Sperm require beta-N-acetylglucosaminidase to penetrate through the egg zona pellucida

The vertebrate- and testis- specific transmembrane protein C11ORF94 plays a critical role in sperm-oocyte membrane binding

Sperm-oocyte membrane fusion is necessary for mammalian fertilization. The factors that determine the fusion of sperm with oocytes are largely unknown. So far, spermatozoon factor IZUMO1 and the IZUMO1 counter-receptor JUNO on the oocyte membrane has been identified as a protein requiring fusion. Some sperm membrane proteins such as FIMP, SPACA6 and TEME95, have been proved not to directly regulate fusion, but their knockout will affect the fusion process of sperm and oocytes. Here, we identified a novel gene C11orf94 encoding a testicular-specific small transmembrane protein that emerges in vertebrates likely acquired via horizontal gene transfer from bacteria and plays an indispensable role in sperm-oocyte binding. We demonstrated that the deletion of C11orf94 dramatically decreased male fertility in mice. Sperm from C11orf94-deficient mice could pass through the zona pellucida, but failed to bind to the oocyte membrane, thus accumulating in the perivitelline space. In consistence, when the sperm of C11orf94-deficient mice were microinjected into the oocyte cytoplasm, fertilized oocytes were obtained and developed normally to blastocysts. Proteomics analysis revealed that C11orf94 influenced the expression of multiple gene products known to be indispensable for sperm-oocyte binding and fusion, including IZUMO1, EQTN and CRISP1. Thus, our study indicated that C11ORF94 is a vertebrate- and testis-specific small transmembrane protein that plays a critical role in sperm binding to the oolemma.

Proteomic Analysis of Intracellular and Membrane-Associated Fractions of Canine (Canis lupus familiaris) Epididymal Spermatozoa and Sperm Structure Separation

Simple Summary

Epididymal spermatozoa have great potential in current dog reproductive technologies. In the case of azoospermia or when the male dies, the recovery of epididymal spermatozoa opens new possibilities for reproduction. It is of great importance to analyze the quality of the sperm in such cases. Proteomic studies contribute to explaining the role of proteins at various stages of epididymal sperm maturation and offer potential opportunities to use them as markers of sperm quality. The present study showed, for the first time, mass spectrometry and bioinformatic analysis of intracellular and membrane-associated proteins of canine epididymal spermatozoa. Additionally, sonication was used for the separation of dog epididymal sperm morphological elements (heads, tails and acrosomes). The results revealed the presence of differentially abundant proteins in both sperm protein fractions significant for sperm function and fertilizing ability. It was also shown that these proteins participate in important sperm metabolic pathways, which may suggest their potential as sperm quality biomarkers.

Abstract

This study was provided for proteomic analysis of intracellular and membrane-associated fractions of canine (Canis lupus familiaris) epididymal spermatozoa and additionally to find optimal sonication parameters for the epididymal sperm morphological structure separation and sperm protein isolation. Sperm samples were collected from 15 dogs. Sperm protein fractions: intracellular (SIPs) and membrane-associated (SMAPs) were isolated. After sonication, sperm morphology was evaluated using Spermac Stain™. The sperm protein fractions were analyzed using gel electrophoresis (SDS-PAGE) and nanoliquid chromatography coupled to quadrupole time-of-flight mass spectrometry (NanoLC-Q-TOF/MS). UniProt database-supported identification resulted in 42 proteins identified in the SIPs and 153 proteins in the SMAPs. Differentially abundant proteins (DAPs) were found in SIPs and SMAPs. Based on a gene ontology analysis, the dominant molecular functions of SIPs were catalytic activity (50%) and binding (28%). Hydrolase activity (33%) and transferase activity (21%) functions were dominant for SMAPs. Bioinformatic analysis of SIPs and SMAPs showed their participation in important metabolic pathways in epididymal sperm, which may suggest their potential as sperm quality biomarkers. The use of sonication 150 W, 10 min, may be recommended for the separation of dog epididymal sperm heads, tails, acrosomes and the protein isolation.

Optimalisation of the Activation Medium and Effect of Inhibiting Activities of Acid Phosphatase, Lactate Dehydrogenase and β-N-Acetylglucosaminidase on the Fertilisation Success of Eurasian Perch (Perca fluviatilis L.)

Simple Summary

The purpose of this study is to determine the composition of the optimal activating solution for activating sperm motility and perch eggs, because scientific studies and reproductive procedures should be conducted in stable and repeatable conditions. We found that the best activating solution was composed of 80 mM NaCl, 20 mM KCl, 10 mM Tris, with pH 8.0 and 206 mOsm/kg. In spite of this, we also checked the influence of adding the enzyme inhibitors, such as ammonium molybdate–acid phosphatase inhibitor, gossypol – lactate dehydrogenase inhibitor and acetamide–β-N-acetylglucosaminidase inhibitor on perch sperm motility and successful perch fertilisation. We showed that the addition of acid phosphatase inhibitor in perch semen did not affect the process of fertilisation; in contrast, the addition of lactate dehydrogenase and β-N-acetylglucosaminidase inhibitors significantly decreased the percentage of perch fertilised eggs.

Abstract

Although methods for the artificial reproduction of perch have been developed, a lack of information remains regarding the enzymes present in its semen, as well as their role in the fertilisation process. In this study, we first select the optimal activating solution for perch fertilisation and then determine the inhibition effect of enzymes that have already been reported as present in the sperm of teleosts—acid phosphatase (AcP), lactic dehydrogenase (LDH) and β-N-acetylglucosaminidase (β-NAGase)—on the percentage of motile spermatozoa and fertilised eggs. Of the 8 studied activation media, a solution composed of 80 mM NaCl, 20 mM KCl, 10 mM Tris, with pH 8.0 and 206 mOsm/kg proved to be optimal for perch gametes. The addition of ammonium molybdate (AcP inhibitor) caused no significant reduction in the percentage of fertilised eggs. On the other hand, the addition of 0.25 mM gossypol (LDH inhibitor) and 0.125 M acetamide (β-N-acetylglucosaminidase inhibitor) significantly decreased the fertilisation percentage to 41.1% and 52.4%, respectively, in contrast to the control (89.9 %). Both LDH and β-NAGase thus seem to play a very important role in the perch fertilisation process.

Proteome of cat semen obtained after urethral catheterization

The binding of seminal plasma (SP) proteins by spermatozoa plays an important role in the regulation of sperm epididymal maturation, motility gaining in female reproductive tracts and sperm-egg interaction. The aim of the study was to analyze the SP and sperm extracts proteome of cat (Felis catus) semen. The seminal plasma and spermatozoa were obtained by urethra catheterization from 10 male cats. Proteins were extracted using RIPA buffer and separated by electrophoresis (SDS-PAGE). The gels were analyzed using MultiAnalyst software. The proteins were subsequently analyzed using NanoUPLC-Q-TOF/MS. UniProt database-supported identification resulted in 106 proteins identified in the cat SP and 98 proteins in the extracts of spermatozoa. Based on a gene ontology analysis, dominant molecular functions of feline SP proteins were binding, catalytic, and antioxidant activity (56%, 33%, and 11% of cases, respectively). The molecular functions of sperm extracts proteins were mainly involved in catalytic activity (41%) and binding (23%). The proteins present in both, the SP and spermatozoa's extracts, were: serum albumin (ALB), semenogelin 2 (SEMG 2), clusterin (CLU), lactoferrin (LTF), prostatic acid phosphatase (ACPP), prolactin inducible protein (PIP), negative elongation factor E (NELF-E) and ectonucleotide pyrophosphatase (ENPP3). Protein-protein interactions analysis showed significant connection for 12 proteins in the cat semen. The seminal plasma proteins which, with high probability score, participate in important metabolic pathways are: glutathione peroxidases (GPx5 and 6), prostatic acid phosphatase (ACPP), β-hexosaminidase (HEXB), polymeric immunoglobulin receptor (pIgR) and serpin family F member 1 (SERPINF1). For sperm protein extracts it were: pyruvate dehydrogenase (PDHB), succinate-CoA-ligase (SUCLA2), malate dehydrogenase (MDH2), ATP synthase F1 subunit alpha (ATP5F1A) and tubulin beta (TUBB).

Alterations in oxidative responses and post-translational modification caused by p,p´-DDE in Mus spretus testes reveal Cys oxidation status in proteins related to cell-redox homeostasis and male fertility

The major derivate of DDT, 1,1-dichloro-2,2-bis (p-chlorophenyl) ethylene (p,p´-DDE), is a persistent pollutant previously associated with oxidative stress. Additionally, p,p´-DDE has been linked to several metabolic alterations related to sexual function in rodents. In this study, we analysed the effects of a non-lethal p,p´-DDE dose to Mus spretus mice in testes, focusing on oxidative damage to biomolecules, defence mechanisms against oxidative stress and post-translational protein modifications. No increase in lipid or DNA oxidation was observed, although antioxidative enzymatic defences and redox status of glutathione were altered in several ways. Global protein carbonylation and phosphorylation were significantly reduced in testes from p,p´-DDE-exposed mice; however, the total redox state of Cys thiols did not exhibit a defined pattern. We analysed the reversible redox state of specific Cys residues in detail with differential isotopic labelling and a shotgun labelling-based MS/MS proteomic approach for identification and quantification of altered peptides. Our results show that Cys residues are significantly affected by p,p´-DDE in several proteins related to oxidative stress and/or male fertility, particularly those participating in fertilization, sperm capacitation and blood coagulation. These molecular changes could explain the sexual abnormalities previously described in p,p´-DDE exposed organisms.

A mechanism-based GlcNAc-inspired cyclophellitol inactivator of the peptidoglycan recycling enzyme NagZ reverses resistance to β-lactams in Pseudomonas aeruginosa

The development of a potent mechanism-based inactivator of NagZ, an enzyme critical to the production of inducible AmpC β-lactamase in Gram-negative bacteria, is presented. This inactivator significantly reduces MIC values for important β-lactams against a clinically relevant strain of Pseudomonas aeruginosa.

Cryopreservation and egg yolk medium alter the proteome of ram spermatozoa

Cryopreservation causes significant lethal and sub-lethal damage to spermatozoa. In order to improve freezing outcomes, a comprehensive understanding of sub-lethal damage is required. Cryopreservation induced changes to sperm proteins have been investigated in several species, but few have employed currently available state of the art, data independent acquisition mass spectrometry (MS) methods. We used the SWATH LC-MS method to quantitatively profile proteomic changes to ram spermatozoa following exposure to egg yolk and cryopreservation. Egg yolk contributed 15 proteins to spermatozoa, including vitellogenins, apolipoproteins and complement component C3. Cryopreservation significantly altered the abundance of 51 proteins. Overall, 27 proteins increased (e.g. SERPINB1, FER) and 24 proteins decreased (e.g. CCT subunits, CSNK1G2, TOM1L1) in frozen thawed ram spermatozoa, compared to fresh spermatozoa. Chaperones constituted 20% of the proteins lost from spermatozoa following cryopreservation. These alterations may interfere with both normal cellular functioning and the ability of frozen thawed spermatozoa to appropriately respond to stress. This is the first study to apply SWATH mass spectrometry techniques to characterise proteins contributed by egg yolk based freezing media and to profile cryopreservation induced proteomic changes to ram spermatozoa.

SIGNIFICANCE

This study profiles changes to the sperm proteome induced by exposure to egg yolk based media and the process of cryopreservation, and the biological consequences are discussed.

Glycopolymer induction of mouse sperm acrosomal exocytosis shows highly cooperative self-antagonism

Identifying inducers of sperm acrosomal exocytosis (AE) to understand sperm functionality is important for both mechanistic and clinical studies in mammalian fertilization. Epifluorescence microscopy methods, while reproducible, are laborious and incompatible for high throughput screening. Flow cytometry methods are ideal for quantitative measurements on large numbers of samples, yet typically rely on the use of lectins that can interfere with physiologic AE-inducers. Here, we present an optimized triple stain flow cytometric method that is suitable for high-throughput screening of AE activation by glycopolymers. SYTO-17 and propidium iodide (PI) were used to differentiate cells based on their membrane integrity or viability, and membrane impermeable soybean trypsin inhibitor (SBTI) was used to monitor acrosome exocytosis. The SBTI/PI/SYTO-17 combination provides a positive screen for viability and AE of live sperm cells with minimal noise or false positives. A scattering gate enables the use of samples that may be contaminated with non-cellular aggregates, e.g., cryopreservation agents. This assay format enabled detailed analysis of glycopolymer dose response curves. We found that fucose polymer has a narrow effective dose range (EC50 = 1.6 μM; IC50 = 13.5 μM); whereas mannose polymer and β-N-acetylglucosamine polymer have broader effective dose ranges (EC50 = 1.2 μM and 3.4 μM, respectively). These results highlight the importance of testing inducers over a large concentration range in small increments for accurate comparison.

The activity of three glycosidases (β-Ν-acetyloglucosaminidase, α-mannosidase, and β-galactosidase) in the follicular fluid and in the maturation medium affects bovine oocyte maturation

We studied the role of follicular fluid's (FF) glycosidase (α-mannosidase [α-ΜΑΝ], β-Ν-acetyloglucosaminidase [NAGASE], β-galactosidase [β-GAL]) activity during IVM of bovine oocytes. Oocytes were allocated into two groups according to the follicular size (small follicle [SF]: 2-5 mm, large follicle [LF]: >5-8 mm). In experiment 1, cumulus-oocyte complexes (COCs) quality was evaluated according to morphologic criteria (grades A, B-C, D); oocyte (n = 801) nuclear maturation was assessed after 24 hours of incubation. Bovine embryos were produced in vitro in groups (experiment 2, n = 1503 oocytes) or individually (experiment 3, n = 50 oocytes). More grade-A and -BC COCs were collected from SF and LF groups, respectively (P < 0.05). Maturation rate (experiment 1) and cleavage rate (experiments 2 and 3) were similar in SF and LF groups. Activity of all glycosidases in FF was higher (P < 0.05) in SF group than in LF group, whereas in maturation medium of SF group it was, overall, significantly lower than in that of LF (experiments 2 and 3). In FF of SF group, NAGASE positively associated with grade-A oocytes and negatively with BC oocytes; increased β-GAL was associated with degenerated oocytes. Cleavage rate in LF group, related negatively to NAGASE and positively to α-MAN in maturation medium. These results indicate that during maturation, COCs release NAGASE and consume β-GAL, but differences probably exist between individual and group maturation.

Identification and characterization of a bovine sperm acrosomal matrix protein and its mechanism of interaction with acrosomal hydrolases

Fertilization, the union of male and female gametes to create offspring, is an intricate biological process dependent upon several biochemical and physiological events. Our understanding of the functions of protein constituents of the outer acrosomal membrane-associated matrix complex (OMC) is limited. A highly purified OMC fraction isolated from bovine cauda sperm heads comprised 54, 50, 45, and 38-19 kDa polypeptides. The objective of this study is to identify and characterize the 45 kDa (OMC45) polypeptide, to define its role in binding acrosomal hydrolases, and to examine the fate of OMC45 polypeptide during the acrosome reaction. We isolated OMC45 polypeptide from the high-pH insoluble fraction of OMC. Proteomic analysis of OMC45 by MALDI-TOF-TOF yielded eight peptides that matched the NCBI database sequence of Tektin 3 (TEKT3). Triton X-100-permeabilized cauda sperm exhibited intense staining of the acrosomal segment with anti-OMC45 and anti-TEKT3. The OMC45 polypeptide was solubilized by radio-immunoprecipitation assay buffer extraction. The solubilized fraction was subjected to immunoprecipitation analysis. The OMC45 polypeptide was recovered in the anti-OMC45 immunoprecipitation pellet. An identical blot stained with anti-TEKT3 exhibited the presence of TEKT3 polypeptide in the anti-OMC45 pellet. Our immunofluorescence and biochemical studies confirm the proteomics identification of OMC45 polypeptide and that it exhibits a sequence similarity to TEKT3. OMC45 glycoprotein possesses both N-linked and O-linked oligosaccharides. Deglycosylated OMC45 revealed a significant reduction in both acrosin and N-acetylglucosaminidase (NAGA) binding in comparison with acrosin and NAGA binding to a native OMC45 polypeptide, demonstrating the important role of oligosaccharides in hydrolase binding. OMC45 polypeptide is not released during the acrosome reaction but remains in the particulate cell subfraction, associated with the hybrid membrane complex.

Mutations in four glycosyl hydrolases reveal a highly coordinated pathway for rhodopsin biosynthesis and N-glycan trimming in Drosophila melanogaster

As newly synthesized glycoproteins move through the secretory pathway, the asparagine-linked glycan (N-glycan) undergoes extensive modifications involving the sequential removal and addition of sugar residues. These modifications are critical for the proper assembly, quality control and transport of glycoproteins during biosynthesis. The importance of N-glycosylation is illustrated by a growing list of diseases that result from defects in the biosynthesis and processing of N-linked glycans. The major rhodopsin in Drosophila melanogaster photoreceptors, Rh1, is highly unique among glycoproteins, as the N-glycan appears to be completely removed during Rh1 biosynthesis and maturation. However, much of the deglycosylation pathway for Rh1 remains unknown. To elucidate the key steps in Rh1 deglycosylation in vivo, we characterized mutant alleles of four Drosophila glycosyl hydrolases, namely α-mannosidase-II (α-Man-II), α-mannosidase-IIb (α-Man-IIb), a β-N-acetylglucosaminidase called fused lobes (Fdl), and hexosaminidase 1 (Hexo1). We have demonstrated that these four enzymes play essential and unique roles in a highly coordinated pathway for oligosaccharide trimming during Rh1 biosynthesis. Our results reveal that α-Man-II and α-Man-IIb are not isozymes like their mammalian counterparts, but rather function at distinct stages in Rh1 maturation. Also of significance, our results indicate that Hexo1 has a biosynthetic role in N-glycan processing during Rh1 maturation. This is unexpected given that in humans, the hexosaminidases are typically lysosomal enzymes involved in N-glycan catabolism with no known roles in protein biosynthesis. Here, we present a genetic dissection of glycoprotein processing in Drosophila and unveil key steps in N-glycan trimming during Rh1 biosynthesis. Taken together, our results provide fundamental advances towards understanding the complex and highly regulated pathway of N-glycosylation in vivo and reveal novel insights into the functions of glycosyl hydrolases in the secretory pathway.

Functional O-GlcNAc modifications: implications in molecular regulation and pathophysiology

O-linked β-N-acetylglucosamine (O-GlcNAc) is a regulatory post-translational modification of intracellular proteins. The dynamic and inducible cycling of the modification is governed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA) in response to UDP-GlcNAc levels in the hexosamine biosynthetic pathway (HBP). Due to its reliance on glucose flux and substrate availability, a major focus in the field has been on how O-GlcNAc contributes to metabolic disease. For years this post-translational modification has been known to modify thousands of proteins implicated in various disorders, but direct functional connections have until recently remained elusive. New research is beginning to reveal the specific mechanisms through which O-GlcNAc influences cell dynamics and disease pathology including clear examples of O-GlcNAc modification at a specific site on a given protein altering its biological functions. The following review intends to focus primarily on studies in the last half decade linking O-GlcNAc modification of proteins with chromatin-directed gene regulation, developmental processes, and several metabolically related disorders including Alzheimer's, heart disease and cancer. These studies illustrate the emerging importance of this post-translational modification in biological processes and multiple pathophysiologies.

Fucose, mannose, and β-N-acetylglucosamine glycopolymers initiate the mouse sperm acrosome reaction through convergent signaling pathways

The sperm acrosome reaction (AR), an essential exocytosis step in mammalian fertilization, is mediated by a species-specific interaction of sperm surface molecules with glycans on the egg. Previous studies indicate that a subset of terminal carbohydrates on the mouse egg zona pellucida (ZP) trigger the AR by cross-linking or aggregating receptors on the sperm membrane. However, the exact role of those carbohydrates in AR has not been identified and the mechanism underlying the AR still needs further investigation. To study this process, a series of glycopolymers was synthesized. The glycopolymers are composed of a multivalent scaffold (norbornene), a functional ligand (previously identified ZP terminal monosaccharides), and a linker connecting the ligand and the scaffold. The polymers were tested for their ability to initiate AR and through which signaling pathways AR induction occurred. Our data demonstrate that mannose, fucose, and β-N-acetylglucosamine 10-mers and 100-mers initiate AR in a dose-dependent manner, and the 100-mers are more potent on a per monomer basis than the 10-mers. Although nearly equipotent in inducing the AR at the optimal concentrations, their AR activation kinetics are not identical. Similar to mouse ZP3, all 100-mer-activated AR are sensitive to guanine-binding regulatory proteins (G-proteins), tyrosine kinase, protein kinase A, protein kinase C, and Ca²⁺-related antagonists. Thus, the chemotypes of synthetic glycopolymers imitate the physiologic AR-activation agents and provide evidence that occupation of one of at least three different receptor binding sites is sufficient to initiate the AR.

The development of selective inhibitors of NagZ: increased susceptibility of Gram-negative bacteria to β-lactams

The increasing incidence of inducible chromosomal AmpC β-lactamases within the clinic is a growing concern because these enzymes deactivate a broad range of even the most recently developed β-lactam antibiotics. As a result, new strategies are needed to block the action of this antibiotic resistance enzyme. Presented here is a strategy to combat the action of inducible AmpC by inhibiting the β-glucosaminidase NagZ, which is an enzyme involved in regulating the induction of AmpC expression. A divergent route facilitating the rapid synthesis of a series of N-acyl analogues of 2-acetamido-2-deoxynojirimycin is reported here. Among these compounds are potent NagZ inhibitors that are selective against functionally related human enzymes. These compounds reduce minimum inhibitory concentration values for β-lactams against a clinically relevant Gram-negative bacterium bearing inducible chromosomal AmpC β-lactamase, Pseudomonas aeruginosa. The structure of a NagZ–inhibitor complex provides insight into the molecular basis for inhibition by these compounds.

Modes of acrosin functioning during fertilization

Mammalian fertilization is a complex process that involves gamete recognition, penetration, and fusion. Biochemical studies that identified the role of acrosome components during sperm-ova interaction especially the zona pellucida (ZP) provided major advances in sperm cell biology. Acrosin (a typical serine protease) functions during fertilization in several significant ways which include: a) activation of acrosome components, b) secondary binding with the ZP, and c) hydrolysis of the ZP. However, studies using knockout (KO) acrosin-deficient mice cast doubt on the traditional role of acrosin in fertilization. The KO acrosin-deficient mice exhibit normal fecundity except for delayed fertilization. Despite the doubt cast on the traditional role of acrosin by the KO acrosin-deficient mouse studies, acrosin still remains a major protease involved in multiple processes of fertilization. In this review, we assess the functional profile of acrosin and briefly summarize recent findings on proteases involved in fertilization. We propose a refined scheme for the functional role of acrosin in fertilization. We particularly emphasize the role of acrosin in acrosome exocytosis and activation of other acrosome components based on advanced technology like structural X-ray analysis.

Involvement of A1Adenosine Receptors in the Acquisition of Fertilizing Capacity

Ejaculated mammalian spermatozoa acquire competence to fertilize oocytes by a two-step process: capacitation followed by acrosome reaction. The biochemical and biophysical modifications occurring in vivo in the female reproductive tract can be reproduced in vitro, and previous studies have suggested a capacitative role for adenosine A(1) receptor (A(1)R). Mice with a targeted disruption of the Adora 1 gene (A(1)R-/- mice) provide a useful model for better understanding the role of the A(1)R in fertility. Murine spermatozoa express A(1)R in the head, neck, midpiece region, and tail. The number of capacitated spermatozoa incubated in human tubal fluid was significantly reduced in A(1)R-/- compared with A(1)R+/+ and A(1)R+/- spermatozoa. The difference between A(1) R+/+ and A(1)R-/- mouse spermatozoa was mainly in the time necessary to reach the maximum percentage of capacitation. A(1)R+/+ murine sperm obtained the full state of capacitation within 90 minutes whereas A(1)R-/- sperm required 240 minutes. Caffeine, a known antagonist of A(1) and A(2A) adenosine receptors, lowered the number of capacitated sperm and affected the time of capacitation in a dose-dependent manner, mimicking the effects of the lack of A(1) receptors. Although number, motility, and viability of A(1)R-/- murine sperm was not significantly different from A(1)R+/+ mouse spermatozoa, a significant reduction of the number of pups produced by A(1)R-/- male mice suggests that A(1) receptors must be fully operative to accomplish the optimal degree of capacitation and thereby fertilization.

β-hexosaminidase from Xenopus laevis eggs and oocytes: from gene to immunochemical characterization

Glycosidases are present both in sperm and eggs in vertebrates and have been associated with different fertilization steps as gamete binding, egg coat penetration, and polyspermy prevention. In this manuscript, we have analyzed the activity of different glycosidases of Xenopus laevis eggs. The main activity corresponded to N-acetyl-β-D-glucosaminidase (Hex), which was reported to participate both in gamete binding and polyspermy prevention among phylogenetically distant animals. We have raised homologous antibodies against a recombinant N-terminal fragment of a X. laevis Hex, and characterized egg's Hex both by Western blot and immunohistochemical assays. Noteworthy, Hex was mainly localized to the cortex of animal hemisphere of full-grown oocytes and oviposited eggs, and remained unaltered after fertilization. Hex is constituted by different pair arrangements of two subunits (α and β), giving rise to three possible Hex isoforms: A (αβ), B (ββ), and S (αα). However, no information was available regarding molecular identity of Hex in amphibians. We present for the first time the primary sequences of two isoforms of X. laevis Hex. Interestingly, our results suggest that α- and β-like subunits that constitute Hex isoforms could be synthesized from a same gene in Xenopus, by alternative exon use. This finding denotes an evolutionary divergence with mammals, where α and β Hex subunits are synthesized from different genes on different chromosomes.

Isolation and proteomic characterization of the mouse sperm acrosomal matrix

A critical step during fertilization is the sperm acrosome reaction in which the acrosome releases its contents allowing the spermatozoa to penetrate the egg investments. The sperm acrosomal contents are composed of both soluble material and an insoluble material called the acrosomal matrix (AM). The AM is thought to provide a stable structure from which associated proteins are differentially released during fertilization. Because of its important role during fertilization, efforts have been put toward isolating the AM for biochemical study and to date AM have been isolated from hamster, guinea pig, and bull spermatozoa. However, attempts to isolate AM from mouse spermatozoa, the species in which fertilization is well-studied, have been unsuccessful possibly because of the small size of the mouse sperm acrosome and/or its fusiform shape. Herein we describe a procedure for the isolation of the AM from caput and cauda mouse epididymal spermatozoa. We further carried out a proteomic analysis of the isolated AM from both sperm populations and identified 501 new proteins previously not detected by proteomics in mouse spermatozoa. A comparison of the AM proteome from caput and cauda spermatozoa showed that the AM undergoes maturational changes during epididymal transit similar to other sperm domains. Together, our studies suggest the AM to be a dynamic and functional structure carrying out a variety of biological processes as implied by the presence of a diverse group of proteins including proteases, chaperones, hydrolases, transporters, enzyme modulators, transferases, cytoskeletal proteins, and others.

Two distinct Ca(2+) signaling pathways modulate sperm flagellar beating patterns in mice

Hyperactivation, a swimming pattern of mammalian sperm in the oviduct, is essential for fertilization. It is characterized by asymmetrical flagellar beating and an increase of cytoplasmic Ca(2+). We observed that some mouse sperm swimming in the oviduct produce high-amplitude pro-hook bends (bends in the direction of the hook on the head), whereas other sperm produce high-amplitude anti-hook bends. Switching direction of the major bends could serve to redirect sperm toward oocytes. We hypothesized that different Ca(2+) signaling pathways produce high-amplitude pro-hook and anti-hook bends. In vitro, sperm that hyperactivated during capacitation (because of activation of CATSPER plasma membrane Ca(2+) channels) developed high-amplitude pro-hook bends. The CATSPER activators procaine and 4-aminopyridine (4-AP) also induced high-amplitude pro-hook bends. Thimerosal, which triggers a Ca(2+) release from internal stores, induced high-amplitude anti-hook bends. Activation of CATSPER channels is facilitated by a pH rise, so both Ca(2+) and pH responses to treatments with 4-AP and thimerosal were monitored. Thimerosal triggered a Ca(2+) increase that initiated at the base of the flagellum, whereas 4-AP initiated a rise in the proximal principal piece. Only 4-AP triggered a flagellar pH rise. Proteins were extracted from sperm for examination of phosphorylation patterns induced by Ca(2+) signaling. Procaine and 4-AP induced phosphorylation of proteins on threonine and serine, whereas thimerosal primarily induced dephosphorylation of proteins. Tyrosine phosphorylation was unaffected. We concluded that hyperactivation, which is associated with capacitation, can be modulated by release of Ca(2+) from intracellular stores to reverse the direction of the dominant flagellar bend and, thus, redirect sperm.

Chemical arsenal for the study of O-GlcNAc

The concepts of both protein glycosylation and cellular signaling have been influenced by O-linked-β-N-acetylglucosamine (O-GlcNAc) modification (O-GlcNAcylation) on the hydroxyl group of serine or threonine residues. Unlike conventional protein glycosylation, O-GlcNAcylation is localized in the nucleocytoplasm and its cycling is a dynamic process that operates in a highly regulated manner in response to various cellular stimuli. These characteristics render O-GlcNAcylation similar to phosphorylation, which has long been considered a major regulatory mechanism in cellular processes. Various efficient chemical approaches and novel mass spectrometric (MS) techniques have uncovered numerous O-GlcNAcylated proteins that are involved in the regulation of many important cellular events. These discoveries imply that O-GlcNAcylation is another major regulator of cellular signaling. However, in contrast to phosphorylation, which is regulated by hundreds of kinases and phosphatases, dynamic O-GlcNAc cycling is catalyzed by only two enzymes: uridine diphospho-N-acetyl-glucosamine:polypeptide β-N-acetylglucosaminyl transferase (OGT) and β-D-N-acetylglucosaminidase (OGA). Many useful chemical tools have recently been used to greatly expand our understanding of the extensive crosstalk between O-GlcNAcylation and phosphorylation and hence of cellular signaling. This review article describes the various useful chemical tools that have been developed and discusses the considerable advances made in the O-GlcNAc field.

Inhibition of a bacterial O-GlcNAcase homologue by lactone and lactam derivatives: structural, kinetic and thermodynamic analyses

The dynamic, intracellular, O-GlcNAc modification is of continuing interest and one whose study through targeted "chemical genetics" approaches is set to increase. Of particular importance is the inhibition of the O-GlcNAc hydrolase, O-GlcNAcase (OGA), since this provides a route to elevate cellular O-GlcNAc levels, and subsequent phenotypic evaluation. Such a small molecule approach complements other methods and potentially avoids changes in protein-protein interactions that manifest themselves in molecular biological approaches to O-GlcNAc transferase knockout or over-expression. Here we describe the kinetic, thermodynamic and three-dimensional structural analysis of a bacterial OGA analogue from Bacteroides thetaiotaomicron, BtGH84, in complex with a lactone oxime (LOGNAc) and a lactam form of N-acetylglucosamine and compare their binding signatures with that of the more potent inhibitor O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino N-phenyl carbamate (PUGNAc). We show that both LOGNAc and the N-acetyl gluconolactam are significantly poorer inhibitors than PUGNAc, which may reflect poorer mimicry of transition state geometry and steric clashes with the enzyme upon binding; drawbacks that the phenyl carbamate adornment of PUGNAc helps mitigate. Implications for the design of future generations of inhibitors are discussed.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 2: changes in spermatid organelles associated with development of spermatozoa

Spermiogenesis is a long process whereby haploid spermatids derived from the meiotic divisions of spermatocytes undergo metamorphosis into spermatozoa. It is subdivided into distinct steps with 19 being identified in rats, 16 in mouse and 8 in humans. Spermiogenesis extends over 22.7 days in rats and 21.6 days in humans. In this part, we review several key events that take place during the development of spermatids from a structural and functional point of view. During early spermiogenesis, the Golgi apparatus forms the acrosome, a lysosome-like membrane bound organelle involved in fertilization. The endoplasmic reticulum undergoes several topographical and structural modifications including the formation of the radial body and annulate lamellae. The chromatoid body is fully developed and undergoes structural and functional modifications at this time. It is suspected to be involved in RNA storing and processing. The shape of the spermatid head undergoes extensive structural changes that are species-specific, and the nuclear chromatin becomes compacted to accommodate the stream-lined appearance of the sperm head. Microtubules become organized to form a curtain or manchette that associates with spermatids at specific steps of their development. It is involved in maintenance of the sperm head shape and trafficking of proteins in the spermatid cytoplasm. During spermiogenesis, many genes/proteins have been implicated in the diverse dynamic events occurring at this time of development of germ cells and the absence of some of these have been shown to result in subfertility or infertility.

A model of the acrosome reaction progression via the acrosomal membrane-anchored protein equatorin

It is important to establish a reliable and progressive model of the acrosome reaction. Here, we present a progression model of the acrosome reaction centering around the acrosomal membrane-anchored protein equatorin (MN9), comparing the staining pattern traced by MN9 antibody immunofluorescence with that traced by Arachis hypogaea agglutinin (PNA)–FITC. Prior to the acrosome reaction, equatorin was present in both the anterior acrosome and the equatorial segment. Since sperm on zona pellucida showed various staining patterns, MN9-immunostaining patterns were classified into four stages: initial, early, advanced, and final. As the acrosome reaction progressed from the initial to the early stage, equatorin spread from the peripheral region of the anterior acrosome toward the center of the equatorial segment, gradually over the entire region of the equatorial segment during the advanced stage, and finally uniformly at the equatorial segment at the final stage. In contrast, the PNA–FITC signals spread more quickly from the peripheral region of the acrosome toward the entire equatorial segment, while decreasing in staining intensity, and finally became weak at the final stage. MN9-immunogold electron microscopy showed equatorin on the hybrid vesicles surrounded by amorphous substances at advanced stage of acrosome reaction. Equatorin decreased in molecular mass from 40–60 to 35 kDa, and the signal intensity of 35 kDa equatorin increased as the acrosome reaction progressed. Thus, the established equatorin-based progression model will be useful for analyzing not only the behavior of equatorin but also of other molecules of interest involved in the acrosome reaction.

Regulation of Dauer formation by O-GlcNAcylation in Caenorhabditis elegans

Modification of proteins at serine or threonine residues with N-acetylglucosamine, termed O-GlcNAcylation, plays an important role in most eukaryotic cells. To understand the molecular mechanism by which O-GlcNAcylation regulates the entry of Caenorhabditis elegans into the non-aging dauer state, we performed proteomic studies using two mutant strains: the O-GlcNAc transferase-deficient ogt-1(ok430) strain and the O-GlcNAcase-defective oga-1(ok1207) strain. In the presence of the dauer pheromone daumone, ogt-1 showed suppression of dauer formation, whereas oga-1 exhibited enhancement of dauer formation. Consistent with these findings, treatment of wild-type N2 worms with low concentrations of daumone and the O-GlcNAcase inhibitor O-(2-acetamido-2-deoxy-d-glucopyranosylidene)amino-N-phenylcarbamate (PUGNAc) enhanced dauer formation, which was dependent on intact O-GlcNAcylation metabolism. We also found that the treatment of daumone enhanced O-GlcNAcylation in vivo. Seven proteins, identified by coupled two-dimensional electrophoresis/liquid chromatography-mass spectroscopy (LC-MS) analysis, were differentially expressed in oga-1(ok1207) worms compared with wild-type N2 worms. The identities of these proteins suggest that O- GlcNAcylation influences stress resistance, protein folding, and mitochondrial function. Using O-GlcNAc labeling with fluorescent dye combined with two-dimensional electrophoresis/LC-MS analysis, we also identified five proteins that were differentially O-GlcNAcylated during dauer formation. Analysis of these candidate O-GlcNAcylated proteins suggests that O-GlcNAcylation may regulate cytoskeleton modifications and protein turnover during dauer formation.

Sperm-zona pellucida interaction: molecular mechanisms and the potential for contraceptive intervention

At the moment of insemination, millions of mammalian sperm cells are released into the female reproductive tract with the single goal of finding the oocyte. The spermatozoa subsequently ignore the thousands of cells they make contact with during their journey to the site of fertilization, until they reach the surface of the oocyte. At this point, they bind tenaciously to the acellular coat, known as the zona pellucida, which surrounds the oocyte and orchestrate a cascade of cellular interactions that culminate in fertilization. These exquisitely cell- and species- specific recognition events are among the most strategically important cellular interactions in biology. Understanding the cellular and molecular mechanisms that underpin them has implications for the etiology of human infertility and the development of novel targets for fertility regulation. Herein we describe our current understanding of the molecular basis of successful sperm-zona pellucida binding.

Zonadhesin D3-polypeptides vary among species but are similar in Equus species capable of interbreeding

Zonadhesin is a rapidly evolving protein in the sperm acrosome that confers species specificity to sperm-zona pellucida adhesion. Though structural variation in zonadhesin likely contributes to its species-specific function, the protein has not previously been characterized in organisms capable of interbreeding. Here we compared properties of zonadhesin in several animals, including the horse (Equus caballus), donkey (E. asinus), and Grevy's zebra (E. grevyi) to determine if variation in zonadhesin correlates with ability of gametes to cross-fertilize. Zonadhesin localized to the apical acrosomes of spermatozoa from all three Equus species, similar to its localization in other animals. Likewise, in horse and donkey testis, zonadhesin was detected only in germ cells, first in the acrosomal granule of round spermatids and then in the developing acrosomes of elongating spermatids. Among non-Equus species, D3-domain polypeptides of mature, processed zonadhesin varied markedly in size and detergent solubility. However, zonadhesin D3-domain polypeptides in horse, donkey, and zebra spermatozoa exhibited identical electrophoretic mobility and detergent solubility. Equus zonadhesin D3-polypeptides (p110/p80 doublet) were most similar in size to porcine and bovine zonadhesin D3-polypeptides (p105). Sequence comparisons revealed that the horse zonadhesin precursor's domain content and arrangement are similar to those of zonadhesin from other large animals. Partial sequences of horse and donkey zonadhesin were much more similar to each other (>99% identity) than they were to orthologous sequences of human, pig, rabbit, and mouse zonadhesin (52%-72% identity). We conclude that conservation of zonadhesin D3-polypeptide properties correlates with ability of Equus species to interbreed.

Increasing O-GlcNAc levels: An overview of small-molecule inhibitors of O-GlcNAcase

The O-GlcNAc modification is found on many nucleocytoplasmic proteins. The dynamic nature of O-GlcNAc, which in some ways is reminiscent of phosphorylation, has enabled investigators to modulate the stoichiometry of O-GlcNAc on proteins in order to study its function. Although several genetic and pharmacological methods for manipulating O-GlcNAc levels have been described, one of the most direct approaches of increasing global O-GlcNAc levels is by using small-molecule inhibitors of O-GlcNAcase (OGA). As the interest in increasing O-GlcNAc levels has grown, so too has the number of OGA inhibitors. This review provides an overview of the available methods of increasing O-GlcNAc levels, with a special emphasis on inhibition of OGA by small molecules. Known inhibitors of OGA are discussed with particular attention on those most suitable for cell-based biological studies. Several examples in which OGA inhibitors have been used to study the functional role of the O-GlcNAc modification in biological systems are discussed, highlighting the pros and cons of different inhibitors.

FLUOROMETRIC STUDY OF RABBIT SPERM HEAD MEMBRANE PHOSPHOLIPID ASYMMETRY DURING CAPACITATION AND ACROSOME REACTION USING ANNEXIN-V FITC

This study was conducted to evaluate phosphatidylserine translocation in head plasma membrane of Percoll-gradient purified of rabbit cauda epididymal sperm during capacitation and acrosome reaction (AR) using Annexin-V. Propidium iodide was used as control to reject dead or dying cells. The presence and distribution of Annexin-V binding sites were analyzed using flow fluorocytometry and confocal microscopy. After 6 h of incubation of sperm in capacitation medium, the number of cells positively stained with Annexin-V showed a small but significant increment. The Annexin-V binding sites produced during capacitation were found mainly in the post-acrosomal region of the sperm head plasma membrane. After AR induction with progesterone, the localization of phosphatidylserine was changed and the Annexin-V binding sites were found almost only in the acrosomal region, but with higher number of binding sites in the equatorial area. On the contrary, after AR induction with A23187, phosphatidylserine translocation, although predominant over the acrosomal region, was also observed in the post-acrosomal region. Plasma membrane destabilization during capacitation and AR may be important for sperm-oocyte fusion.

Disruption of ADAM3 impairs the migration of sperm into oviduct in mouse

Sperm from four different gene-disrupted mouse lines (calmegin [Clgn], Adam1a, Adam2, and Ace) are known to have defective zona-binding ability. Moreover, it is also reported that the sperm from all of these mouse lines exhibit another common phenotype of impaired migration into oviduct despite the large number of sperm found in uterus after coitus. On the other hand, the sperm from the Adam3-disrupted mouse line was reported to have defects in binding ability to zona, but were able to move into the oviduct. In order to clarify the difference, we investigated the migration of ADAM3-null sperm into oviduct precisely by visualizing the sperm by using acrosin-green fluorescent protein as a tag. As a result, in contrast to previous observations, it was demonstrated that the Adam3-disrupted sperm were unable to migrate into the oviduct after coitus. It was ultimately shown that, in five out of five different gene-disrupted mouse lines, the phenotype of impaired sperm binding to zona pellucida was accompanied by the loss of ability of sperm to migrate into the oviduct. This indicates a close relationship between the two phenomena, and also that sperm migration into the oviduct is a crucial step for fertilization.

Glycosidase determination in bovine oviducal fluid at the follicular and luteal phases of the oestrous cycle

Gamete recognition and binding of spermatozoa to the oviduct are carbohydrate-mediated processes in which several glycosidases are thought to have a role, although this has not been demonstrated unequivocally. Oviducal fluid is the biological milieu in which fertilisation and early embryo development take place, but the enzyme composition of oviducal fluid is largely unknown. The aim of the present study was to determine glycosidase activity and protein content in bovine oviducal fluid (bOF) and the volume of fluid collected per oviduct. Oviducts obtained from a slaughterhouse were classified as either in the follicular or luteal phase on the basis of ovarian luteal morphology. Oviducal fluid was aspirated, centrifuged and the volume determined. Samples were then frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen for the activity of seven glycosidases at pH 7.2. The results indicate that bOF has alpha-l-fucosidase, beta-N-acetyl-glucosaminidase, beta-d-galactosidase, alpha-D-mannosidase and beta-N-acetyl-galactosaminidase activity during both phases of the cycle, with the specific activity of the latter two enzymes being higher during the follicular phase. There was no N-acetyl-neuraminidase or alpha-d-galactosidase activity detected in bOF at either phase of the oestrous cycle at pH 7.2, but activity for both glycosidases was detected at pH 4.4. There were no differences in protein concentration or the volume of bOF collected between the two phases of the cycle. These findings indicate that oviducal fluid exhibits glycosidase activity, with specific variations throughout the oestrous cycle, suggesting that these enzymes play a role in carbohydrate-mediated events.

Determination of glycosidase activity in porcine oviductal fluid at the different phases of the estrous cycle

Sperm-oocyte binding and gamete-oviductal epithelium interactions are carbohydrate-mediated events occurring in the oviductal fluid (OF). Thus, knowledge about the activities of glycosidases (enzymes catalyzing hydrolytic cleavage of terminal sugar residues) in this milieu would help us understand the molecular mechanisms involved in these events. This work was carried out to investigate the glycosidase activity, protein content, and volume of OF collected from gilts and sows. Oviducts were classified into four phases of the estrous cycle (early follicular, late follicular, early luteal, and late luteal) based on the appearance of the ovaries. OF was aspirated, centrifuged, measured for volume, and frozen until assay. Substrates conjugated to 4-methylumbelliferyl were used to screen the activities of seven different glycosidases at physiological pH (7.2). alpha-L-Fucosidase and beta-N-acetyl-glucosaminidase activities increased at the late follicular phase to decrease after ovulation. beta-D-Galactosidase, alpha-D-mannosidase, and beta-N-acetyl-galactosaminidase showed higher activities at the early follicular phase, which decreased after ovulation. N-Acetyl-neuraminidase and alpha-D-galactosidase did not show activity at any phase of estrous cycle neither in sows nor in gilts at pH 7.2, although it did at acidic pH (4.4) in the follicular and luteal phase samples. Total protein also changed during the cycle showing the maximum secretion at the late follicular phase (2118.6+/-200.7 microg/oviduct). The highest volumes of OF were collected from the oviducts at the late follicular phase (50.7+/-1.3 microl/oviduct). These results indicate that OF from sows and gilts shows glycosidase activity varying throughout the estrous cycle suggesting a role of these enzymes in carbohydrate-mediated events.

The molecular evolution of acrosin in placental mammals

Acrosin is thought to fulfill several different roles in fertilization including that of a serine protease and in secondary zona pellucida (ZP) binding. However, acrosin's importance as a fertilization protein has been questioned. Especially since it was discovered that acrosin knockout mice are fertile. In this study, we explored the sites involved in serine protease activity and secondary binding. We also assessed conservation in functional sites across species and examined whether amino acid changes present in the human population have the potential to affect fertility. In addition, since many mammalian reproduction proteins have been found to evolve rapidly, we tested for positive selection. Sequences from 43 mammals from all 19 placental orders, which included a total of 828 nucleotides from acrosin exons 2, 3, 4, and a portion of exon 5, were obtained. We found that all sites of the serine catalytic triad as well as three other sites linked to catalytic activity were completely conserved. Five of six sites proposed to play a role in secondary binding were 100% conserved as basic residues. These results support an evolutionary conserved role for acrosin as a serine protease and secondary binding protein across placental mammals. We found statistically significant support for positive selection within acrosin, but no single amino acid site reached the significance level of P > 0.95 for inclusion within the category omega > 1. Based upon two amino acid mutation scoring systems, three out of seven human residue changing single nucleotide polymorphisms (SNPs) were found to be potentially protein-altering mutations.

Recombinant mouse sperm ZP3-binding protein (ZP3R/sp56) forms a high order oligomer that binds eggs and inhibits mouse fertilization in vitro

Many candidates have been proposed as zona pellucida-binding proteins. Without precluding a role for any of those candidates, we focused on mouse sperm protein ZP3R/sp56, which is localized in the acrosomal matrix. The objective of this study was to analyze the role of ZP3R/sp56 in mouse fertilization. We expressed recombinant ZP3R/sp56 as a secreted protein in HEK293 cells and purified it from serum-free, conditioned medium. In the presence of reducing agents, the recombinant ZP3R/sp56 exhibited a molecular weight similar to that observed for the native ZP3R/sp56. Reminiscent of the native protein, recombinant ZP3R/sp56 formed a high molecular weight, disulfide cross-linked oligomer consisting of six or more monomers under non-reducing conditions. Recombinant ZP3R/sp56 bound to the zona pellucida of unfertilized eggs but not to 2-cell embryos, indicating that the changes that take place in the zona pellucida at fertilization affected the interaction of this protein with the zona pellucida. The extent of in vitro fertilization was reduced in a dose-dependent manner when unfertilized eggs were preincubated with recombinant ZP3R/sp56 (74% drop at the maximum concentrations assayed). Eggs incubated with the recombinant protein showed an absence of or very few sperm in the perivitelline space, suggesting that the reduction in the fertilization rate is caused by the inhibition of sperm binding and/or penetration through the zona pellucida. These results indicate that sperm ZP3R/sp56 is important for sperm-zona interactions during fertilization and support the concept that the acrosomal matrix plays an essential role in mediating the binding of sperm to the zona pellucida.

Small Molecule Inhibitors of a Glycoside Hydrolase Attenuate Inducible AmpC-mediated β-Lactam Resistance

The increasing spread of plasmid-borne ampC-ampR operons is of considerable medical importance, since the AmpC beta-lactamases they encode confer high level resistance to many third generation cephalosporins. Induction of AmpC beta-lactamase from endogenous or plasmid-borne ampC-ampR operons is mediated by a catabolic inducer molecule, 1,6-anhydro-N-acetylmuramic acid (MurNAc) tripeptide, an intermediate of the cell wall recycling pathway derived from the peptidoglycan. Here we describe a strategy for attenuating the antibiotic resistance associated with the ampC-ampR operon by blocking the formation of the inducer molecule using small molecule inhibitors of NagZ, the glycoside hydrolase catalyzing the formation of this inducer molecule. The structure of the NagZ-inhibitor complex provides insight into the molecular basis for inhibition and enables the development of inhibitors with 100-fold selectivity for NagZ over functionally related human enzymes. These PUGNAc-derived inhibitors reduce the minimal inhibitory concentration (MIC) values for several clinically relevant cephalosporins in both wild-type and AmpC-hyperproducing strains lacking functional AmpD.

Characterization of human sperm N-acetylglucosaminidase

N-acetylglucosaminidase (NAG) is particularly active in mammalian spermatozoa and appears to be involved in fertilization. Although it is assumed that this enzyme is acrosomal, previous results from our laboratory suggest the presence of NAG at the sperm plasma membrane level. The present study attempted to analyse the subcellular distribution of this enzyme in human spermatozoa. Sperm were incubated under different conditions and NAG activity measured in the soluble extracts and cell pellets using a specific fluorometric substrate. A significant proportion of NAG activity was released when sperm were incubated in culture medium, suggesting a weak association with the plasma membrane. This location was confirmed by western blot analysis of plasma membrane fractions and immunofluorescence on non-permeabilized sperm, which showed a positive signal mainly on the acrosomal domain. The distribution of NAG activity between plasma membrane and acrosome was analysed after cell disruption by freezing and thawing. Triton X-100 stimulated sperm and epididymal NAG activity but not the enzyme obtained from other sources. In addition, biotinylated human recombinant NAG was able to bind to human sperm. Finally, after sperm incubation under capacitating conditions, NAG total activity increased and the sperm enzyme lost its ability to be stimulated by Triton X-100. The possible connection of these results with sperm maturation, capacitation and NAG participation in primary binding to the zona pellucida, was discussed.

Effect of culture-medium supplementation with α-mannosidase and/or β-N-acetyloglucosaminidase on in vitro bovine embryonic development

Glycosidases are enzymes with a potential role in embryonic development. The objectives of this study were to assess: (a) whether in vitro bovine embryonic development is affected by the addition of beta-N-acetyloglucosaminidase (beta-NAGASE) and/or alpha-mannosidase to the culture medium and (b) whether these enzymes are utilized by bovine embryos during their development in vitro. Bovine embryos were produced using standard methods of IVM, IVF and IVC. Presumptive zygotes were cultured in groups of 20 in 50 microl drops of SOF medium (plus 5% FBS after 24 h culture) incubated in 5% CO2, 5% O2 and 90% N2 at 38.5 degrees C. The groups of zygotes were allocated to four treatments in which the culture medium was supplemented with: (1) beta-NAGASE, (2) alpha-mannosidase, (3) beta-NAGASE plus alpha-mannosidase, and (4) control (no supplement). Embryos were evaluated and samples of culture medium collected and frozen prior to assay for glycosidases at day 7 of culture. The experimental design was a randomised block arrangement of 4 treatments x 7 replicates with 20 zygotes per plot (culture droplet). Data were analysed by ANOVA and presented as mean +/- S.E.M. The osmolarity of the control culture medium was 272 mOsm. This was increased to 279 mOsm by the addition of alpha-mannosidase, 424 mOsm by beta-NAGASE and 337 mOsm with a combination of the two enzymes. The beta-NAGASE supplemented medium and the combined supplement reduced (0%) the development of zygotes to morula or blastocyst stages (P < 0.002) relative to control medium (35.7 +/- 8.4%). Embryo development was also reduced to 21.9 +/- 3.2 (P< 0.002), relative to control, by alpha-mannosidase supplementation. The reduced embryo development in the beta-NAGASE-supplemented medium was attributed to increased osmolarity of the culture medium. Embryos appeared to utilize alpha-mannosidase because its concentration decreased from 600.95 +/- 174.03 IU/l in drops without zygotes/embryos to 211.01 +/- 71.59 IU/l in drops with zygotes/embryos. Other culture media supplementation showed no significant differences between droplets, with or without zygotes/embryos. It was concluded that beta-NAGASE increased medium osmolarity, embryos utilized alpha-mannosidase and both glycosidases (singly or in combination) inhibited the development of bovine zygotes to morulae/blastocysts.

Impairment of adult male reproductive function in rats exposed to ethanol since puberty

The objective of this work was to evaluate reproductive function in adult male rats exposed to ethanol since puberty. Male Wistar rats, 50 days old, received a liquid diet with 36% of the daily calories derived from ethanol or an isocaloric control diet for 55 days. The ethanol treatment impaired sexual behavior and only 22% of these rats reached ejaculation. The fertility of ethanol-treated animals was significantly reduced, mainly after natural mating. Serum testosterone levels, daily sperm production and sperm count in the epididymis were also significantly diminished after ethanol treatment, associated with an acceleration of the sperm transit time in the cauda epididymidis, decrease in sperm motility and increased percentage of abnormal shaped sperm cells. The results showed that chronic consumption of ethanol beginning at puberty impairs the reproductive function of adult male rats.

Sperm chromatin remodeling after intracytoplasmic sperm injection differs from that of in vitro fertilization

Intracytoplasmic sperm injection (ICSI) is a popular method used in assisted conception, and live offspring have been born from a variety of species, including humans. In ICSI, sperm chromatin is introduced into the oocyte together with the acrosome, a structure that does not enter the oocyte during normal fertilization. We compared sperm chromatin remodeling, the potential of embryos to develop in vitro, and DNA synthesis in mouse embryos obtained from in vitro fertilization (IVF) and ICSI. We also tested whether sperm pretreatment prior to ICSI (i.e., capacitation, acrosome reaction, membrane removal, and reduction of disulfide bonds in protamines) facilitates chromatin remodeling and affects embryo development. Sperm chromatin was examined on air-dried, Giemsa-stained preparations at 30-min intervals for up to 4.5 h postfertilization. In all experimental groups, the oocytes underwent activation and formed pronuclei with similar rates. However, the dynamics of sperm chromatin remodeling in ICSI and IVF embryos varied. In ICSI, chromatin remodeling was more asynchronous than in IVF. Sperm capacitation prior to injection enhanced remodeling asynchrony and resulted in delayed pronuclei formation and DNA synthesis. The removal of the acrosome prior to injection with calcium ionophore A23187 but not with detergent Triton X-100 allowed more synchronous chromatin remodeling, timely DNA synthesis, and good embryo development. Our data have significance for the refinement of the molecular and biologic mechanisms associated with ICSI for current and future applications.

A divergent synthesis of 2-acyl derivatives of PUGNAc yields selective inhibitors of O-GlcNAcase

A divergent route facilitating the rapid synthesis of a series of O-(2-acetamido-2-deoxy-D-glucopyranosylidene)amino N-phenylcarbamate (PUGNAc)-based inhibitors, bearing different N-acyl groups has been developed. All compounds of this series are inhibitors of both human O-GlcNAcase and human beta-hexosaminidase, yet some effectively exploit differences between the active site architectures of these two human enzymes which render them selective for O-GlcNAcase. Such inhibitors may be valuable tools in dissecting the role of the O-GlcNAc post-translational modification at the cellular and organismal level since these compounds may have different pharmacokinetic properties when compared to other inhibitors of beta-N-acetyl-glucosaminidases.

Thermodynamic study of beta-N-acetylhexosaminidase enzyme heterogeneity in human seminal plasma

BACKGROUND

It has been suggested that the activity of beta-N-acetylhexosaminidase (Hex) in seminal plasma may be used as a biochemical marker of azoospermia. The purpose of our study was to evaluate this hypothesis using a thermodynamic procedure developed to determine total Hex activity and that of its isoenzymes in this biological fluid.

METHODS

Using the substrate 3,3'-dichlorophenolsulphoftaleinil N-acetyl-beta-D-glucosaminide, a highly significant difference (p<0.001) is found between the activation energy of Hex A (41.5 kJ/mol) and of Hex B (72.3 kJ/mol), making it possible to determine the activity of these isoenzymes from the apparent activation energy of the total Hex in seminal plasma.

RESULTS

A significant difference between the normozoospermic and azoospermic groups was only found for Hex A isoenzyme activity (p<0.05), although with considerable overlapping between the values of both groups. Significant partial correlations were found for the total Hex, Hex A and Hex B activities with the immobile spermatozoa count (p<0.01) and for total Hex and Hex B with the dead spermatozoa count (p<0.05). In turn, Hex A had a significant partial correlation with the live spermatozoa count (p<0.05); however, Hex activity in seminal plasma of acromosomal origin appears to be of little importance in quantitative terms.

CONCLUSIONS

It was not possible to confirm that total Hex activity in seminal plasma, or even of its isoenzymes Hex A and Hex B, is a suitable biochemical marker of azoospermia (efficiency< or =67%). The thermodynamic procedure described may be a useful alternative for the study of the Hex enzyme heterogeneity in spermatozoa.