Oviductin, the Xenopus laevis oviductal protease that processes egg envelope glycoprotein gp43, increases sperm binding to envelopes, and is translated as part of an unusual mosaic protein composed of two protease and several CUB domains

Seminal fluid proteins induce transcriptome changes in the Aedes aegypti female lower reproductive tract

BACKGROUND

Mating induces behavioral and physiological changes in the arbovirus vector Aedes aegypti, including stimulation of egg development and oviposition, increased survival, and reluctance to re-mate with subsequent males. Transferred seminal fluid proteins and peptides derived from the male accessory glands induce these changes, though the mechanism by which they do this is not known.

RESULTS

To determine transcriptome changes induced by seminal proteins, we injected extract from male accessory glands and seminal vesicles (MAG extract) into females and examined female lower reproductive tract (LRT) transcriptomes 24 h later, relative to non-injected controls. MAG extract induced 87 transcript-level changes, 31 of which were also seen in a previous study of the LRT 24 h after a natural mating, including 15 genes with transcript-level changes similarly observed in the spermathecae of mated females. The differentially-regulated genes are involved in diverse molecular processes, including immunity, proteolysis, neuronal function, transcription control, or contain predicted small-molecule binding and transport domains.

CONCLUSIONS

Our results reveal that seminal fluid proteins, specifically, can induce gene expression responses after mating and identify gene targets to further investigate for roles in post-mating responses and potential use in vector control.

Integrative analysis of transcriptomic data related to the liver of laying hens: from physiological basics to newly identified functions

Background

At sexual maturity, the liver of laying hens undergoes many metabolic changes to support vitellogenesis. In published transcriptomic approaches, hundreds of genes were reported to be overexpressed in laying hens and functional gene annotation using gene ontology tools have essentially revealed an enrichment in lipid and protein metabolisms. We reanalyzed some data from a previously published article comparing 38-week old versus 10-week old hens to give a more integrative view of the functions stimulated in the liver at sexual maturity and to move beyond current physiological knowledge. Functions were defined based on information available in Uniprot database and published literature.

Results

Of the 516 genes previously shown to be overexpressed in the liver of laying hens, 475 were intracellular (1.23–50.72 fold changes), while only 36 were predicted to be secreted (1.35–66.93 fold changes) and 5 had no related information on their cellular location. Besides lipogenesis and protein metabolism, we demonstrated that the liver of laying hens overexpresses several clock genes (which supports the circadian control of liver metabolic functions) and was likely to be involved in a liver/brain/liver circuit (neurotransmitter transport), in thyroid and steroid hormones metabolisms. Many genes were associated with anatomical structure development, organ homeostasis but also regulation of blood pressure. As expected, several secreted proteins are incorporated in yolky follicles but we also evidenced that some proteins are likely participating in fertilization (ZP1, MFGE8, LINC00954, OVOCH1) and in thyroid hormone maturation (CPQ). We also proposed that secreted proteins (PHOSPHO1, FGF23, BMP7 but also vitamin-binding proteins) may contribute to the development of peripheral organs including the formation of medullar bones to provide labile calcium for eggshell formation. Thirteen genes are uniquely found in chicken/bird but not in human species, which strengthens that some of these genes may be specifically related to avian reproduction.

Conclusions

This study gives additional hypotheses on some molecular actors and mechanisms that are involved in basic physiological function of the liver at sexual maturity of hen. It also revealed some additional functions that accompany reproductive capacities of laying hens, and that are usually underestimated when using classical gene ontology approaches.

Follicle cell trypsin-like protease HrOvochymase: Its cDNA cloning, localization, and involvement in the late stage of oogenesis in the ascidian Halocynthia roretzi

We previously reported that the sperm trypsin-like protease HrAcrosin and its precursor HrProacrosin participate in fertilization of the ascidian Halocynthia roretzi. The HrProacrosin gene is annotated in the H. roretzi genome database as Harore.CG.MTP2014.S89.g15383; our previously reported sequence of HrProacrosin gene appeared to include four nucleotides inserted near the 3'-end of HrProacrosin, resulting in a frame-shift mutation and a premature termination codon. The gene architecture of HrProacrosin and Harore.CG.MTP2014.S89.g15383 resembles that of Xenopus laevis ovochymase-1/OVCH1 and ovochymase-2/OVCH2, which encode egg extracellular polyproteases. Considering these new observations, we evaluated the cDNA cloning, expression, localization, and function of Harore.CG.MTP2014.S89.g15383, herein designated as HrOvochymase/HrOVCH. We found that HrOVCH cDNA consists of a single open reading frame of 1,575 amino acids, containing a signal peptide, three trypsin-like protease domains, and six CUB domains. HrOVCH was transcribed by the testis and ovary, but the majority of protein exists in ovarian follicle cells surrounding eggs. An anti-HrOVCH antibody inhibited elevation of the vitelline coat at a late stage of oogenesis, during the period when self-sterility is acquired. As trypsin inhibitors are reported to block the acquisition of self-sterility during oogenesis, whereas trypsin induces the acquisition of self-sterility and elevation of the vitelline coat in defolliculated ovarian eggs, we propose that HrOVCH may play a role in the acquisition of self-sterility by late-stage H. roretzi oocytes.

Mating-Induced Transcriptome Changes in the Reproductive Tract of Female Aedes aegypti

The Aedes aegypti mosquito is a significant public health threat, as it is the main vector of dengue and chikungunya viruses. Disease control efforts could be enhanced through reproductive manipulation of these vectors. Previous work has revealed a relationship between male seminal fluid proteins transferred to females during mating and female post-mating physiology and behavior. To better understand this interplay, we used short-read RNA sequencing to identify gene expression changes in the lower reproductive tract of females in response to mating. We characterized mRNA expression in virgin and mated females at 0, 6 and 24 hours post-mating (hpm) and identified 364 differentially abundant transcripts between mating status groups. Surprisingly, 60 transcripts were more abundant at 0hpm compared to virgin females, suggesting transfer from males. Twenty of these encode known Ae. aegypti seminal fluid proteins. Transfer and detection of male accessory gland-derived mRNA in females at 0hpm was confirmed by measurement of eGFP mRNA in females mated to eGFP-expressing males. In addition, 150 transcripts were up-regulated at 6hpm and 24hpm, while 130 transcripts were down-regulated at 6hpm and 24hpm. Gene Ontology (GO) enrichment analysis revealed that proteases, a protein class broadly known to play important roles in reproduction, were among the most enriched protein classes. RNAs associated with immune system and antimicrobial function were also up-regulated at 24hpm. Collectively, our results suggest that copulation initiates broad transcriptome changes across the mosquito female reproductive tract, “priming” her for important subsequent processes of blood feeding, egg development and immune defense. Our transcriptome analysis provides a vital foundation for future studies of the consequences of mating on female biology and will aid studies seeking to identify specific gene families, molecules and pathways that support key reproductive processes in the female mosquito.

Female post-mating behavior has important consequences for mosquito populations and their ability to transmit diseases. Male Aedes aegypti seminal fluid substances transferred during mating cause many important changes to female behavior and physiology, including blood feeding behavior, egg development, and oviposition. In an effort to understand how males induce these responses in Ae. aegypti females, we characterized the transcriptome changes that occur in the female reproductive tract at different time points after mating. We found several RNAs that are apparently transferred by the male, and 280 genes whose mRNA abundance in the female is affected by mating. The nature of the predicted products of many of these genes suggests roles in priming the reproductive tract for egg development, protecting the female against bacterial infections or processing the blood meal. This identification of mating-responsive genes provides information potentially useful for developing tools aimed at preventing disease transmission by manipulating female mosquitoes’ post-mating responses.

Dicalcin, a zona pellucida protein that regulates fertilization competence of the egg coat in Xenopus laevis

Fertilization is a highly coordinated process whereby sperm interact with the egg-coating envelope (called the zona pellucida, ZP) in a taxon-restricted manner, Fertilization triggers the resumption of the cell cycle of the egg, ultimately leading to generation of a new organism that contains hereditary information of the parents. The complete sperm-ZP interaction comprises sperm recognition of the ZP, the acrosome reaction, penetration of the ZP, and fusion with the egg. Recent evidence suggests that these processes involve oligosaccharides associated with a ZP constituent (termed ZP protein), the polypeptide backbone of a ZP protein, and/or the proper three-dimensional filamentous structure of the ZP. However, a detailed description of the molecular mechanisms involved in sperm-ZP interaction remains elusive. Recently, I found that dicalcin, a novel ZP protein-associated protein, suppresses fertilization through its association with gp41, the frog counterpart of the mammalian ZPC protein. This review focuses on molecular aspects of sperm-ZP interaction and describes the fertilization-suppressive function of dicalcin and associated molecular mechanisms. The amount of dicalcin in the ZP significantly correlates with alteration of the lectin-staining pattern within the ZP and the orientation pattern of ZP filaments, which may assist in elucidating the complex molecular mechanisms that underlie sperm-ZP interaction.

Fertilization competence of the egg-coating envelope is regulated by direct interaction of dicalcin and gp41, the Xenopus laevis ZP3

Fertilization begins with species-restricted interaction of sperm and the egg-coating envelope, which includes a three-dimensional meshwork of filaments composed of glycoproteins (called ZP proteins). Growing evidence has unveiled the molecular nature of ZP proteins; however, the structural property conferring fertilization competence to the egg-coating envelope remains unknown. Here, we show the molecular mechanism that mediates direct interaction between dicalcin, a novel fertilization-suppressive ZP protein-associated protein, and gp41, a Xenopus laevis ortholog of mammalian ZP3, and subsequently demonstrate the structural basis of the envelope for fertilization competence. The interactive regions between dicalcin and gp41 comprised six and nine amino acid residues within dicalcin and twenty-three within gp41. Synthetic peptides corresponding to these regions dramatically affected fertilization: treatment with dicalcin- or gp41-derived peptides decreased or increased fertilization rates, respectively. Prior application of these peptides caused distinct alterations in the in vivo lectin-staining pattern of the envelope as well. Transmission electron microscopy analysis revealed that the dicalcin-derived peptide induced the formation of a well-organized meshwork, whereas the gp41-derived peptide caused the formation of a significantly disorganized meshwork. These findings indicated that the fertilization competence of the egg-coating envelope is crucially regulated by the direct interaction between dicalcin and gp41.

The Family Secrets of Avian Egg-Specific Ovalbumin and Its Related Proteins Y and X

The ovalbumin gene family in Gallus gallus is composed of three homologous genes located within a 46 kb locus on chromosome 2: ovalbumin, ovalbumin-related protein Y (OVAY), and ovalbumin-related protein X (OVAX) genes. The expression of these genes in hen oviduct is under estrogen control, but their relative hormonal responsiveness and subsequent protein concentration in egg, is distinctive. Interestingly, all three proteins lack the classical signal peptide for secretion. Ovalbumin, OVAX, and OVAY belong to the serine protease inhibitor (serpin) family whose members share a common tertiary structure. Ovalbumin and OVAX are one of the few members of this family that do not express any protease inhibition activity whereas OVAY has been predicted to be inhibitory, by comparison with the consensus sequence for inhibitory serpins. In contrast to ovalbumin and OVAY, OVAX interacts with heparin, a negatively charged glycosaminoglycan, via a positively charged domain exposed at the surface of the molecule. Ovalbumin is the major egg white protein and might be a source of amino acids for the developing embryo. The physiological function of OVAY is not known, but recent data have revealed a possible role of this protein in early embryonic development. Considering the antibacterial activities of OVAX, this protein might play a role in egg defense. This review sheds light on the expression, biochemistry, and structural specificities of these three highly similar paralogs. It gives new clues in favor of diverging functions, which are likely to have arisen by duplication events from a common ancestral gene.

Structural analysis of toad oviductal mucosa in relation to jelly components secretion throughout the reproductive cycle

In amphibians, the components of the jelly coats that surround the oocytes at the time of fertilization and coordinate gamete interaction are secreted by the oviduct. We analysed the histological variations in the mucosa of the oviductal pars convoluta (PC) of Rhinella arenarum during the reproductive cycle and its relationship with secretion. During the preovulatory period, the mucosa reaches a high degree of morphological and functional development, with a large number of epithelial (ESC) and glandular secretory cells (GSC) loaded with contents that are secreted into the oviductal lumen. During the ovulatory period, the secretory cells (SC) of both layers present maximum secretory activity through apocrinia and merocrinia. While the ESC located at the tips of the folds release their content directly in contact with the oocytes, the GSC secrete material from the bottom of the epithelial folds that, by interaction with the secretion of the ESC in the lateral faces, form a product with a certain degree of organization. Secretion is a continuous process with formation of coats of increasing complexity from the intermediate proximal zone (IPZ) to the pars convoluta (pc) itself, and the passage of the oocyte is a requisite for the organization of the jelly coats around the gamete. During the early postovulatory period, although there is a marked decrease in the number and volume of the SC, the ESC still release material into the oviductal lumen. In the late postovulatory period the morphological characteristics of the PC begin to recovery although there is no evidence of secretion.

Transcriptomic profiling of proteases and antiproteases in the liver of sexually mature hens in relation to vitellogenesis

Background

Most egg yolk precursors are synthesized by the liver, secreted into the blood and transferred into oocytes, to provide nutrients and bioactive molecules for the avian embryo. Three hundred and sixteen distinct proteins have been identified in egg yolk. These include 37 proteases and antiproteases, which are likely to play a role in the formation of the yolk (vitellogenesis), as regulators of protein metabolism. We used a transcriptomic approach to define the protease and antiprotease genes specifically expressed in the hen liver in relation to vitellogenesis by comparing sexually mature and pre-laying chickens showing different steroid milieu.

Results

Using a 20 K chicken oligoarray, a total of 582 genes were shown to be over-expressed in the liver of sexually mature hens (1.2 to 67 fold-differences). Eight of the top ten over-expressed genes are known components of the egg yolk or perivitelline membrane. This list of 582 genes contains 12 proteases and 3 antiproteases. We found that “uncharacterized protein LOC419301/similar to porin” (GeneID:419301), an antiprotease and “cathepsin E-A-like/similar to nothepsin” (GeneID:417848), a protease, were the only over-expressed candidates (21-fold and 35-fold difference, respectively) that are present in the egg yolk. Additionally, we showed the 4-fold over-expression of “ovochymase-2/similar to oviductin” (GeneID:769290), a vitelline membrane-specific protease.

Conclusions

Our approach revealed that three proteases and antiproteases are likely to participate in the formation of the yolk. The role of the other 12 proteases and antiproteases which are over-expressed in our model remains unclear. At least 1/3 of proteases and antiproteases identified in egg yolk and vitelline membrane proteomes are expressed similarly in the liver regardless of the maturity of hens, and have been initially identified as regulators of haemostasis and inflammatory events. The lack of effect of sex steroids on these genes expressed in the liver but the products of which are found in the yolk suggests that these may be passively incorporated into the yolk rather than actively produced for that purpose. These results raise the question of the biological significance of egg yolk proteases and antiproteases, and more generally of all minor proteins that have been identified in egg yolk.

Participation of the 39-kDa glycoprotein (gp39) of the vitelline envelope of Bufo arenarum eggs in sperm-egg interaction

The acquisition of egg fertilizability in Bufo arenarum takes place during the oviductal transit and during this process the extracellular coelomic envelope (CE) of the eggs is converted into the vitelline envelope (VE). It has been stated that one of the necessary events leading to a fertilizable state is the proteolytic cleavage of CE glycoproteins in the oviductal pars recta by oviductin, a serine protease. Consequently, there is a marked increase in the relative quantity of glycoproteins with 39 (gp39) and 42 kDa (gp42) in the VE. In the present study, sperm-VE binding assays using heat-solubilized biotin-conjugated VE glycoproteins revealed that both gp39 and gp42 have sperm binding capacity. According to this result, our study was focused on gp39, a glycoprotein that we have previously reported as a homologue of mammalian ZPC. For this purpose, rabbit polyclonal antibodies against gp39 were generated at our laboratory. The specificity of the antibodies was confirmed with western blot of VE glycoproteins separated on SDS-PAGE. Immunohistochemical and immunoelectron studies showed gp39 distributed throughout the width of the VE. In addition, immunofluorescence assays probed that gp39 bound to the sperm head. Finally, as an approach to elucidate the possible involvement of gp39 in fertilization, inhibition assays showed that pretreatment of eggs with antibodies against gp39 generated a significant decrease in the fertilization rate. Therefore, our findings suggest that gp39, which is modified by oviductal action, participates as a VE glycoprotein ligand for sperm in Bufo arenarum fertilization.

Analysis of a sperm surface molecule that binds to a vitelline envelope component of Xenopus laevis eggs

To analyze sperm surface molecules involved in sperm-egg envelope binding in Xenopus laevis, heat-solubilized vitelline envelope (VE) dot blotted onto a polyvinylidene difluoride (PVDF) sheet was incubated with a detergent extract of sperm plasma membrane (SP-ML). The membrane components bound to the VE were detected using an antibody library against sperm plasma membrane components, and a hybridoma clone producing a monoclonal antibody (mAb) 16A2A7 was identified. This mAb was used in a Far Western blotting experiment in which VE was separated by electrophoresis, and then transferred to a PVDF strip that was incubated with SP-ML. It was found that SP-ML binds to the VE component gp37 (Xenopus homolog of mammalian ZP1). The antigens reactive to mAb 16A2A7 showed apparent molecular weights of 65-130 and 20-30 kDa, and were distributed relatively evenly over the entire sperm surface. Periodate oxidation revealed that both the pertinent epitope on the sperm surface and the ligands of VE gp37 were sugar moieties. VE gp37 was exposed on the VE surface, and the mAb 16A2A7 dose-dependently inhibited sperm binding to VE. The sperm membrane molecules reactive with mAb 16A2A7 also reacted with mAb 2A3D9, which is known to recognize the glycoprotein SGP in the sperm plasma membrane and is involved in interactions with the egg plasma membrane, indicating that the sperm membrane glycoprotein has a bifunctional role in Xenopus fertilization.

Cloning and sequence analysis of Bufo arenarum oviductin cDNA and detection of its orthologous gene expression in the mouse female reproductive tract

The glycoprotein envelope surrounding the Bufo arenarum egg exists in different functional forms. Conversion between types involves proteolysis of specific envelope glycoproteins. When the egg is released from the ovary, the envelope cannot be penetrated by sperm. Conversion to a penetrable state occurs during passage through the pars recta portion of the oviduct, where oviductin, a serine protease with trypsin-like substrate specificity, hydrolyzes two kinds of envelope glycoproteins: gp84 and gp55. The nucleotide sequence of a 3203 bp B. arenarum oviductin cDNA was obtained. Deduced amino acid sequence showed a complete open reading frame encoding 980 amino acids. B. arenarum oviductin is a multi-domain protein with a protease domain at the N-terminal region followed by two CUB domains and toward the C-terminal region another protease domain, which lacked an active histidine site, and one CUB domain. Expression of ovochymase 2, the mammalian orthologous of amphibian oviductin, was assayed in mouse female reproductive tract. Ovochymase 2 mRNA was unnoticeable in the mouse oviduct but expression was remarkable in the uterus. Phylogenetic relationship between oviductin and ovochymase 2 opens the possibility to understand the role of this enzyme in mammalian reproduction.

A serine protease in the midgut of the silkworm, Bombyx mori: protein sequencing, identification of cDNA, demonstration of its synthesis as zymogen form and activation during midgut remodeling

We identified a serine protease with a molecular mass of 37kDa in the midgut of the silkworm, Bombyx mori. The activity of this protease (37-kDa protease: p37k) appears after pupation, when the metamorphic remodeling of the midgut is under progress. The sequence analysis of the purified protease and its cDNA revealed that p37k is a trypsin-type serine protease, which is highly similar to serine proteases of other insects, including CG4386 of Drosophila melanogaster. In our molecular phylogenetic analysis, these proteases are grouped together with CG4386-like serine proteases of other insects to form an isolated cluster. The p37k protein and its putative orthologs present in this cluster have two unique sequence motifs, CxxCxC and FIDWLxxLLG, in the N-terminal side of the catalytic region. The gene for p37k is expressed in the midgut on day 2 of the silk-spinning larva, and the p37k polypeptide becomes detectable with a specific antibody at this stage of the midgut. On the other hand, p37k activity is not detectable until pupation, indicating that p37k is present in the larval midgut as an inactive precursor, which then is activated after pupation. A recombinant p37k produced using a baculovirus system is also inactive in its intact form. However, the recombinant p37k can be converted to an active protease when incubated in the homogenate of the midgut, suggesting that some unidentified midgut factor(s) are involved in the activation of p37k.

Proteomic analysis of the chicken egg vitelline membrane

The avian vitelline membrane (VM) is a multilayered proteinaceous structure separating egg white from yolk. The innermost layer of the VM, deposited onto the oocyte plasma membrane in the ovary, corresponds to the mammalian zona pellucida (ZP). The outer layer is produced in the infundibulum, the first section of the oviduct. Using high-throughput, high-end LC-MS(n) 137 proteins were identified, only 13 of which were known previously to be components of the VM. Depending on the washing protocol, two largely overlapping, but not identical, sets of identified proteins were produced from water-washed and salt-washed VMs. Most of the components of the VM were known previously from other egg compartments, such as, for instance, the egg white proteins lysozyme C, ovalbumin, ovotransferrin, and ovomucin. Specific components of the VM not identified previously in other egg compartments included eight ZP proteins, oviductin protease, and two ATPases. The vitelline outer membrane protein (VMO) VMO II was identified as beta-defensin-11. The list of VM proteins presented in this report is by far the most comprehensive dataset available at present and complements proteomic analyses of chicken egg compartments published previously.

Oviductal protease and trypsin treatment enhance sperm–envelope interaction inBufo arenarum coelomic eggs

We describe the morphological and biochemical changes in Bufo arenarum coelomic egg envelopes (CE) following passage through the oviduct. In this species, the transformation of the CE into the vitelline envelope (VE) leads to the acquisition of fertilizability and involves the cleavage of a glycoprotein component. Electrophoretic patterns indicate that a pars recta oviductal protease selectively hydrolyzes in vitro the 84 and the 55 kDa glycoproteins of the CE. During the CE to VE transformation, the relative concentrations of gp48, 42 and 39 kDa also change. In in vitro tests, sperm binding to envelope glycoprotein occurs when they are exposed to VE but not when treated with CE, and VE labeled glycoproteins bind to the head and mid piece of the sperm. The gp39 VE component has 100% identity with internal domains of the sequence deduced from ovarian cDNA for the homologous zona pellucida glycoprotein type C (ZPC) protein precursor in B. arenarum. The effects of trypsin as a substitute for oviductal protease were also examined. Trypsin selectively attacks the 84 and the 55 kDa glycoproteins without hydrolyzing other components and renders coelomic eggs fertilizable in a jelly water preparation. Therefore, trypsin can mimic in vitro the biological action of the oviductal protease. However, it does not wholly mimic the biological action of the oviduct which, in B. arenarum at least, exceeds a mere proteolytic effect. This fact was verified by the lower fertility rates and the abnormal embryo development found when trypsin-treated coelomic eggs were fertilized in vitro.

Behaviour of the vitelline envelope in Bufo arenarum oocytes matured in vitro in blockade to polyspermy

During activation of amphibian eggs, cortical granule exocytosis causes elaborate ultrastructural changes in the vitelline envelope. These changes involve modifications in the structure of the vitelline envelope and formation of a fertilization envelope (FE) that can no longer be penetrated by sperm. In Bufo arenarum, as the egg traverses the oviduct, the vitelline envelope is altered by a trypsin-like protease secreted by the oviduct, which induces an increased susceptibility of the vitelline envelope to sperm lysins. Full-grown oocytes of B. arenarum, matured in vitro by progesterone, are polyspermic, although cortical granule exocytosis seems to occur within a normal chronological sequence. These oocytes can be fertilized with or without trypsin treatment, suggesting that the vitelline envelope is totally sperm-permeable. Vitelline envelopes without trypsin treatment cannot retain either gp90 or gp96. This suggests that these glycoproteins are involved in the block to polyspermy and that trypsin treatment of matured in vitro oocytes before insemination is necessary to enable vitelline envelopes to block polyspermy. The loss of the binding capacity in vitelline envelopes isolated from B. arenarum oocytes matured in vitro with trypsin treatment and activated by electric shock suggests that previous trypsin treatment is a necessary step for sperm block to occur. When in vitro matured oocytes were incubated with the product of cortical granules obtained from in vitro matured oocytes (vCGP), vitelline envelopes with trypsin treatment were able to block sperm entry. These oocytes exhibited the characteristic signs of activation. These results support the idea that B. arenarum oocytes can be activated by external stimuli and suggest the presence of unknown oocyte surface receptors linked to the activation machinery in response to fertilization. Electrophoretic profiles obtained by SDS-PAGE of solubilized vitelline envelopes from oocytes matured in vitro revealed the conversion of gp40 (in vitro matured oocytes, without trypsin treatment) to gp38 (ascribable to trypsin activity or cortical granule product activity, CGP) and the conversion of gp70 to gp68 (ascribable to trypsin activity plus CGP activity). Taking into account that only the vitelline envelopes of in vitro matured oocytes with trypsin treatment and activated can block sperm entry, we may suggest that the conversion of gp70 to gp68 is related to the changes associated with sperm binding.

Cloning and analysis of a cDNA encoding a putative serine protease comprising two trypsin-like domains of Trichinella spiralis

The cDNA encoding a putative serine protease, TsSerP, was cloned by degenerative polymerase chain reaction and screening of the cDNA library from Trichinella spiralis adult-newborn larvae stage. Sequence analysis revealed the presence of two trypsin-like serine protease domains flanking a hydrophilic domain, with the catalytic triad residue histidine in the alpha domain substituted by an arginine residue. Southern blots indicated that this was a single copy gene in the parasite genome. Northern blots demonstrated a single 2.3-kb transcript during the muscle larvae and adult stages of T. spiralis. The recombinant protein from the TsSerP beta domain (betaSerP) was produced but not recognised by T. spiralis-infected swine serum. An anti-betaSerP polyclonal serum detected a 69-kDa polypeptide in the soluble antigens of T. spiralis muscle larvae. Immunolocalisation analysis located TsSerP on the inner layer of the cuticle and oesophagus of the parasite, suggesting a potential role in its moulting and/or digestive functions.

Uroplakin III, a novel Src substrate in Xenopus egg rafts, is a target for sperm protease essential for fertilization

In a previous study, we identified Xenopus egg uroplakin III (xUPIII), a single-transmembrane protein that localized to lipid/membrane rafts and was tyrosine-phosphorylated upon fertilization. An antibody against the xUPIII extracellular domain abolishes fertilization, suggesting that xUPIII acts not only as tyrosine kinase substrate but also as a receptor for sperm. Previously, it has been shown that the protease cathepsin B can promote a transient Ca2+ release and egg activation as seen in fertilized eggs (Mizote, A., Okamoto, S., Iwao, Y., 1999. Activation of Xenopus eggs by proteases: possible involvement of a sperm protease in fertilization. Dev. Biol. 208, 79-92). Here, we show that activation of Xenopus eggs by cathepsin B is accompanied by tyrosine phosphorylation of egg-raft-associated Src, phospholipase Cgamma, and xUPIII. Cathepsin B also promotes a partial digestion of xUPIII both in vitro and in vivo. A synthetic xUPIII-GRR peptide, which contains a potential proteolytic site, inhibits the cathepsin-B-mediated proteolysis and tyrosine phosphorylation of xUPIII and egg activation. Importantly, this peptide also inhibits sperm-induced tyrosine phosphorylation of xUPIII and egg activation. Protease activity that digests xUPIII in an xUPIII-GRR peptide-sensitive manner is present in Xenopus sperm. Several protease inhibitors, which have been identified to be inhibitory toward Xenopus fertilization, are shown to inhibit sperm-induced tyrosine phosphorylation of xUPIII. Uroplakin Ib, a tetraspanin UP member, is found to be associated with xUPIII in egg rafts. Our results highlight novel mechanisms of fertilization signaling by which xUPIII serves as a potential target for sperm protease essential for fertilization.

Binding of recombinant human proacrosin/acrosin to zona pellucida (ZP) glycoproteins. I. Studies with recombinant human ZPA, ZPB, and ZPC

OBJECTIVE

To characterize proacrosin/acrosin interaction with isolated zona pellucida (ZP) components.

DESIGN

Prospective study.

SETTING

Basic research laboratory.

PATIENT(S)

Recombinant proteins derived from human proacrosin (Rec-40, Rec-30, Rec-20, Rec-10, and Rec-6) and from human ZP glycoproteins (rec-hZPA, ZPB, and ZPC).

INTERVENTION(S)

In vitro binding assay developed to assess proacrosin/acrosin-ZP interaction.

MAIN OUTCOME MEASURE(S)

Zona pellucida glycoprotein binding to proacrosin/acrosin; estimation of binding affinity.

RESULT(S)

Of all ZP proteins, rec-hZPA demonstrated the highest binding activity toward acrosin (Rec-30) (rec-hZPB: 42% of rec-hZPA; rec-hZPC: 39% of rec-hZPA; P<.0005). Rec-hZPA interaction was disturbed by dextran sulphate (75% inhibition with 10 microM), fucose (67% inhibition with 1.5 microM), and mannose (69% inhibition with 333 mM). Comparing binding activity of proacrosin with other N-terminal acrosin fragments, Rec-40 showed 2.6-3 times higher levels. Moreover, saturable high affinity binding of Rec-40 to ZP components was observed (Kd: 34 nM for rec-hZPA, 38 nM for rec-hZPB, 63 nM for rec-hZPC).

CONCLUSION(S)

The rec-hZPA is the major ZP ligand for human proacrosin/acrosin. The interaction involves mannosyl, fucosyl, and sulfated glycans. Binding sites for rec-hZP would be located both at the N- and C-terminus of proacrosin, revealing a key role of the proenzyme in the interaction.

Comparison of the effect of mutant and wild-type p53 on global gene expression

The mechanisms for "gain-of-function" phenotypes produced by mutant p53s such as enhanced proliferation, resistance to transforming growth factor-beta-mediated growth suppression, and increased tumorigenesis are not known. One theory is that these phenotypes are caused by novel transcriptional regulatory events acquired by mutant p53s. Another explanation is that these effects are a result of an imbalance of functions caused by the retention of some of the wild-type transcriptional regulatory events in the context of a loss of other counterbalancing activities. An analysis of the ability of DNA-binding domain mutants A138P and R175H, and wild-type p53 to regulate the expression levels of 6.9 x 10(3) genes revealed that the mutants retained only <5% of the regulatory activities of the wild-type protein. A138P p53 exhibited mostly retained wild-type regulatory activities and few acquired novel events. However, R175H p53 possessed an approximately equal number of wild-type regulatory events and novel activities. This is the first report that, after examination of the regulation of a large unfocused set of genes, provides data indicating that remaining wild-type transcriptional regulatory functions existing in the absence of counterbalancing activities as well as acquired novel events both contribute to the gain-of-function phenotypes produced by mutant p53s. However, mutant p53s are likely to be distinct in terms of the extent to which each mechanism contributes to their gain-of-function phenotypes.

The sperm chemoattractant "allurin" is expressed and secreted from the Xenopus oviduct in a hormone-regulated manner

Recently, we cloned and sequenced the cDNA of allurin, a sperm chemoattractant isolated from the jelly of Xenopus laevis eggs [Proc. Natl. Acad. Sci. U.S.A. 78 (2001) 11205]. In this report, we demonstrate that allurin mRNA is expressed almost exclusively in the oviduct and that its expression is increased 2.5-fold by human chorionic gonadotropin over a 12-h period. Both dot blots and immunocytochemistry show that allurin is secreted from the upper two thirds of the oviduct that includes the pars recta and the proximal pars convoluta. Allurin appears to be deposited on the ciliated surfaces of luminal epithelial cells that come in direct contact with eggs as they move through the oviduct. Immune staining also demonstrates the presence of allurin in the serosal capsule of the oviduct. In contrast, allurin is not found within the tubular jelly-secreting glands or ducts that constitute a major portion of the oviduct wall. Therefore, we hypothesize that allurin is synthesized by nonciliated secretory cells in the luminal epithelium of the oviduct, is displayed on the ciliary layer and then mechanically mixed with jelly, and applied to eggs as they progress down the oviduct. This hypothesis is consistent with the fact that eggs progressing down the oviduct initially show evidence of allurin being incorporated into the J1 layer. Subsequently, allurin within J1 diffuses outward to J3 and eggs stored in the uterus now demonstrate a J3 localization of this chemoattractant.

Human polyserase-2, a novel enzyme with three tandem serine protease domains in a single polypeptide chain

We have cloned a human cDNA encoding a new serine protease that has been called polyserase-2 (polyserine protease-2) because it is the second identified human enzyme with several tandem serine protease domains in its amino acid sequence. The first serine protease domain contains all characteristic features of these enzymes, whereas the second and third domains lack one residue of the catalytic triad of serine proteases and are predicted to be catalytically inactive. This complex domain organization is also present in the sequences of mouse and rat polyserase-2 and resembles that of polyserase-1, which also contains three serine protease domains in its amino acid sequence. However, polyserase-2 lacks additional domains present in polyserase-1, including a type II transmembrane motif and a low-density lipoprotein receptor A module. Enzymatic analysis demonstrated that both full-length polyserase-2 and its first serine protease domain hydrolyzed synthetic peptides used for assaying serine proteases. Nevertheless, the activity of the isolated domain was greater than that of the entire protein, suggesting that the two catalytically inactive serine protease domains of polyserase-2 may modulate the activity of the first domain. Northern blot analysis showed that polyserase-2 is expressed in fetal kidney; adult skeletal muscle, liver, placenta, prostate, and heart; and tumor cell lines derived from lung and colon adenocarcinomas. Finally, analysis of post-translational processing mechanisms of polyserase-2 revealed that, contrary to those affecting to the membrane-bound polyserase-1, this novel polyprotein is a secreted enzyme whose three protease domains remain as an integral part of a single polypeptide chain.

Effects of proteinase inhibitors on fertilization in sea lamprey (Petromyzon marinus)

A search for alternative sterilants in parasitic fish encouraged us to explore the usefulness of proteinase inhibitors for this purpose. Fertilization in sea lamprey species (Petromyzon marinus L.) was inhibited by chymotrypsin and trypsin inhibitors 4'-acetamidophenyl 4-guanidinobenzoate (AGB), chymostatin, tosyl-L-lysine chloromethyl ketone (TLCK), and N-tosyl-L-phenylalanine chloromethyl ketone (TPCK) when these substances were added into a fertilization medium at the time of fertilization. Preincubation of eggs before fertilization with 100 microM TPCK, but not TLCK, resulted in inhibition of fertilization. Conversely, preincubation of spermatozoa with TLCK, but not TPCK, produced inhibition of fertilization. These data suggest the involvement of the chymotrypsin-like activity of eggs and trypsin-like activity of spermatozoa in fertilization. However, enzymes present in sperm suspensions were able to hydrolyze a chymotrypsin substrate N-glutaryl-L-phenylalanine-p-nitroanilide (GPNA) but not trypsin substrate N-alpha-benzoyl-DL-arginine-p-nitroanilide (BAPNA). The nature of this activity can be characterized as serine protease and our results indicate the involvement of serine proteinases in the fertilization of sea lamprey.

Cross-fertilization and structural comparison of egg extracellular matrix glycoproteins from Xenopus laevis and Xenopus tropicalis

While the anuran amphibian Xenopus laevis is a widely used vertebrate model system, it is not optimal for genetic manipulations due to its tetraploid genome and long generation time. A current alternative amphibian model system, Xenopus tropicalis, has the advantages of a diploid genome and a much shorter generation time. We undertook a comparative investigation of X. tropicalis egg extracellular matrix glycoproteins in relation to those already characterized in X. laevis. Fertilization methods and isolation of egg extracellular molecules were directly transferable from X. laevis to X. tropicalis. Cross-fertilizations were successful in both directions, indicating similar molecules involved in sperm-egg interactions. Egg envelopes analyzed by SDS-PAGE were found to have almost identical gel patterns, whereas jelly component profiles were similar only for the larger macromolecules (>90 kDa). The cDNA sequences for egg envelope glycoproteins ZPA, ZPB, ZPC, ZPD and ZPAX, and also egg cortical granule lectin involved in the block to polyspermy, were cloned for X. tropicalis and showed a consistent approximately 85% amino acid identity to the X. laevis sequences. Thus, homologous egg extracellular matrix molecules perform the same functions, and the molecular and cellular mechanisms of fertilization in these two species are probably equivalent.

Proteinaceous inhibitors of endo-beta-glucanases

Both plants and filamentous phytopathogens secrete proteins that inhibit endo-beta-glucanases. The first endo-beta-glucanase inhibitor proteins to be discovered are XEGIP, a tomato protein that inhibits fungal xyloglucan-specific endo-beta-1,4-glucanases, and GIP1, an oomycete protein that inhibits endo-beta-1,3-glucanases produced by the plant host. These inhibitor proteins act by forming high-affinity complexes with their endoglucanase ligands. A family of XEGIP-like proteins has been identified. At least one member of this family (extracellular dermal glycoprotein, EDGP) has been shown to have endoglucanase-inhibitor activity, while other members have sequence similarity to a xylanase inhibitor from wheat (TAXI-1). The oomycete inhibitor GIP1 is a catalytically inactive serine protease homolog (SPH) whose structure is unrelated to XEGIP. Both types of inhibitor proteins are likely to affect the interactions of plants with filamentous phytopathogens, and a basic model describing their roles in pathogenesis is proposed.

Characterization of the acrosome reaction-inducing substance in Xenopus (ARISX) secreted from the oviductal pars recta onto the vitelline envelope

We previously demonstrated that Xenopus sperm undergo an acrosome reaction on the vitelline envelope (VE) in response to the materials secreted from the oviductal pars recta [Dev. Biol. 243 (2002), 55]. A monoclonal antibody against the acrosome reaction-inducing substance in Xenopus (ARISX) was obtained by immunizing mice with pars recta extract (PRE). The acrosome reaction by PRE or on the VE was effectively inhibited by the intact anti-ARISX antibody as well as its Fab fragment, indicating that the antibody recognizes the epitopes localized on the acrosome reaction-inducing substance. On Western blots, the anti-ARISX antibody recognized a molecule with an apparent molecular mass of 300 kDa in PRE and in the VE, but this molecule was not detected in the coelomic envelope. The amount of ARISX in PRE was increased by the treatment of females with pregnant mare serum gonadotropin. Periodate oxidation of PRE completely abolished the acrosome reaction-inducing activity, indicating the involvement of the carbohydrate moieties of ARISX in inducing the acrosome reaction. On immunofluorescence observation, ARISX was localized in the epithelial cells in the posterior region of the pars recta and on the VE as fibrous structures.

Identification of the ZPC oligosaccharide ligand involved in sperm binding and the glycan structures of Xenopus laevis vitelline envelope glycoproteins

The Xenopus laevis egg vitelline envelope is composed of five glycoproteins (ZPA, ZPB, ZPC, ZPD, and ZPX). As shown previously, ZPC is the primary ligand for sperm binding to the egg envelope, and this binding involves the oligosaccharide moieties of the glycoprotein (Biol. Reprod., 62:766-774, 2000). To understand the molecular mechanism of sperm-egg envelope binding, we characterized the N-linked glycans of the vitelline envelope (VE) glycoproteins. The N-linked glycans of the VE were composed predominantly of a heterogeneous mixture of high-mannose (5-9) and neutral, complex oligosaccharides primarily derived from ZPC (the dominant glycoprotein). However, the ZPA N-linked glycans were composed of acidic-complex and high-mannose oligosaccharides, ZPX had only high-mannose oligosaccharides, and ZPB lacked N-linked oligosaccharides. The consensus sequence for N-linked glycosylation at the evolutionarily conserved residue N113 of the ZPC protein sequence was glycosylated solely with high-mannose oligosaccharides. This conserved glycosylation site may be of importance to the three-dimensional structure of the ZPC glycoproteins. One of the complex oligosaccharides of ZPC possessed terminal beta-N-acetyl-glucosamine residues. The same ZPC oligosaccharide species isolated from the activated egg envelopes lacked terminal beta-N-acetyl-glucosamine residues. We previously showed that the cortical granules contain beta-N-acetyl-glucosaminidase (J. Exp. Zool., 235:335-340, 1985). We propose that an alteration in the oligosaccharide structure of ZPC by glucosaminidase released from the cortical granule reaction is responsible for the loss of sperm binding ligand activity at fertilization.

Polyserase-I, a human polyprotease with the ability to generate independent serine protease domains from a single translation product

We have identified and cloned a human liver cDNA encoding an unusual mosaic polyprotein, called polyserase-I (polyserine protease-I). This protein exhibits a complex domain organization including a type II transmembrane motif, a low-density lipoprotein receptor A module, and three tandem serine protease domains. This unusual modular architecture is also present in the sequences predicted for mouse and rat polyserase-I. Human polyserase-I gene maps to 19p13, and its last exon overlaps with that corresponding to the 3' UTR of the gene encoding translocase of mitochondrial inner membrane 13. Northern blot analysis showed the presence of a major polyserase-I transcript of 5.4 kb in human fetal and adult tissues and in tumor cell lines. Analysis of processing mechanisms of polyserase-I revealed that it is synthesized as a membrane-associated polyprotein that is further processed to generate three independent serine protease units. Two of these domains are proteolytically active against synthetic peptides commonly used for assaying serine proteases. These proteolytic activities of the polyserase-I units are blocked by serine protease inhibitors. We show an example of generation of separate serine protease domains from a single translation product in human tissues and illustrate an additional mechanism for expanding the complexity of the human degradome, the entire protease complement of human cells and tissues.

Localization of plasminogen in the extracellular matrix of hamster eggs: exogenous activation by streptokinase

The plasminogen activator (PA)/plasminogen/plasmin proteolytic system has begun to be taken into account in the fertilization process. In this study, we demonstrated the presence of plasminogen in the extracellular matrix (ECM) of hamster oocytes by indirect immunofluorescence and immunoperoxidase assays using human anti-plasminogen. Plasminogen appeared first on the zona pellucida (ZP) of ovarian oocytes and later on the plasma membrane (PM) of oviducal eggs. This would suggest that oviducal oocytes modulate the expression of plasminogen binding sites on the PM. Human plasminogen as well as that of other species, known to be activated by streptokinase (SK), is rapidly converted to a plasmin-SK complex. We demonstrated the rapid formation of a SK-plasminogen complex that yields plasmin in the blood plasma of hamsters. Both the in vivo and in vitro SK treatment of eggs from superovulated female hamsters caused a decreased in the ZP dissolution time (ZPdt), probably either due to the proteolytic effect of plasmin or due to the SK-Plasminogen. Extracellular proteolysis assays carried out on agar-casein plates confirmed the proteolytic activity of SK-incubated eggs; the controls, on the contrary, failed to display a halo. These studies show that (1) superovulated hamster eggs contain plasminogen in their ECM, (2) oviducal eggs exhibit plasminogen on their PMs, indicating the presence of their corresponding binding sites, (3) in hamsters, SK, a non-enzymatic exogenous protein would be capable of activating ECM plasminogen to plasmin, and (4) the complex SK-plasminogen and/or the plasmin are capable of changing the ZPdt with alpha-chymotrypsin.

Acrosome reaction in sperm of the frog, Xenopus laevis: its detection and induction by oviductal pars recta secretion

Previous electron microscopic observations have shown that the acrosome of the sperm of the frog, Xenopus laevis, comprises a membrane-bounded vesicle covering the anterior-most position of the head. We obtained a sperm suspension from the testes and stained it with LysoSensor Green for observation under a confocal laser scanning microscope and found a bright fluorescence reflecting the presence of the acrosomes at the top of the sperm head in about 64% of the sperm, with no deterioration of their capacity to fertilize. About 40% of the sperm with an acrosome underwent an acrosome reaction in response to Ca(2+) ionophore A23187, as evidenced by a loss of LysoSensor Green stainability, accompanied by breakdown of the acrosomal vesicle. About 53% of the sperm bound to isolated vitelline envelopes underwent an acrosome reaction, whereas both jelly water and solubilized vitelline envelopes weakly induced an acrosome reaction. When the sperm were treated with an oviductal extract obtained from the pars recta, but not the pars convoluta region, about 40% of the sperm with acrosomes underwent an acrosome reaction. The substance containing acrosome reaction-inducing activity in the pars recta extract seemed to be a heat-unstable substance with a molecular weight of greater than 10 kDa. The activity was not inhibited by protease inhibitors but required extracellular Ca(2+) ions. These results indicate that the acrosome reaction occurs on the vitelline envelopes in response to the substance deposited from the pars recta during the passage of the oocytes through the oviduct.

Oviductin, the oviductal protease that mediates gamete interaction by affecting the vitelline coat in Bufo japonicus: its molecular cloning and analyses of expression and posttranslational activation

Previous studies indicated that the acquisition of egg fertilizability during transit through the pars recta portion of the oviduct in Bufo japonicus is accompanied by hydrolytic conversion of the vitelline coat 40- to 52-kDa components to 39-kDa components induced by a 66-kDa serine protease, "oviductin." In this study, we cloned a 3028-bp cDNA that contained an open reading frame encoding 974 amino acids with a calculated molecular mass of 107.6 kDa, including two protease domains and three repeats of CUB domains. Sequence analysis indicated that the catalytically active 66-kDa protein comprised an N-terminally located oviductin protease and two CUB domains. The oviductin gene was transcribed as a part of 6-kb mRNA that was expressed specifically in the cells lining the bottom of epithelial folds in the oviductal pars recta, and this expression was highly accelerated when the pars recta fragments were cultured in the presence of hCG. Western blot analyses using antibodies against a protease domain revealed that the catalytically inactive 102-kDa proteins in the pars recta granules yield 66-kDa catalytically active and 82- and 59-kDa inactive molecules. We propose that the oviductin translated as 107.6-kDa precursors are processed both N- and C-terminally to give rise to a 66-kDa active form comprising a serine protease and two CUB domains.

A CUB-serine protease in the olfactory organ of the spiny lobster Panulirus argus

csp, a gene encoding a protein with high sequence identity to trypsinlike serine protease and CUB domains, was identified from a cDNA library from the olfactory organ (antennular lateral flagellum) of the spiny lobster Panulirus argus. The full-length cDNA sequence of csp is 1801 bp, encoding a protein of 50.25 kD, with three domains: signal peptide, trypsinlike serine protease, and CUB (named for a class of compounds including Complement subcomponents Clr/Cls, Uegf, and Bone morphogenic protein-1). RT-PCR, Northern blots, and immunoblots showed that csp is predominantly expressed in the lateral flagellum and eyestalk. Immunocytochemistry showed that Csp is present in olfactory (aesthetasc) sensilla around auxiliary cells (glia that surround the inner dendrites of olfactory receptor neurons, ORNs) and ORN outer dendrites. We propose that Csp is expressed and secreted by auxiliary cells, associates with ORN cell membranes or extracellular matrix via the CUB domain, and has trypsinlike activity. In the eyestalk, Csp is associated with cells surrounding axons between neuropils of the eyestalk ganglia. Possible functions in the olfactory organ and eyestalk are discussed. To our knowledge, this is the first report from any olfactory system of a gene encoding a protein with serine protease and CUB domains.

A hatching enzyme substrate in the Xenopus laevis egg envelope is a high molecular weight ZPA homolog

The Xenopus laevis egg envelope is composed of six or more glycoproteins, three of which have been cloned and identified as the mammalian homologs ZPA (ZP2), ZPB (ZP1) and ZPC (ZP3). The remaining glycoproteins are a triplet of high molecular weight components that are selectively hydrolyzed by the hatching enzyme. We have isolated one of these proteins and cloned its cDNA. The mRNA for the protein was found to be expressed only in early stage oocytes, as are other envelope components. From the deduced amino acid sequence, it was indicated to be a secreted glycoprotein with a characteristic ZP domain in the C-terminal half of the molecule. The N-terminal half was unrelated to any known glycoprotein. Comparative sequence analysis of the ZP domain indicated that it was derived from an ancestor of ZPA and ZPB, with the greatest identity to ZPA. This envelope component has been designated ZPAX.

Egg envelope glycoprotein gp37 as a Xenopus homolog of mammalian ZP1, based on cDNA cloning

The egg envelope is a kind of extracellular matrix, which surrounds growing oocytes, ovulated eggs and early embryos. Among the glycoprotein components of the Xenopus laevis egg envelope, gp43/gp41 and gp69/64 have already been shown to be frog homologs of the mammalian zona pellucida components ZP3 and ZP2, respectively. To determine the structure of another major component of egg envelope, gp37, the peptides isolated from the lysyl endopeptidase digests of gp37 were sequenced for amino acids to design degenerate primers for polymerase chain reaction. By reverse transcription-polymerase chain reaction with a poly(A)+ RNA from the ovary of a postovulated female Xenopus, a specifically amplified band was obtained and sequenced. The upstream and downstream sequences of the sequenced region were completed by 5'- and 3'-rapid amplification of cDNA ends, respectively. The gp37 cDNA comprises 1674 bp and contains one open reading frame encoding a polypeptide with 543 amino acids. The predicted amino acid sequence of the gp37 cDNA has a close similarity to that of mammalian ZP1. Northern blot and in situ hybridization studies indicated that the transcript (1.8 kb) is exclusively expressed in the oocytes, particularly in the previtellogenic young oocytes, just like the expression pattern of gp43 mRNA, suggesting a coordinate transcription of the gp43 and gp37 genes in Xenopus.

Isolation and characterization of three novel serine protease genes from Xenopus laevis

Three novel cDNAs encoding serine proteases, that may play a role in early vertebrate development, have been identified from Xenopus laevis. These Xenopus cDNAs encode trypsin-like serine proteases and are designated Xenopus embryonic serine protease (Xesp)-1, Xesp-2, and XMT-SP1, a homolog of human MT-SP1. Xesp-1 is likely to be a secreted protein that functions in the extracellular space. Xesp-2 and XMP-SP1 are likely to be type II membrane proteases with multidomain structures. Xesp-2 has eight low density lipoprotein receptor (LDLR) domains and one scavenger receptor cysteine-rich (SRCR) domain, and XMT-SP1 has four LDLR domains and two CUB domains. The temporal expressions of these serine protease genes show distinct and characteristic patterns during embryogenesis, and they are differently distributed in adult tissues. Overexpression of Xesp-1 caused no significant defect in embryonic development, but overexpression of Xesp-2 or XMT-SP1 caused defective gastrulation or apoptosis, respectively. These results suggest that these proteases may play important roles during early Xenopus development, such as regulation of cell movement in gastrulae.

Independent and hetero-oligomeric-dependent sperm binding to egg envelope glycoprotein ZPC in Xenopus laevis

Vitelline envelopes are composed of glycoproteins that participate in sperm-egg interactions during the initial stages of fertilization. In Xenopus laevis, the vitelline envelope is composed of at least 4 glycoproteins (ZPA, ZPB, ZPC, and ZPX). A sperm binding assay involving the covalent coupling of envelope glycoproteins to silanized glass slides was developed. In our assay, sperm bound to the egg envelopes derived from oviposited eggs but not activated eggs. The majority of the egg envelope ligand activity for sperm binding was derived from the complex N-linked oligosaccharides of ZPC. This sperm binding involved N-acetylglucosamine and fucose residues, as binding was abolished after treatment with cortical granule beta-N-acetylglucosaminidase and commercial beta-N-acetylglucosaminidases and was reduced by 44% after treatment with alpha-fucosidase. Although both the envelope glycoproteins ZPA and ZPC possessed independent ligand activity, ZPC was the major ligand for sperm binding (75%). Mixing of isolated ZPA, ZPB, and ZPC in a ratio of 1:4:4 (equal to that in the egg envelope) resulted in sperm binding that was greater than that of the sum of the separate components. The egg glycoproteins acted in synergy to increase sperm binding. Thus, ZPC possessed both independent and hetero-oligomeric-dependent ligand activities for sperm binding.

Proteases with plasminogen activator activity in hamster oviduct

At present the physiological role of most oviductal proteins remains unknown. In this work, we present evidence that the oviductal secretion as well as the crude oviductal tissue-extract show proteolytic-like esterase and amidase activity. The proteolytic activity of the oviductal enzymes was higher in the oviducts of superovulated hamster females than in those of normal ones, indicating that gonadotrophic hormones would stimulate the synthesis and secretion of these enzymes. Some of their properties were analyzed in the 15,600-g supernatant of both oviductal tissue extracts (OE) and oviductal fluid (OF). The enzymatic activity toward the synthetic substrates p-tosyl-l-arginine methyl ester-HCl (TAME) and alpha-N-benzoyl-dl-arginine-p-nitroanilide HCl (BAPNA) was activated by calcium ions, reached a maximum at pH 7.5, and was inhibited by soybean trypsin inhibitor (SBTI), N-alpha-p-tosyl-l-lysine chloromethyl ketone HCl (TLCK), phenyl methyl sulfonyl fluoride (PMSF), and benzamidine. The OE glycoprotein fraction recognized by WGA-Sepharose affinity columns (37% total proteins) showed proteolytic activity with properties similar to the OE and OF enzymes. The protease activity could be ascribed to a plasminogen activator (PA) detected in the Triton X-100 treated tissue crude membrane fraction (Triton-CMF) and in the oviductal secretion of the superovulated females. In the Triton-CMF fraction, 100% of the proteolytic activity was plasminogen-dependent. The use of amiloride, a selective urokinase-type plasminogen activator (uPA) inhibitor, shows that 90% of this activity was due to a tissue-type plasminogen activator (tPA) and 10% to uPA whereas in the uterus 100% of the activity was tPA. Only a small percentage of the OF proteolytic activity was plasminogen-dependent, probably due to the presence of PA inhibitors in this medium.

Ovochymase, a Xenopus laevis egg extracellular protease, is translated as part of an unusual polyprotease

Ovochymase, an extracellular Xenopus laevis egg serine active-site protease with chymotrypsin-like (Phe-X) substrate specificity, is released during egg activation. Molecular cloning results revealed that ovochymase is translated as part of an unusual polyprotein proenzyme. In addition to the ovochymase protease domain at the C terminus of the deduced amino acid sequence, two unrelated serine protease domains were present, each with apparent trypsin-like (Arg/Lys-X) substrate specificity, and thus, they were designated ovotryptase1 (at the N terminus) and ovotryptase2 (a mid domain). Also, a total of five CUB domains were interspersed between the protease domains. The presence of a hydrophobic signal sequence indicated that the polyprotein was secreted. Immunolocalization and Western blot studies of all three proteases showed that they are all present in the perivitelline space of unactivated eggs, apparently as proenzymes processed away from the original polyprotein. Western blot analysis also showed that the vast majority of the proteases in ovary, eggs, and embryos were present as the proenzyme forms, suggesting that the functions of these proteases depend on very limited levels of activation.