction. After acrosomal vesicle exocytosis, the sperm generates an acrosomal filament, over a period of 4-6 min, that is approximately 10 microns in length. Neither actin filaments nor normal microtubules have been demonstrated at the ultrastructural level of this unusual filament. Using a battery of cytoskeleton-directed antibodies the biochemical nature of this filament has been investigated. Antibodies to actin and tubulin do not label the subacrosome or acrosomal filament, but do recognise actin and tubulin in other shrimp tissues. Antibodies to tau, MAP2, and neurofilament medium and heavy subunits were all localised to the subacrosomal region of the sperm. It is interesting, however, that only the two clones of neurofilament monoclonal antibodies recognised the acrosomal filament. Electrophoretic and Western blot analysis in conjunction with amino acid sequencing revealed that the proteins localised to the acrosomal filament are of a unique sequence and may represent a new type of protein of centrosomal origin.

Relationship of subnormal semen parameters and subsequent zona pellucida thinning following in vitro fertilization

Infertility due to male factor has been associated with reduced implantation rates despite normal fertilization. The mechanism responsible for lower pregnancy rates is not known. One cause of failure to achieve pregnancy despite transfer of embryos is impairment of zona pellucida (ZP) thinning, which inhibits the embryo from hatching despite initial cell cleavage. This study was designed to evaluate whether there is an association between the ability of the ZP to thin, as measured by ZP thickness on day of transfer, and subnormal semen parameters. Significant differences in ZP thickness (p < 0.05, Kruskal-Wallis) were noted according to median concentration of sperm, total motile sperm, and motile density in that these values were the highest in the group of embryos with the thinnest zona pellucida and lowest in the group with the thickest zona pellucida. Thus, some factor may be missing from sperm from subnormal specimens that normally assists in zona thinning.

Sperm and oocyte treatments to improve the formation of male and female pronuclei and subsequent development following intracytoplasmic sperm injection into bovine oocytes

This study assessed pronuclear formation, the chromosomal constitution, and the developmental capacity of bovine zygotes formed by intracytoplasmic injection of oocytes with sperm, treated or not with dithiothreitol (DTT). Oocytes were matured in vitro for 22-24 h and then centrifuged so that sperm, prepared by swim-up in the presence or absence of 5 mM DTT, could be injected into the cleared area of the ooplasm. Injected oocytes were activated by treatment with 5 microM ionomycin (5 min) and, after a 3-h interval, with 1.9 mM 6-dimethylaminopurine (DMAP) for 3 h. They were then cocultured with bovine oviductal epithelial cells in M199. Sperm treatment resulted in a significantly higher proportion of male pronucleus formation 16 h after injection (40% vs. 11%; p < 0.0001) and a significantly higher rate of blastocyst development (24% vs. 10%; p < 0.005). Sixty-one percent of blastocysts produced with treated sperm were diploid. Of 12 blastocysts produced with treated sperm and sexed by a polymerase chain reaction, 4 were male and 7 female, and in one a definite diagnosis could not be made. Embryo transfer (2 embryos per heifer) resulted in pregnancies in 6 of 16 recipients at Day 49, but none was carried to term. These results show that the efficiency of bovine intracytoplasmic sperm injection can be improved by sperm pretreatment with DTT and by oocyte activation with ionomycin plus DMAP, although the developmental capacity of the resulting embryos remains limited.

Rat oocytes fertilized in modified rat 1-cell embryo culture medium containing a high sodium chloride concentration and bovine serum albumin maintain developmental ability to the blastocyst stage

A suitable chemically defined culture medium for 1-cell rat embryos (mR1ECM) was modified to obtain sperm penetration, and the developmental competence of oocytes fertilized in the medium was compared to that of oocytes fertilized in a traditional medium, modified Krebs-Ringer bicarbonate medium (mKRB). Sperm penetration was not observed when polyvinyl alcohol was replaced with BSA in mR1ECM (mR1ECM-BSA); the incidence was improved only when the osmolarity in mR1ECM-BSA was increased to that in mKRB (310 mOsm) by addition of NaCl. The proportion of oocytes penetrated in mR1ECM-BSA with NaCl increased (71.6 +/- 6.9%), which was not different compared to that in mKRB (76.7 +/- 13.7%). High incidences of sperm penetration (88.8 +/- 4.1% to 93.1 +/- 5.1%) were also observed when NaCl concentration in mR1ECM-BSA was increased from 76.7 mM to 100-130 mM. The incidence of embryos developing to the morula and blastocyst stages was higher when fertilized in mR1ECM-BSA containing 110-130 mM NaCl (91-94%) than in mKRB (70%). A total of 5 offspring were obtained after transfer of the morulae and blastocysts (69 embryos/7 females). These results demonstrate that a high developmental ability of rat embryos to the blastocyst stage is attained when the embryos have been fertilized in mR1ECM-BSA containing 110-130 mM NaCl and then cultured in mR1ECM.

High-resolution mapping of sperm function defects in the t complex fourth inversion

Structural variants of the mouse Chr 17-specific t complex, known as t haplotypes, express factors that alter the ability of sperm to carry out their roles in the normal fertilization process. In previous studies of males carrying heterospecific combinations of the t complex, we discovered a unique M. spretus/t haplotype phenotype of male sterility. In additional studies with mice carrying a series of M. spretus-M. m. domesticus recombinant Chr 17 homologs and a complete t haplotype (S-+/t), we monitored physiological aspects of sperm function to map a locus (Hst6) responsible for expression of the t-specific "curlicue" sperm flagellar curvature phenotype to 1 cM within the fourth inversion of the t complex. In the present report, we quantitatively analyze the in vitro capability of sperm from mice with similar S-+/t Chr 17 genotypes to fertilize zona pellucida-free mouse eggs. The results identify a locus, Stop1, mapping distal to Pim1, with acute effects on the ability of sperm to penetrate the oolemma. The data suggest that Stop1 is a complex locus consisting of at least two genetic elements, a proximal one overlapping the Hst6 locus, and another, distal to the Hst6 locus. Further quantitative analyses of the "curlicue" phenotype produced by sperm derived from these same animals indicate that expression of this chronic flagellar curvature phenotype also derives from at least two elements, both mapping within the Hst6 locus. Thus, these studies provide higher resolution mapping of the molecular basis of t haplotype-specific sperm dysfunction emanating from In(17)4.

Voltage-dependent activation of frog eggs by a sperm surface disintegrin peptide

Fertilin, a sperm protein of the metalloprotease/disintegrin/cysteine-rich (MDC) family, plays a critical role in sperm-egg binding in mammals. Peptides corresponding to the disintegrin domain of fertilin and antibodies against fertilin have been shown to inhibit mammalian sperm-egg binding and fusion. A protein from the same family, xMDC16, was recently cloned from frog (Xenopus laevis) testis and was found to be involved in frog sperm-egg binding. Here we report that xMDC16 is localized predominantly on the posterior surface of egg jelly-activated sperm, and peptides from the disintegrin domain of this protein activate eggs when applied near the egg surface. Egg activation was dependent on (1) specific amino acid residues (KTX); (2) the presence of divalent cations, but not external Ca2+ alone; and (3) voltage across the egg plasma membrane. This is the first demonstration of egg activation in vertebrates by the surface application of a peptide derived from a sperm surface protein, supporting a model for egg activation that involves a signal transducing receptor for sperm in the egg's plasma membrane.