A molecular approach to fertilization. 3. Development of a bioassay for sperm capacitation

ANT1 overexpression models: Some similarities with facioscapulohumeral muscular dystrophy

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant disorder characterized by progressive muscle weakness. Adenine nucleotide translocator 1 (ANT1), the only 4q35 gene involved in mitochondrial function, is strongly expressed in FSHD skeletal muscle biopsies. However, its role in FSHD is unclear. In this study, we evaluated ANT1 overexpression effects in primary myoblasts from healthy controls and during Xenopus laevis organogenesis. We also compared ANT1 overexpression effects with the phenotype of FSHD muscle cells and biopsies. Here, we report that the ANT1 overexpression-induced phenotype presents some similarities with FSHD muscle cells and biopsies. ANT1-overexpressing muscle cells showed disorganized morphology, altered cytoskeletal arrangement, enhanced mitochondrial respiration/glycolysis, ROS production, oxidative stress, mitochondrial fragmentation and ultrastructure alteration, as observed in FSHD muscle cells. ANT1 overexpression in Xenopus laevis embryos affected skeletal muscle development, impaired skeletal muscle, altered mitochondrial ultrastructure and led to oxidative stress as observed in FSHD muscle biopsies. Moreover, ANT1 overexpression in X. laevis embryos affected heart structure and mitochondrial ultrastructure leading to cardiac arrhythmia, as described in some patients with FSHD. Overall our data suggest that ANT1 could contribute to mitochondria dysfunction and oxidative stress in FSHD muscle cells by modifying their bioenergetic profile associated with ROS production. Such interplay between energy metabolism and ROS production in FSHD will be of significant interest for future prospects.

Sperm collection and storage for the sustainable management of amphibian biodiversity

Current rates of biodiversity loss pose an unprecedented challenge to the conservation community, particularly with amphibians and freshwater fish as the most threatened vertebrates. An increasing number of environmental challenges, including habitat loss, pathogens, and global warming, demand a global response toward the sustainable management of ecosystems and their biodiversity. Conservation Breeding Programs (CBPs) are needed for the sustainable management of amphibian species threatened with extinction. CBPs support species survival while increasing public awareness and political influence. Current CBPs only cater for 10% of the almost 500 amphibian species in need. However, the use of sperm storage to increase efficiency and reliability, along with an increased number of CBPs, offer the potential to significantly reduce species loss. The establishment and refinement of techniques over the last two decades, for the collection and storage of amphibian spermatozoa, gives confidence for their use in CBPs and other biotechnical applications. Cryopreserved spermatozoa has produced breeding pairs of frogs and salamanders and the stage is set for Lifecycle Proof of Concept Programs that use cryopreserved sperm in CBPs along with repopulation, supplementation, and translocation programs. The application of cryopreserved sperm in CBPs, is complimentary to but separate from archival gene banking and general cell and tissue storage. However, where appropriate amphibian sperm banking should be integrated into other global biobanking projects, especially those for fish, and those that include the use of cryopreserved material for genomics and other research. Research over a broader range of amphibian species, and more uniformity in experimental methodology, is needed to inform both theory and application. Genomics is revolutionising our understanding of biological processes and increasingly guiding species conservation through the identification of evolutionary significant units as the conservation focus, and through revealing the intimate relationship between evolutionary history and sperm physiology that ultimately affects the amenability of sperm to refrigerated or frozen storage. In the present review we provide a nascent phylogenetic framework for integration with other research lines to further the potential of amphibian sperm banking.

Swimming of Xenopus laevis sperm exhibits multiple gears and its duration is extended by egg jelly constituents

The motility of Xenopus sperm is initiated by the osmotic shock experienced when these cells are ejaculated into low-salinity pond water. Motility is brief and is required for the sperm to penetrate the jelly layers and fertilize the egg. In this study we demonstrate that extracts of egg jelly contain factors that extend the period of sperm motility as well as providing a chemoattractant activity as previously reported. Both activities are partially dependent on extracellular calcium. Time-lapse and video microscopy show that after activation of motility the number of motile sperm decreases rapidly, with a half-time of about 2 min. Addition of 10% v/v egg jelly extract ("egg water") increased the number of motile sperm 2-fold over controls at 20 s and about 4- to 10-fold over controls at 10 min after initiation of motility. Extension of motility lifetime was not mediated by a nonspecific protein or by allurin, the egg-water protein that has chemoattractant activity. The helical path of Xenopus sperm exhibited tight coupling between rotational and forward velocities in egg jelly, but coupling changed rapidly from moment to moment in low-salinity buffer. Our observations suggest that jelly-derived factors regulate both the longevity and directionality of sperm propulsion.

Sperm morphology, motility and fertilisation capacity in the myobatrachid frog Crinia georgiana

Sperm traits have been found to vary between individuals within populations in a variety of taxa. Sperm motility, morphometry and viability may be expected to have important effects on male fertility, although previous studies have found varying patterns, especially in external fertilisers. In the present study, we examined the effects of sperm swimming velocity, the proportion of motile spermatozoa, sperm head and tail length and the proportion of live spermatozoa on fertilisation success in the externally fertilising myobatrachid frog Crinia georgiana using IVF techniques and by controlling sperm numbers. We found no effect of any of the sperm traits we measured on IVF success. Neither did we find any relationship between sperm morphology and sperm performance. There was a negative relationship between sperm viability and male body size, which could be a function of age or an alternative tactic of differential investment in spermatozoa by smaller-sized males using sneak tactics in multiple matings. In contrast with most externally fertilising aquatic organisms, high rates of fertilisation appear to be achieved in C. georgiana with relatively low sperm swimming speeds.

Optimisation of handling, activation and assessment procedures for Bufo marinus spermatozoa

In the present study, we investigated handling, activation and assessment procedures for cane toad (Bufo marinus) spermatozoa. Optimisation of these techniques will facilitate the maintenance of sperm viability during cryopreservation and during in vitro fertilisation (IVF) techniques in reproduction technologies for endangered species. Spermatozoa were taken from testicular macerates and assessed using plasma membrane integrity assays (live/dead stains) and quantitative scores of motility parameters. In the assessment of sperm viability using live/dead stains, there were small but significant differences in the percentage of sperm from cryopreserved samples staining positive with propidium iodide, Hoechst H33258 and Trypan blue; these differences were not large and all stains performed acceptably. Spermatozoa were activated by dilution of testicular macerates in water at one of two dilution ratios (1 : 6 or 1 : 20) with or without 0.1–5.0 mm theophylline. Sperm plasma membrane integrity (unstained spermatozoa) was unaffected by either dilution ratio (osmolarity) or theophylline concentration. However, sperm motility was significantly affected by osmolarity and theophylline concentration. The stimulation of sperm motility increased with higher theophylline concentrations and these strongly interacted with lower osmolarities through a higher dilution ratio of sperm macerates with water. Spermatozoa were exposed to increasing centrifugation forces to determine tolerance to physical stresses encountered during washing procedures. Forces between 50 and 800g were associated with a significant reduction in motility (mean 56 ± 3% decreasing to 27 ± 3%), but did not affect staining. In conclusion, centrifugation should be minimised in anuran sperm washing procedures; osmotic shock associated with higher dilution ratios reduces the capacity of anuran sperm to achieve high percentages of motile sperm, leading to a likely trade-off between dilution required for activation and sperm motility to optimise IVF fertilisation rates; and optimal conditions for sperm motility after activation occur at lower dilutions of suspensions with 5.0 mm theophylline. The present study has improved protocols for the handling of anuran sperm during pre- and post-cryopreservation procedures.

Profiling the morphological distribution of O-linked oligosaccharides

The morphological distribution of oligosaccharides is determined in the egg jelly surrounding Xenopus laevis eggs. This biological system is used to illustrate a method for readily identifying and quantifying oligosaccharides in specific tissues. The extracellular matrix surrounding X. laevis eggs consists of a vitelline envelope and a jelly coat. The jelly coat contains three morphologically distinct layers designated J1, J2, and J3 from the innermost to the outermost and is composed of 9-11 distinct glycoproteins. Each jelly layer is known to have specific functions in the fertilization of the egg. We developed a rapid method to separate and identify the oligosaccharides from X. laevis egg jelly layers. Identification was based on the retention times in high-performance liquid chromatography (porous graphitized carbon column), exact masses, and tandem mass spectrometry. Over 40 neutral and 30 sulfated oligosaccharides were observed in the three jelly layers. Neutral oligosaccharide structures from different jelly layers were both unique and overlapping, while sulfated oligosaccharides were detected only in layers J1 and J2. Neutral oligosaccharides unique to jelly layer J3 and the combined layers J1+J2 had similar core structures and similar residues. However, differences between these two sets of unique oligosaccharides were also observed and were primarily due to the branching carbohydrate moieties rather than the core structures.

Effect of sperm concentration, medium osmolality and oocyte storage on artificial fertilisation success in a myobatrachid frog (Limnodynastes tasmaniensis)

The present study optimised artificial fertilisation and oocyte storage conditions in Limnodynastes tasmaniensis (Myobatrachidae). Data on general reproductive biology, the effect of sperm motility and concentration, medium osmolality and oocyte storage on artificial fertilisation success are presented. Egg number was most strongly correlated with bodyweight (r = 0.819). Sperm yield was correlated with testes weight (r = 0.827), which was strongly correlated with snout–vent length (r = 0.772). Optimal artificial fertilisation occurred in 0–7 mOsm kg–1 amphibian Ringer, similar to ranid, bufonid and hylid species. High fertilisation rates were achieved using spermatozoa with little forwards progressive motility at comparatively low concentrations (3 × 104 sperm cells mL–1) and with no relationship between percentage sperm motility and fertilisation success (correlation of fertilisation rate with sperm motility after activation: r = –0.145). Oocytes stored in 5 mOsm kg–1 solutions showed no significant decline in fertilisability after 2 h, showing that swelling of the jelly surrounding the eggs does not prevent sperm from fusing with the oocyte in this species. Fertilisability of oocytes was extended to > 4 h in medium to high osmolality solutions (124–271 mOsm kg–1). These data allow for the future use of L. tasmaniensis in developing assisted reproductive technology protocols for foam-nesting myobatrachid species, many of which are now threatened with extinction in the wild.

Species specificity of O-linked carbohydrate chains of the oviducal mucins in amphibians: structural analysis of neutral oligosaccharide alditols released by reductive beta-elimination from the egg-jelly coats of Rana clamitans

The extracellular matrix (the so-called jelly coat) surrounding amphibian eggs mainly comprises highly O-glycosylated proteins. These oviducal mucins have an important role in the fertilization process, and their carbohydrate chains are remarkably species-specific. Alkaline reductive treatment of the jelly-coat material of the frog Rana clamitans led to the release of oligosaccharide alditols. The neutral oligosaccharide alditols were fractionated and purified by successive chromatographic techniques. The structures of 27 of them, ranging from three to sixteen monosaccharides, were established by a combination of NMR spectroscopy, methylation analyses and matrix-assisted laser-desorption ionization-time of flight MS. Typically, some of the neutral compounds appeared to possess the core structure: Gal(beta1-3)[GlcNAc(beta1-6)]Gal(beta1-3)[GlcNAc(beta1-6)]GalNAc-ol (where GalNAc-ol represents N-acetylgalactosaminitol). Moreover, a novel type of chain termination, characterized by an unusual sequence [Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-3/4)] was observed. Indeed, the most complex representative structure of this series was found to be: Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-3)[Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-4)GlcNAc(beta1-6)]Gal(beta1-3)[Fuc(alpha1-2)Gal(alpha1-3)Gal(alpha1-4)Gal(beta1-4)GlcNAc(beta1-6)]GalNAc-ol.

Xenopus laevis egg jelly contains small proteins that are essential to fertilization

The eggs of Xenopus laevis are surrounded by investment layers of egg jelly that interact with the sperm immediately prior to fertilization. Components of these egg jelly layers are necessary for the fertilization of the egg by incoming sperm. Eggs which are stripped of their jelly layers are refractile to fertilization by sperm, but the addition of solubilized jelly promotes fertilization. We have shown previously that the egg jelly layers are composed of a fibrous network of glycoconjugates which loosely hold smaller diffusible components. Extracts of these diffusible components were prepared by incubation of freshly ovulated eggs in high-salt buffers for 12 h at 4 degrees C. This diffusible component extract, when incubated with sperm, promoted the sperm's ability to fertilize dejellied eggs in a dose-dependent manner. In contrast, the high-molecular-weight "structural" glycoconjugates of jelly that remain after extraction of the diffusible components did not increase fertilization efficiency of dejellied eggs nor did nonspecific proteins, carbohydrate polymers, or organic polymers. The diffusible components, analyzed by SDS-PAGE, consisted of a mixture of proteins from 4 to 180 kDa. The protein responsible for fertilization rescue appeared to be <50 kDa and appeared to self-aggregate or to bind to larger proteins. This protein component was required during sperm binding to the egg, its action required an intact egg vitelline envelope, and its action was independent of large soluble polymers such as Ficoll.

Distribution of lectin binding sites in Xenopus laevis egg jelly

Eggs from the anuran Xenopus laevis are surrounded by a thick jelly coat that is required during fertilization. The jelly coat contains three morphologically distinct layers, designated J1, J2, and J3. We examined the lectin binding properties of the individual jelly coat layers as a step in identifying jelly glycoproteins that may be essential in fertilization. The reactivity of 31 lectins with isolated jelly coat layers was examined with enzyme-linked lectin-assays (ELLAs). Using ELLA we found that most of the lectins tested showed some reactivity to all three jelly layers; however, two lectins showed jelly layer selectivity. The lectin Maackia amurensis (MAA) reacted only with J1 and J2, while the lectin Trichosanthes kirilowii (TKA) reacted only with J2 and J3. Some lectins were localized in the jelly coat using confocal microscopy, which revealed substantial heterogeneity in lectin binding site distribution among and within jelly coat layers. Wheat germ agglutinin (WGA) bound only to the outermost region of J3 and produced a thin, but very intense, band of fluorescence at the J1/J2 interface while the remainder of J2 stained lightly. The lectin MAA produced an intense fluorescence-staining pattern only at the J1/J2 interface. Several lectins were also tested for the ability to inhibit fertilization. WGA, MAA, and concanavalin A significantly inhibited fertilization and WGA was found to block fertilization by preventing sperm from penetrating the jelly. Using Western blotting, we identified high-molecular-weight components in J1 and J2 that may be important in fertilization.

Isolation of the O-glycosidically linked oligosaccharides obtained by alkaline borohydride degradation from oviducal mucins of the toad Bufo bufo

A combination of normal-phase high-performance liquid chromatography (HPLC) on amino-bonded silica and reversed-phase HPLC on octadecylsilica has been used to separate the reduced oligosaccharides produced by alkaline borohydride degradation of oviducal mucins obtained from the jelly coat of Bufo bufo. The former technique provides suitable separation on the basis of molecular size, while the latter method offers selectivity for stereoisomers. Thirty-four compounds, ranging in size from a trisaccharide to a dodecaoligosaccharide, have been isolated preparatively using a Supelcosyl LC-NH2 normal-phase column eluted with aqueous acetonitrile and a Zorbax ODS reversed-phase column eluted with water.

Structural analysis of a new series of oligosaccharide-alditols released by reductive beta-elimination from oviducal mucins of Rana utricularia

Egg jelly coats from Rana utricularia are formed by components secreted along the oviduct. These secretion products overlay the oocytes as they pass along the different oviducal portions. In this study, carbohydrate chains of the jelly coat surrounding the eggs of R. utricularia were released by alkali/borohydride treatment. Fractionation of O-linked oligosaccharide-alditols was achieved by a combination of chromatographic techniques comprising anion-exchange chromatography, gel-permeation chromatography and HPLC on a silica column bonded with aminopropyl groups. Structural characterization was performed by one- and two-dimensional 1H-NMR spectroscopy in combination with matrix-assisted laser-desorption ionization-time of flight MS and methylation analysis. Ten oligosaccharide structures possessing a core consisting of Galbeta(1-->3)GalNAc-ol with or without branching through a GlcNAc residue linked beta(1-->6) to the GalNAc residue (core type 2 or core type 1 respectively) are described. The most representative carbohydrate sequences are: GlcNAc(beta1-3)[Fuc(alpha1-4)]GlcNAc, GalNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)GlcNAc(beta1-3)GlcNAc and Gal(beta1-3)GlcNAc(alpha1-3)[Fuc(alpha1-2)]Gal(beta1-4)GlcNAc. The carbohydrate chains isolated from R. utricularia are quite different from those found in other amphibian species, in which the presence of species-specific material has been characterized. Since the jellies surrounding amphibian eggs are involved in egg-sperm interactions, these structural investigations can provide biochemical support for investigation of the fertilization process.

Inositol 1,4,5-trisphosphate mass changes from fertilization through first cleavage in Xenopus laevis

After fertilization in Xenopus laevis, inositol 1,4,5-trisphosphate (IP3) mass increased from 53 to 261 fmol/cell and returned to near basal by 10 min after insemination. IP3 was also elevated over control egg levels during first mitosis and first cleavage. Because IP3 levels and the fertilization calcium wave decline at about the same time and because calcium ionophore or pricking the egg increased IP3, the fertilization calcium wave may be due to calcium-induced IP3 production. In addition, the onset of sperm motility was associated with an increase, whereas the acrosomal reaction was accompanied by a decrease in IP3 mass. Combining our published data with this report, the first chronology of the levels of IP3 from the induction of meiosis (maturation) through fertilization and cleavage in one cellular system is summarized. These data suggest an in vivo dose response for IP3 and calcium release. A small (17 fmol/cell) IP3 change during the induction of meiosis may not be associated with a calcium change. Larger IP3 changes at cleavage (40 fmol/cell) and mitosis (125 fmol/cell) are associated with localized small calcium increases, whereas the largest IP3 change (208 fmol/cell) is associated with the large calcium increase at fertilization.

Purification, physicochemical characterization, and immunohistochemical localization of a major 11.7 S glycoprotein from the jelly coats of the anuran Lepidobatrachus laevis

Embryos of the frog Lepidobatrachus laevis are encased by a fertilization envelope and two jelly layers, termed J1 (innermost) and J2 (outermost). From preparations of total jelly solubilized from cleavage-stage embryos by a solution of alkaline beta-mercaptoethanol we have purified one jelly coat glycoprotein to homogeneity via FPLC gel permeation chromatography on Superose 6H. The purified glycoprotein was 94% protein and 6% carbohydrate, had an s0(20),w of 11.7 S, with a molecular weight of 245,000 measured by sedimentation equilibrium and 263,000 by gel permeation chromatography. SDS-PAGE revealed that the glycoprotein is composed of a single subunit near 29,700 molecular weight; thus we propose that eight of these subunits comprise the native molecule. Amino acid analysis of the glycoprotein indicated a high content of Glx + Asx (32.4 mole%), a low content of basic amino acids (Arg + Lys = 12.2 mole%), and a single cysteine residue per subunit. The N-terminal amino acid was threonine and the sequence of the first twenty amino acids was determined. Monospecific antisera to the glycoprotein were prepared in rabbits and were used to immunohistochemically localize the glycoprotein throughout the matrix of both jelly layers. Antiserum against the glycoprotein had virtually no effect on the fertilizability of jellied eggs in vitro; thus we hypothesize that the glycoprotein fulfills a structural role in both jelly layers.

Stepwise transformation of the vitelline envelope of Xenopus eggs at activation: a quick-freeze, deep-etch analysis

The extracellular matrix of Xenopus laevis eggs was analyzed at fixed intervals after prick-activation using quick-freeze, deep-etch, rotary-shadow electron microscopy. This technique revealed that the modifications of the matrix seen at fertilization do not occur simultaneously, but that instead there is an orderly progression of alterations at activation. The first modification, conversion of the vitelline envelope (VE) to the altered vitelline envelope (VE), occurs within 2 to 3 min after activation. Intermediate stages of the VE to VE transformation can be visualized traveling around the egg in a wave-like fashion. Upon completion of the wave, the loosely woven outer surface of the VE, believed to be the prefertilization layer, remains unaltered. Subsequent formation of the fertilization (F) layer at this VE-jelly interface occurs between 4 and 8 min postactivation. Finally, between 10 and 15 min postactivation, the smooth (S) layer forms on the tips of the microvilli and surrounds the entire egg.

Identification of Xenopus laevis sperm and egg envelope binding components on nitrocellulose membranes

Interacting egg envelope and sperm surface components were identified for Xenopus laevis using blotting methods. Sperm were extracted with sodium dodecyl sulfate (SDS), the extracted proteins separated by gel electrophoresis and blotted, and the blots treated with 125I-labeled heat solubilized envelopes. The converse experiment was also performed where envelope components were separated by gel electrophoresis, blotted, and the blots treated with 125I-labeled sperm components. Blotted sperm components with apparent molecular weights of 14K, 19K, 25K, and 35K selectively bound the solubilized envelopes. All of the envelope binding components were found to be localized on the sperm surface by radioiodinating intact sperm using Iodo-Gen. The blotted egg envelope component with an apparent molecular weight of 37K selectively bound to solubilized sperm components, and this binding was due to the protein moiety of the glycoprotein. 125I-labeled heat solubilized envelopes from unfertilized and fertilized eggs showed the same pattern of binding to blotted sperm components. Selected sulfated carbohydrates (fucoidan, dextran sulfate, and heparin, but not chondroitin sulfate) inhibited fertilization and binding of 125I-labeled heat solubilized envelopes to blotted sperm extract. Thus, the binding of heat solubilized envelopes to electrophoretically separated and blotted sperm proteins may reflect cellular interactions.

Biochemical studies of the envelope transformations in Xenopus laevis eggs

The envelopes that enclose the eggs of the amphibian Xenopus laevis were isolated and examined for biochemical correlates of the ultrastructural and sperm penetrability differences among the coelomic egg envelope (CE), the vitelline envelope (VE), and the fertilization envelope (FE). By sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), the 43,000 molecular weight glycoproteins of CEs were found to be converted to components with molecular weights of 41,000 in VEs; also, a protein with a molecular weight of 57,000 was added to the envelope during the CE-to-VE conversion. The molecular weights of two components decreased during the VE-to-FE conversion, from 69,000 and 64,000 in the VE to 66,000 and 61,000 in the FE. Components from the cortical granules and the innermost jelly coat were also added to the newly-formed FE. As detected by iodination with lactoperoxidase or IODOGEN, both the CE-to-VE and the VE-to-FE conversions caused conformational changes in envelope glycoproteins. Peptide mapping demonstrated that the 43,000 molecular weight components of CE were precursors to the 41,000 molecular weight components of VE and the 69,000 and 64,000 molecular weight components of VE were precursors to the 66,000 and 61,000 molecular weight components of FE. The CE-to-VE conversion presumably occurs in the first portion of the oviduct. Experiments probing the VE-to-FE conversion demonstrated the need for an intact jelly coat for the molecular weight changes to occur. Sperm were not required for the envelope alteration; the SDS-PAGE pattern of envelopes from jellied eggs activated with the Ca++-ionophore A23187 were indistinguishable from the FE. These studies show that there are molecular correlates of the morphological and biological differences among the envelopes. The CE-to-VE and the VE-to-FE conversions follow a similar pattern: in both cases, material is added to the envelope and there are changes in the molecular weights of some of the components.

The role of oviducal secretions in mediating gamete fusion in the toad, Bufo bufo japonicus

A fertilizing sperm of the anuran amphibians has to pass through the jelly envelopes and the vitelline envelope (VE) before making a successful fusion with the egg plasma membrane. Of these the jelly envelopes, secreted by the long pars convoluta (PC) portion of the oviduct, have long been known to be indispensable for the sperm entrance in the egg. The most recent experiments employing dejellied uterine eggs of the toad, Bufo bufo japonicus, revealed that the jelly plays its role in fertilization by its unique capacity of retaining divalent cations (Ca2+ and/or Mg2+) which are essential for a fertilizing sperm. There are other lines of evidence which implicate that the secretions of the uppermost portion of oviduct, p. recta (PR), render the VE penetrable by sperm. We show that the secretory granules (PRG) isolated from PR of ovulating Bufo females by centrifugation in Percoll possess such biological activities as an increase of fertilizability of coelomic eggs and the induction of both the acrosome reaction and a release of the VE lysin from sperm. In addition, the activities of the PRG are inhibited by trypsin inhibitors, and this trypsin-like activity is dependent on Ca2+. These results, combined with the previous immunohistochemical demonstration of the deposition of PR-substance(s) in the VE, lead us to propose that a fertilizing toad sperm is acrosome-reacted in response to the PRG substance deposited in the VE and finds a way of traversing the VE by the released lysin, both of which may be dependent on Ca2+ supplied by jelly envelopes, the product of PC.

Peptides associated with eggs: mechanisms of interaction with spermatozoa

Speract (Gly-Phe-Asp-Leu-Asn-Gly-Gly-Gly-Val-Gly), a peptide obtained from the culture medium of Strongylocentrotus purpuratus eggs, stimulates the respiration and motility of S. purpuratus spermatozoa under appropriate conditions. Resact (Cys-Val-Thr-Gly-Ala-Pro-Gly-Cys-Val-Gly-Gly-Gly-Arg-LeuNH2), a peptide obtained from Arbacia punctulata eggs also stimulates the metabolism and motility of A. punctulata spermatozoa, however, it fails to stimulate S. purpuratus spermatozoa. Early biochemical responses of the spermatozoa to the egg peptides include a net H+ efflux and elevations of cyclic AMP and cyclic GMP concentrations. In addition, in A. punctulata spermatozoa, a major plasma membrane protein is modified in response to resact such that its apparent molecular weight shifts from 160,000 to 150,000. If cells are incubated with 32P, the 160,000 molecular weight form of the protein becomes radiolabeled; subsequent addition of resact causes a rapid loss of 32P from the protein. The plasma membrane protein appears to be the enzyme, guanylate cyclase; coincident with the shift in apparent molecular weight, enzyme activity decreases by as much as 90%. Since speract fails to cause these responses in A. punctulata, it can be concluded that the events are receptor-mediated.

Urodele egg jelly and fertilization

Fertilization of urodele amphibians is physiologically polyspermic. These amphibians lack sperm entry blocking mechanisms at the egg surface, such as a cortical reaction or a membrane depolarization. Although, egg jelly is necessary for sperm capacitation, a late block to sperm entry does occur about 30 min after fertilization at a precise interface between jelly layers. The jelly is secreted by oviductal cells. In order to investigate its role in fertilization, we studied some biochemical properties of the oviductal secretions of eight species. In double diffusion experiments on agarose plates, some components secreted by the anterior and the middle parts of the oviduct interacted together and formed precipitin lines. This reaction might be responsible for the formation of the dense zone that delimits the capsular chamber. A hemagglutinating activity was found in the anterior or in the posterior part of the oviduct depending on the species. A 18K or 26K lectin was purified respectively from the oviduct of Ambystoma mexicanum and Pleurodeles waltl. In both species, the site where the late block to sperm entry is operative was spatially related to the location of the lectin in the jelly. However, sperm in contact with the purified lectins did not undergo any visible morphological change.

Toad egg-jelly as a source of divalent cations essential for fertilization

Dejellied uterine eggs of the toad Bufo bufo japonicus are not fertilizable in 1/20 De Boer's solution (1/20 DB), but are fertilized when inseminated in a uv-solubilized jelly (UVJ) or the dialyzate of UVJ (UVJD). The present study was carried out to define this fertilization-supporting activity of egg-jelly. Dejellied eggs were fertilized in a high frequency when inseminated in a medium containing the ashes obtained by heating UVJD at 600 degrees C for 16 hr. Similarly, a reconstituted salt solution (RSS), which mimics the ionic composition of UVJD, supported a high rate of fertilization. To be effective in fertilization, however, RSS had to be present at the time of insemination. Analyses of individual salts revealed that dejellied eggs are successfully fertilized in CaCl2 and/or MgCl2 at 1-5 mM, only slightly in KCl at 10 mM, but not at all in NaCl at any of the concentrations tested. The activity of UVJD was lost reversibly when divalent cations were chelated by EDTA. The fertilization of dejellied eggs is therefore possible in a medium without any organic components of egg-jelly, provided that 2-5 mM Ca2+ or Mg2+ is present. Sperm were motile in media containing cations below 20-25 mM, regardless of the ionic composition. The egg-jelly possessed cations in a concentration of about 130 mM, but most ions were lost from intact jelly on immersion of eggs in water for 2-3 min, accompanied by the acquisition of fertilizability by sperm. Examination of the behavior of salts on dialysis or gel-filtration of jelly molecules revealed that the jelly retains Ca2+ and Mg2+, and possibly K+ as well, but not Na+ and Cl-. We propose that toad egg-jelly plays a function in fertilization by retaining Ca2+ and/or Mg2+ around each egg at the level necessary for successful sperm entrance into the egg.

Fertilization of investment-free Xenopus eggs

The vitelline envelope of unfertilized Xenopus egg can be removed manually after treating the dejellied eggs for 10 min with 20% (w/v) sucrose in F-1 saline. Fertilization occurred in 52% of the eggs denuded in this way when UV-solubilized jelly was added to the sperm-egg mixture; without the jelly the level of fertilization was only 6%. Fertilization did not occur synchronously in the denuded eggs; the average delay between insemination and fertilization was 19 +/- 18 min.

An oviducal enzyme isolated by affinity chromatography which acts upon the vitelline envelope of Bufo arenarum coelomic oocytes

A trypsin-like oviducal proteinase acting upon the vitelline envelope of Bufo arenarum coelomic oocytes has been purified to apparent homogeneity by gel filtration on Sephadex G-200 and by affinity chromatography on a column of Sepharose 4-B containing covalently bound concanavlin A (Con A). The biologically active molecule migrated as a single band of protein upon SDS polyacrylamide gel electrophoresis.

Alteration of structure and penetrability of the vitelline envelope after passage of eggs from coelom to oviduct in Xenopus laevis

The vitelline envelope (VE) that surrounds an egg released from the ovary into the coelom of Xenopus laevis differs markedly, in structure and penetrability, from the VE surrounding an oviposited egg. In a coelomic egg, the filaments that form the VE are arranged in distinct fascicles or bundles. The exterior surface of the VE is irregular in contour and is permeated by channels. In an oviposited egg, the filaments are evenly dispersed and lack a fasciculated arrangement; the exterior surface is smooth and no channels are present. The fascicular arrangement of fibrils in the coelomic VE is maintained only at neutral pH, and is not visibly altered by the cortical reaction. VEs from coelomic eggs retain their fasciculated morphology after isolation from the egg. In an in vitro test system, sperm penetrated VEs isolated from oviposited eggs, but failed to penetrate VEs isolated from coelomic eggs. The structural transformation of the VE from the coelomic type to the oviposited type occurs in the first 1-cm segment of the oviduct, prior to addition of jelly to the egg. Neither intact jelly, solubilized jelly, nor jelly extracts were capable of altering the structural organization of coelomic VEs, suggesting that the structural transformation of the VE is effected by some oviducal factor other than jelly.

The macromolecular composition of Xenopus laevis egg jelly coat

The three morphologically and functionally distinct jelly coat layers of Xenopus laevis eggs, J1, J2, and J3, were separated by manual dissection, solubilized with dithiothreitol, and physicochemically analyzed. The chemical composition of the three jelly layers varied from 37 to 48% protein and 63 to 52% carbohydrate. The carbohydrate consisted of hexosamines, galactose, and fucose. Some of the carbohydrate in each of the jelly layers was covalently linked to protein through O-glycosidic bonds as beta elimination of the carbohydrate moiety in the presence of alkali was observed. In agreement with a previous finding, covalently attached sulfate was localized within the innermost jelly coat layer, J1. Cellulose acetate electrophoresis at pH 8.0 resolved a total of nine macromolecular components from the three jelly coat layers differentially staining for protein and carbohydrate: J1 yielded two anodically migrating components; the middle layer J2 yielded two cathodically migrating macromolecular components; the outermost layer J3 contained five species, three anodic and two cathodic. Sodium dodecyl sulfate agarose gel electrophoresis analysis yielded nine unique species, six of which stained coincidently for protein and carbohydrate. Immunoelectrophoresis and Ouchterlony double diffusion analyses using antiserum to total jelly components resolved nine different antigenic species with cross-reactivity between one or two macromolecules in layers J1 and J3. Analytical sedimentation velocity centrifugation revealed eight distinct species all of which exhibited hypersharp schlieren patterns and whose s20,w values were highly concentration dependent. On the basis of these analyses, Xenopus laevis egg jelly layers are composed of at least 8-9 distinct macromolecular species. The majority of these macromolecules are uniquely associated with different jelly coat layers.

Agglutination of jelly coat and cortical granule components and the block to polyspermy in the amphibian Xenopus laevis

A block to polyspermy in amphibians is established at fertilization by the conversion of the vitelline envelope to the fertilization envelope. In Xenopus laevis a major ultrastructural change in the envelope at fertilization is the appearance of an electron-dense layer, termed the F layer, between the envelope and the inner-most jelly coat layer, J(1). The F layer is derived, at least in part, from materials released from the cortical granules. Further definition of the origin and chemical nature of the F layer was sought by using isolated cortical granule (CG) exudate and jelly coat layer J(1). In double diffusion experiments, the isolated components interacted in an agglutination reaction producing a band of precipitation. The agglutination involved alpha-galactoside residues and metal ions (Ca(++)). Employing chemically modified jelly, we demonstrated that sulfhydryl-disulfide interchanges were not involved in the agglutination and, with (35)S-labeled jelly, that the agglutinating J(1) component possessed sulfate esters. Both the CG exudate and the J(1) components contained carbohydrate, as evidenced by their lectin reactivity. A number of ionic polymers, both natural and synthetic, were tested as chemical analogs of CG exudate and J(1); none gave an agglutination band. Dissolved jelly coat material from eggs of two different species of frogs agglutinated with CG exudate, while jelly from sea urchin eggs and hyaluronic acid from mammalian eggs did not. Thus, the agglutination reaction was chemically and phylogenetically specific. An electron-dense layer, similar to the F layer, formed on the outer of the vitelline envelope when jellied unfertilized eggs were immersed in CG exudate; such eggs were not fertilizable. We suggest that in Xenopus laevis, and perhaps other organisms as well, an agglutination type of reaction between cortical granule components and egg integuments is a participant in the structural and molecular events establishing a block to polyspermy.