Sperm protein "DE" mediates gamete fusion through an evolutionarily conserved site of the CRISP family

Expression of helminth genes in Leishmania: an experimental transfection system to test immunological function

Functional analysis of genes from parasitic helminths requires, at the present time, heterologous expression. We have adapted the well-characterized system of transfection in Leishmania protozoal parasites, as a means of analysing the effect of single filarial genes on the mammalian immune system. For example, testing the function of the Brugia malayi abundant larval transcript (ALT) gene-transfected Leishmania mexicana were found to be significantly more virulent in macrophages in vitro. The course of infection in vivo is also aggravated by expression of the ALT gene. Examples are also given of transgenes which reduced in vitro growth within macrophages, as well as others which exert no effect on the protozoal parasitism. Thus, Leishmania transfection provides a tractable system to analyse helminth gene function within the context of the host immune system.

The conserved plant sterility gene HAP2 functions after attachment of fusogenic membranes in Chlamydomonas and Plasmodium gametes

The cellular and molecular mechanisms that underlie species-specific membrane fusion between male and female gametes remain largely unknown. Here, by use of gene discovery methods in the green alga Chlamydomonas, gene disruption in the rodent malaria parasite Plasmodium berghei, and distinctive features of fertilization in both organisms, we report discovery of a mechanism that accounts for a conserved protein required for gamete fusion. A screen for fusion mutants in Chlamydomonas identified a homolog of HAP2, an Arabidopsis sterility gene. Moreover, HAP2 disruption in Plasmodium blocked fertilization and thereby mosquito transmission of malaria. HAP2 localizes at the fusion site of Chlamydomonas minus gametes, yet Chlamydomonas minus and Plasmodium hap2 male gametes retain the ability, using other, species-limited proteins, to form tight prefusion membrane attachments with their respective gamete partners. Membrane dye experiments show that HAP2 is essential for membrane merger. Thus, in two distantly related eukaryotes, species-limited proteins govern access to a conserved protein essential for membrane fusion.

Impaired sperm fertilizing ability in mice lacking Cysteine-RIch Secretory Protein 1 (CRISP1)

Mammalian fertilization is a complex multi-step process mediated by different molecules present on both gametes. Epididymal protein CRISP1, a member of the Cysteine-RIch Secretory Protein (CRISP) family, was identified by our laboratory and postulated to participate in both sperm-zona pellucida (ZP) interaction and gamete fusion by binding to egg-complementary sites. To elucidate the functional role of CRISP1 in vivo, we disrupted the Crisp1 gene and evaluated the effect on animal fertility and several sperm parameters. Male and female Crisp1(-/-) animals exhibited no differences in fertility compared to controls. Sperm motility and the ability to undergo a spontaneous or progesterone-induced acrosome reaction were neither affected in Crisp1(-/-) mice. However, the level of protein tyrosine phosphorylation during capacitation was clearly lower in mutant sperm than in controls. In vitro fertilization assays showed that Crisp1(-/-) sperm also exhibited a significantly reduced ability to penetrate both ZP-intact and ZP-free eggs. Moreover, when ZP-free eggs were simultaneously inseminated with Crisp1(+/+) and Crisp1(-/-) sperm in a competition assay, the mutant sperm exhibited a greater disadvantage in their fusion ability. Finally, the finding that the fusion ability of Crisp1(-/-) sperm was further inhibited by the presence of CRISP1 or CRISP2 during gamete co-incubation, supports that another CRISP cooperates with CRISP1 during fertilization and might compensate for its lack in the mutant mice. Together, these results indicate that CRISP proteins are players in the mammalian fertilization process. To our knowledge this is the first knockout mice generated for a CRISP protein. The information obtained might have important functional implications for other members of the widely distributed and evolutionarily conserved CRISP family.

Xenopus tropicalis allurin: expression, purification, and characterization of a sperm chemoattractant that exhibits cross-species activity

Previously we reported the identification of the first vertebrate sperm chemoattractant, allurin, in the frog Xenopus laevis (Xl) and demonstrated that it was a member of the CRISP family of proteins. Here we report identification, purification, and characterization of Xenopus tropicalis (Xt) allurin, a homologous protein in X. tropicalis. "Egg water" as well as purified allurin from both species exhibit efficient cross-species sperm chemoattractant activity. Western blots show that Xt egg water contains a single anti-allurin cross-reactive protein whose molecular weight (20,497 Da by MALDI MS) agrees well with the molecular weight of the hypothetical gene product for a newly recognized "Crisp A" gene in the X. tropicalis genome. A recombinant form of the protein, expressed in 3T3 cells, exhibits chemoattraction for both Xt and Xl sperm and cross reacts with anti-allurin antibodies. Examination of Crisp protein expression in the Xt oviduct using RT-PCR showed that of five documented Xt Crisp genes (Crisps 2, 3, LD1, LD2 and A) only Crisp A was expressed. In contrast, Crisp 2, Crisp 3, Crisp LD1, and Crisp LD2, but not Crisp A, were all found to be expressed in the Xt testes while subsets of Crisp proteins where expressed in the Xt ovary. These data suggest that Crisp proteins in amphibians may play multiple roles in sperm production, maturation and guidance just as they are thought to in mammals indicating that Crisp protein involvement in reproduction may not be limited to mammals.

Cloning and isolation of a Conus cysteine-rich protein homologous to Tex31 but without proteolytic activity

We cloned and isolated a cysteine-rich protein, designated Mr30, from Conus marmoreus. Mr30 belongs to the cysteine-rich secretory protein family that is highly homologous to Tex31 previously obtained from Conus textile and reported as a protease responsible for processing of pro-conotoxins. Mr30, purified by a procedure similar to that of Tex31, indeed showed low proteolytic activity. However, further investigations revealed that the detected protease activity actually resulted from a trace amount of protease(s) contamination rather than from Mr30 itself. This finding led us to rethink the role of conus cysteine-rich secretory proteins: they were probably not responsible for the processing of pro-conotoxins as previously deduced, but their real biological functions remained to be clarified.

Participation of epididymal cysteine-rich secretory proteins in sperm-egg fusion and their potential use for male fertility regulation

Rat protein DE is an androgen-dependent cysteine-rich secretory protein (CRISP) synthesized by proximal epididymal regions. DE, also known as CRISP-1, is localized on the equatorial segment of acrosome-reacted spermatozoa and participates in gamete fusion through binding to egg complementary sites. Immunization of rats with DE inhibits fertility and sperm fusion ability, suggesting that DE represents a good epididymal contraceptive target. Recombinant DE fragments and synthetic peptides revealed that DE binds to the egg via a 12-amino acid region of an evolutionarily conserved motif, Signature 2 (S2). The ability of other CRISP to bind to the rat egg was correlated with their S2 amino acid sequences. Although testicular protein Tpx-1 (CRISP-2) was capable of binding to rodent eggs, human epididymal AEG-related protein (ARP) and helothermine (from lizard saliva) were not. The S2 region presented only two substitutions in Tpx-1 and four in ARP and helothermine, compared with the DE S2, suggesting that this amino acid sequence was relevant for egg interaction. Studies with Tpx-1 and anti-Tpx-1 revealed the participation of this protein in gamete fusion through binding to complementary sites in the egg. In competition studies, DE reduced binding of Tpx-1 dose-dependently, indicating that both CRISP share the egg complementary sites. That anti-DE and anti-Tpx-1 inhibit sperm-egg fusion while recognizing only the corresponding proteins, suggests functional cooperation between these homologous CRISP to ensure fertilization success. These results increase our understanding of the molecular mechanisms of gamete fusion and contribute to the development of new and safer fertility regulating methods.

Structure and function of epididymal protein cysteine-rich secretory protein-1

Cysteine-rich secretory protein-1 (CRISP-1) is a glycoprotein secreted by the epididymal epithelium. It is a member of a large family of proteins characterized by two conserved domains and a set of 16 conserved cysteine residues. In mammals, CRISP-1 inhibits sperm-egg fusion and can suppress sperm capacitation. The molecular mechanism of action of the mammalian CRISP proteins remains unknown, but certain non-mammalian CRISP proteins can block ion channels. In the rat, CRISP-1 comprises two forms referred to as Proteins D and E. Recent work in our laboratory demonstrates that the D form of CRISP-1 associates transiently with the sperm surface, whereas the E form binds tightly. When the spermatozoa are washed, the E form of CRISP-1 persists on the sperm surface after all D form has dissociated. Cross-linking studies demonstrate different protein-protein interaction patterns for D and E, although no binding partners for either protein have yet been identified. Mass spectrometric analyses revealed a potential post-translational modification on the E form that is not present on the D form. This is the only discernable difference between Proteins D and E, and presumably is responsible for the difference in behavior of these two forms of rat CRISP-1. These studies demonstrate that the more abundant D form interacts with spermatozoa transiently, possibly with a specific receptor on the sperm surface, consistent with a capacitation-suppressing function during sperm transit and storage in the epididymis, and also confirm a tightly bound population of the E form that could act in the female reproductive tract.

A novel function for CRISP1 in rodent fertilization: involvement in sperm-zona pellucida interaction

Epididymal protein CRISP1 participates in rat and mouse gamete fusion through its interaction with complementary sites on the egg surface. Based on in vivo observations, in the present study we investigated the possibility that CRISP1 plays an additional role in the sperm-zona pellucida (ZP) interaction that precedes gamete fusion. In vitro fertilization experiments using zona-intact rat and mouse eggs indicated that the presence of either an antibody against rat CRISP1 (anti-CRISP1) or rat native CRISP1 (rCRISP1) during gamete co-incubation produced a significant decrease in the percentage of fertilized eggs. However, differently to that expected for a protein involved in gamete fusion, no accumulation of perivitelline sperm was observed, suggesting that the inhibitions occurred at the sperm-ZP interaction level. Bacterially expressed recombinant CRISP1 (recCRISP1) also significantly inhibited egg fertilization. In this case, however, an increase in the number of perivitelline sperm was observed. Subsequent experiments evaluating the effect of anti-CRISP1 or rCRISP1 on the number of sperm bound per egg indicated that the protein is involved in the initial step of sperm-ZP binding. In agreement with these functional studies, indirect immunofluorescence experiments revealed that although rCRISP1 is capable of binding to both the ZP and the oolema, recCRISP1 only binds to the egg surface. The finding that deglycosylated rCRISP1 behaves as the untreated protein, whereas the heat-denatured rCRISP1 associated only with the oolema, indicates that the protein ZP-binding ability resides in the conformation rather than in the glycosydic portion of the molecule. The interaction between rCRISP1 and the ZP reproduces the sperm-ZP-binding behavior, as judged by the failure of the protein to interact with the ZP of fertilized eggs. Together, these results support the idea that CRISP1 participates not only in sperm-egg fusion but also in the prior stage of sperm-ZP interaction.

Seminal influences: Drosophila Acps and the molecular interplay between males and females during reproduction

Successful reproduction requires contributions from both the male and the female. In Drosophila, contributions from the male include accessory gland proteins (Acps) that are components of the seminal fluid. Upon their transfer to the female, Acps affect the female's physiology and behavior. Although primary sequences of Acp genes exhibit variation among species and genera, the conservation of protein biochemical classes in the seminal fluid suggests a conservation of functions. Bioinformatics coupled with molecular and genetic tools available for Drosophila melanogaster has expanded the functional analysis of Acps in recent years to the genomic/proteomic scale. Molecular interplay between Acps and the female enhances her egg production, reduces her receptivity to remating, alters her immune response and feeding behavior, facilitates storage and utilization of sperm in the female and affects her longevity. Here, we provide an overview of the D. melanogaster Acps and integrate the results from several studies that bring the current number of known D. melanogaster Acps to 112. We then discuss several examples of how the female's physiological processes and behaviors are mediated by interactions between Acps and the female. Understanding how Acps elicit particular female responses will provide insights into reproductive biology and chemical communication, tools for analyzing models of sexual cooperation and/or sexual conflict, and information potentially useful for strategies for managing insect pests.

Evidence for the Involvement of Testicular Protein CRISP2 in Mouse Sperm-Egg Fusion1

CRISP2, originally known as Tpx-1, is a cysteine-rich secretory protein specifically expressed in male haploid germ cells. Although likely to be involved in gamete interaction, evidence for a functional role of CRISP2 in fertilization still remains poor. In the present study, we used a mouse model to examine the subcellular localization of CRISP2 in sperm and its involvement in the different stages of fertilization. Results from indirect immunofluorescence and protein extraction experiments indicated that mouse CRISP2 is an intraacrosomal component that remains associated with sperm after capacitation and the acrosome reaction (AR). In vitro fertilization assays using zona pellucida-intact mouse eggs showed that an antibody against the protein significantly decreased the percentage of penetrated eggs, with a coincident accumulation of perivitelline sperm. The failure to inhibit zona pellucida penetration excludes a detrimental effect of the antibody on sperm motility or the AR, supporting a specific participation of CRISP2 at the sperm-egg fusion step. In agreement with this evidence, recombinant mouse CRISP2 (recCRISP2) specifically bound to the fusogenic area of mouse eggs, as previously reported for rat CRISP1, an epididymal protein involved in gamete fusion. In vitro competition investigations showed that incubation of mouse zona-free eggs with a fixed concentration of recCRISP2 and increasing amounts of rat CRISP1 reduced the binding of recCRISP2 to the egg, suggesting that the proteins interact with common complementary sites on the egg surface. Our findings indicate that testicular CRISP2, as observed for epididymal CRISP1, is involved in sperm-egg fusion through its binding to complementary sites on the egg surface, supporting the idea of functional cooperation between homologous molecules to ensure the success of fertilization.