Differential release of guinea pig sperm acrosomal components during exocytosis

IZUMO1 Receptor Localization during Hyaluronic Acid Selection in Human Spermatozoa

IZUMO1 is an acrosome transmembrane protein implicated in the adhesion and fusion of gametes. This study aims to describe the distribution of IZUMO1 in human sperm under different physiological conditions: before capacitation (NCS), at one-hour capacitation (CS1), after a hyaluronic acid (HA) selection test (mature, MS1 and immature, IS1), and induced acrosome reaction from one-hour-capacitated sperm (ARS1). The data obtained in NCS, CS1, and MS1 significantly highlight dotted fluorescence in the acrosomal region (P1) as the major staining pattern (~70%). Moreover, we describe a new distribution pattern (P2) with a dotted acrosomal region and a labelled equatorial region that significantly increases in HA-bound spermatozoa, suggesting the onset of the migration of IZUMO1. In contrast, unbound spermatozoa presented an increase in P3 (equatorial region labelled) and P4 (not labelled). Finally, costaining to observe IZUMO1 distribution and acrosome status was performed in ARS1. Interestingly, we reported a variety of combinations between the IZUMO1 staining patterns and the acrosomal stages. In conclusion, these data show as a novelty the diffusion of the IZUMO1 protein during different physiological conditions that could contribute to the improvement in sperm selection techniques.

Guinea Pig Sperm Morphology and Fertility under Different Photoperiod

Sperm morphology can predict the reproductive male fertilizing potential. This study aimed to determine the morphological and morphometric spermatozoa characteristics from guinea pigs subjected to different photoperiodic stimulation. Thirty F1 guinea pigs were randomly assigned to three photoperiodic treatments: FT1 (photoperiod with 10 Light/14 Dark LED light), FT2 (photoperiod with 10L/14D sunlight), and FT0 (room without direct light source). At 107 ± 9.8 days of age, sperm concentration and motility were higher in the FT0 and FT1 groups (p < 0.05); furthermore, there were no differences in nucleus length and ellipticity between the FT0 and FT1 groups, but the sperm of the FT1 group was higher in perimeter and nuclear area, while that of the FT0 group was higher in roughness, regularity, midpiece length, and tail (p < 0.01). Expanding acrosome (Type 2) was more frequent in the FT2 group, but there was variation in head measurements between all morphological categories. Pregnancy rate, calving age, and mating age were higher in the FT0 group; meanwhile, the FT1 group initiated successful matings earlier (p < 0.01). The FT0 group had a higher fertility rate, and the age of mating and first calving were earlier in the FT1 group than the FT0 group, but no pregnancies were reported for the FT2 group. Photoperiodic stimulation can increase the morphometric dimensions of guinea pig spermatozoa, favoring the reproductive characteristics, but sunlight could reduce their size due to heat stress.

Sperm selection by the oviduct: perspectives for male fertility and assisted reproductive technologies†

The contribution of sperm to embryogenesis is gaining attention with up to 50% of infertility cases being attributed to a paternal factor. The traditional methods used in assisted reproductive technologies for selecting and assessing sperm quality are mainly based on motility and viability parameters. However, other sperm characteristics, including deoxyribonucleic acid integrity, have major consequences for successful live birth. In natural reproduction, sperm navigate the male and female reproductive tract to reach and fertilize the egg. During transport, sperm encounter many obstacles that dramatically reduce the number arriving at the fertilization site. In humans, the number of sperm is reduced from tens of millions in the ejaculate to hundreds in the Fallopian tube (oviduct). Whether this sperm population has higher fertilization potential is not fully understood, but several studies in animals indicate that many defective sperm do not advance to the site of fertilization. Moreover, the oviduct plays a key role in fertility by modulating sperm transport, viability, and maturation, providing sperm that are ready to fertilize at the appropriate time. Here we present evidence of sperm selection by the oviduct with emphasis on the mechanisms of selection and the sperm characteristics selected. Considering the sperm parameters that are essential for healthy embryonic development, we discuss the use of novel in vitro sperm selection methods that mimic physiological conditions. We propose that insight gained from understanding how the oviduct selects sperm can be translated to assisted reproductive technologies to yield high fertilization, embryonic development, and pregnancy rates.

Membrane Remodeling and Matrix Dispersal Intermediates During Mammalian Acrosomal Exocytosis

To become fertilization-competent, mammalian sperm must undergo a complex series of biochemical and morphological changes in the female reproductive tract. These changes, collectively called capacitation, culminate in the exocytosis of the acrosome, a large vesicle overlying the nucleus. Acrosomal exocytosis is not an all-or-nothing event but rather a regulated process in which vesicle cargo disperses gradually. However, the structural mechanisms underlying this controlled release remain undefined. In addition, unlike other exocytotic events, fusing membranes are shed as vesicles; the cell thus loses the entire anterior two-thirds of its plasma membrane and yet remains intact, while the remaining nonvesiculated plasma membrane becomes fusogenic. Precisely how cell integrity is maintained throughout this drastic vesiculation process is unclear, as is how it ultimately leads to the acquisition of fusion competence. Here, we use cryoelectron tomography to visualize these processes in unfixed, unstained, fully hydrated sperm. We show that paracrystalline structures within the acrosome disassemble during capacitation and acrosomal exocytosis, representing a plausible mechanism for gradual dispersal of the acrosomal matrix. We find that the architecture of the sperm head supports an atypical membrane fission-fusion pathway that maintains cell integrity. Finally, we detail how the acrosome reaction transforms both the micron-scale topography and the nanoscale protein landscape of the sperm surface, thus priming the sperm for fertilization.

Different Approaches to Record Human Sperm Exocytosis

Acrosome reaction is an exocytic process that enables a sperm to penetrate the zona pellucida and fertilize an egg. The process involves the fenestration and vesiculation of the sperm plasma membrane and outer acrosomal membrane, releasing the acrosomal content. Given the importance of the acrosome secretion in fertilization, many different methods have been developed to detect the acrosome reaction of sperm. In this chapter, we describe detailed practical procedures to assess the acrosomal status of human spermatozoa. To do this, we resorted to light optical and epifluorescence microscopy, flow cytometry, and transmission electron microscopy. We also itemize the protocol for real-time measurements of the acrosome reaction by confocal microscopy. Further, we discuss the level of complexity, costs, and the reasons why a researcher should choose each technique.This chapter is designed to provide the user with sufficient background to measure acrosomal exocytosis in human sperm.

Ligands and Receptors Involved in the Sperm-Zona Pellucida Interactions in Mammals

Sperm-zona pellucida (ZP) interaction, involving the binding of sperm surface ligands to complementary carbohydrates of ZP, is the first direct gamete contact event crucial for subsequent gamete fusion and successful fertilization in mammals. It is a complex process mediated by the coordinated engagement of multiple ZP receptors forming high-molecular-weight (HMW) protein complexes at the acrosomal region of the sperm surface. The present article aims to review the current understanding of sperm-ZP binding in the four most studied mammalian models, i.e., murine, porcine, bovine, and human, and summarizes the candidate ZP receptors with established ZP affinity, including their origins and the mechanisms of ZP binding. Further, it compares and contrasts the ZP structure and carbohydrate composition in the aforementioned model organisms. The comprehensive understanding of sperm-ZP interaction mechanisms is critical for the diagnosis of infertility and thus becomes an integral part of assisted reproductive therapies/technologies.

Effect of Photoperiod with Sunlight at Thermal Stress and Sperm Parameters in Guinea Pigs

&lt;b&gt;Background and Objective:&lt;/b&gt; Photoperiod can regulate reproductive physiological processes in mammals, in which improvements in testosterone concentration, testicular volume and seminal quality have been reported. The aim was to evaluate the influence of photoperiod treatments on guinea pigs' spermatic parameters. &lt;b&gt;Materials and Methods:&lt;/b&gt; Thirty guinea pigs, between males and females, were distributed in two rooms with the photoperiodic treatment of 10 hrs light and 14 hrs dark (PT&lt;sub&gt;1&lt;/sub&gt; with artificial photoperiod and PT&lt;sub&gt;2&lt;/sub&gt; photoperiod with sunlight by opening windows from 08:00-18:00) and one without any direct light stimulus (PT&lt;sub&gt;0&lt;/sub&gt;) for 78 days. The temperature and humidity were recorded and the TH index was calculated for each room. The sperms were recovered in Tris base medium from the epididymis of 16 males to determine sperm concentration, motility, kinetic parameters, vitality, HOST, acrosomal integrity and DNA fragmentation. &lt;b&gt;Results:&lt;/b&gt; Sperm values in PT&lt;sub&gt;1&lt;/sub&gt; and PT&lt;sub&gt;0&lt;/sub&gt; were similar but PT&lt;sub&gt;2&lt;/sub&gt; obtained values lower in sperm concentration, non-progressive motility, total motility, VCL, ALH, vitality, HOST+, acrosomal integrity, sperm with non-fragmented DNA and no pregnancies were reported (0/5). A 100% pregnancy was observed in PT&lt;sub&gt;0&lt;/sub&gt; (4/4) and 50% in PT&lt;sub&gt;1&lt;/sub&gt; (2/4). However, precocity was evidenced in PT&lt;sub&gt;1&lt;/sub&gt; compared to PT&lt;sub&gt;0&lt;/sub&gt;. PT&lt;sub&gt;2&lt;/sub&gt; recorded higher peaks in temperature (33.8°C, THI 81, considered as thermal stress) compared to PT&lt;sub&gt;0&lt;/sub&gt; (32.65°C, THI 81.8) and PT&lt;sub&gt;1&lt;/sub&gt; (32.75°C, THI 81.6). &lt;b&gt;Conclusion:&lt;/b&gt; An artificial photoperiod can improve sperm characteristics and reproductive precociousness of guinea pigs, unlike the photoperiod with sunlight, which generated low spermiogram values and absence of pregnancy due to thermal stress.

CRISP2 Is a Regulator of Multiple Aspects of Sperm Function and Male Fertility

The cysteine-rich secretory proteins (CRISPs) are a group of proteins that show a pronounced expression biased to the male reproductive tract. Although sperm encounter CRISPs at virtually all phases of sperm development and maturation, CRISP2 is the sole CRISP produced during spermatogenesis, wherein it is incorporated into the developing sperm head and tail. In this study we tested the necessity for CRISP2 in male fertility using Crisp2 loss-of-function mouse models. In doing so, we revealed a role for CRISP2 in establishing the ability of sperm to undergo the acrosome reaction and in establishing a normal flagellum waveform. Crisp2-deficient sperm possess a stiff midpiece and are thus unable to manifest the rapid form of progressive motility seen in wild type sperm. As a consequence, Crisp2-deficient males are subfertile. Furthermore, a yeast two-hybrid screen and immunoprecipitation studies reveal that CRISP2 can bind to the CATSPER1 subunit of the Catsper ion channel, which is necessary for normal sperm motility. Collectively, these data define CRISP2 as a determinant of male fertility and explain previous clinical associations between human CRISP2 expression and fertility.

Peanut agglutinin specifically binds to a sperm region between the nucleus and mitochondria in tunicates and sea urchins

Peanut agglutinin (PNA) is an established marker of the mammalian acrosome. However, we observed that PNA specifically binds to a unique intracellular structure alongside the nucleus in ascidian sperm. Here, we characterize the PNA-binding structure in sperm of marine invertebrates. PNA bound to the region between the mitochondrion and nucleus in spermatozoa of ascidians, sea urchins, and an appendicularian. However, PNA-binding substances were not exposed by the calcium ionophore ionomycin in three ascidian species, indicating that it is a distinct structure from the acrosome. Instead, the ascidian PNA-binding region was shed with the mitochondrion from the sperm head via an ionomycin-induced sperm reaction. The ascidian PNA-binding substance appeared to be solubilized with SDS, but not Triton X-100, describing its detergent resistance. Lectins, PHA-L₄ , SSA, and MAL-I were detected at an area similar to the PNA-binding region, suggesting that it contains a variety of glycans. The location and some of the components of the PNA-binding region were similar to known endoplasmic reticulum (ER)-derived structures, although the ER marker concanavalin A accumulated at an area adjacent to but not overlapping the PNA-binding region. Therefore, we conclude that ascidian sperm possess a non-acrosomal, Triton-resistant, glycan-rich intracellular structure that may play a general role in reproduction of tunicates and sea urchins given its presence across a wide taxonomic range.

The Molecules of Sperm Exocytosis

Exocytosis is a fundamental process used by eukaryotic cells to release biological compounds and to insert lipids and proteins in the plasma membrane. Specialized secretory cells undergo regulated exocytosis in response to physiological signals. Sperm exocytosis or acrosome reaction (AR) is essentially a regulated secretion with special characteristics. We will focus here on some of these unique features, covering the topology, kinetics, and molecular mechanisms that prepare, drive, and regulate membrane fusion during the AR. Last, we will compare acrosomal release with exocytosis in other model systems.

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.

Mechanisms of fertilization elucidated by gene-manipulated animals

Capacitation and the acrosome reaction are key phenomena in mammalian fertilization. These phenomena were found more than 60 years ago. However, fundamental questions regarding the nature of capacitation and the timing of the acrosome reaction remain unsolved. Factors were postulated over time, but as their roles were not verified by gene-disruption experiments, widely accepted notions concerning the mechanism of fertilization are facing modifications. Today, although in vitro fertilization systems remain our central research tool, the importance of in vivo observations must be revisited. Here, primarily focusing on our own research, I summarize how in vivo observations using gene-manipulated animals have elucidated new concepts in the mechanisms of fertilization.

Fertilization defects in sperm from Cysteine-rich secretory protein 2 (Crisp2) knockout mice: implications for fertility disorders

STUDY HYPOTHESIS

We hypothesize that fertility disorders in patients with aberrant expression of Cysteine-RIch Secretory Protein 2 (CRISP2) could be linked to the proposed functional role of this protein in fertilization.

STUDY FINDING

Our in vivo and in vitro observations reveal that Crisp2-knockout mice exhibit significant defects in fertility-associated parameters under demanding conditions, as well as deficiencies in sperm fertilizing ability, hyperactivation development and intracellular Ca(2+) regulation.

WHAT IS KNOWN ALREADY

Testicular CRISP2 is present in mature sperm and has been proposed to participate in gamete fusion in both humans and rodents. Interestingly, evidence in humans shows that aberrant expression of CRISP2 is associated with male infertility.

STUDY DESIGN, SAMPLES/MATERIALS, METHODS

A mouse line carrying a deletion in the sixth exon of the Crisp2 gene was generated. The analyses of the reproductive phenotype of Crisp2(-/-) adult males included the evaluation of their fertility before and after being subjected to unilateral vasectomy, in vivo fertilization rates obtained after mating with either estrus or superovulated females, in vitro sperm fertilizing ability and different sperm functional parameters associated with capacitation such as tyrosine phosphorylation (by western blot), acrosome reaction (by Coomassie Blue staining), hyperactivation (by computer-assisted sperm analysis) and intracellular Ca(2+) levels (by flow cytometry).

MAIN RESULTS AND THE ROLE OF CHANCE

Crisp2(-/-) males presented normal fertility and in vivo fertilization rates when mated with estrus females. However, the mutant mice showed clear defects in those reproductive parameters compared with controls under more demanding conditions, i.e. when subjected to unilateral vasectomy to reduce the number of ejaculated sperm (n = 5; P< 0.05), or when mated with hormone-treated females containing a high number of eggs in the ampulla (n ≥ 5; P< 0.01). In vitro fertilization studies revealed that Crisp2(-/-) sperm exhibited deficiencies to penetrate the egg vestments (i.e. cumulus oophorus and zona pellucida) and to fuse with the egg (n ≥ 6; P< 0.01). Consistent with this, Crisp2-null sperm showed lower levels of hyperactivation (n = 7; P< 0.05), a vigorous motility required for penetration of the egg coats, as well as a dysregulation in intracellular Ca(2+) levels associated with capacitation (n = 5; P< 0.001).

LIMITATIONS, REASONS FOR CAUTION

The analysis of the possible mechanisms involved in fertility disorders in men with abnormal expression of CRISP2 was carried out in Crisp2 knockout mice due to the ethical and technical problems inherent to the use of human gametes for fertilization studies.

WIDER IMPLICATIONS OF THE FINDINGS

Our findings in mice showing that Crisp2(-/-) males exhibit fertility and fertilization defects under demanding conditions support fertilization defects in sperm as a mechanism underlying infertility in men with aberrant expression of CRISP2. Moreover, our observations in mice resemble the situation in humans where fertility disorders can or cannot be detected depending on the accumulation of own individual defects or the fertility status of the partner. Finally, the fact that reproductive defects in mice are masked by conventional mating highlights the need of using different experimental approaches to analyze male fertility.

STUDY FUNDING AND COMPETING INTERESTS

This study was supported by the World Health Organization (H9/TSA/037), the National Research Council of Argentina (PIP 2009-290), the National Agency for Scientific and Technological Promotion of Argentina (PICT 2011, 2023) and the Rene Baron Foundation to P.S.C. and by the MEXT of Japan to M.I. The authors declare that there are no conflicts of interest.

The Acrosome Reaction: A Historical Perspective

Acrosome reaction is often referred to as acrosomal exocytosis, but it differs significantly from normal exocytosis. While the vesicle membrane initially holding excreting molecules remains on the cell surface during exocytosis, the outer acrosomal membrane and plasma membrane are lost by forming vesicles during acrosome reaction. In this context, the latter process resembles a release of exosome. However, recent experimental data indicate that the most important roles of acrosome reaction lie not in the release of acrosomal contents (or "vesiculated" plasma and outer acrosomal membrane complexes) but rather in changes in sperm membrane. This review describes the mechanism of fertilization vis-a-vis sperm membrane change, with a brief historical overview of the half-century study of acrosome reaction.

Protein-Carbohydrate Interaction between Sperm and the Egg-Coating Envelope and Its Regulation by Dicalcin, a Xenopus laevis Zona Pellucida Protein-Associated Protein

Protein-carbohydrate interaction regulates multiple important processes during fertilization, an essential biological event where individual gametes undergo intercellular recognition to fuse and generate a zygote. In the mammalian female reproductive tract, sperm temporarily adhere to the oviductal epithelium via the complementary interaction between carbohydrate-binding proteins on the sperm membrane and carbohydrates on the oviductal cells. After detachment from the oviductal epithelium at the appropriate time point following ovulation, sperm migrate and occasionally bind to the extracellular matrix, called the zona pellucida (ZP), which surrounds the egg, thereafter undergoing the exocytotic acrosomal reaction to penetrate the envelope and to reach the egg plasma membrane. This sperm-ZP interaction also involves the direct interaction between sperm carbohydrate-binding proteins and carbohydrates within the ZP, most of which have been conserved across divergent species from mammals to amphibians and echinoderms. This review focuses on the carbohydrate-mediated interaction of sperm with the female reproductive tract, mainly the interaction between sperm and the ZP, and introduces the fertilization-suppressive action of dicalcin, a Xenopus laevis ZP protein-associated protein. The action of dicalcin correlates significantly with a dicalcin-dependent change in the lectin-staining pattern within the ZP, suggesting a unique role of dicalcin as an inherent protein that is capable of regulating the affinity between the lectin and oligosaccharides attached on its target glycoprotein.

The acrosomal protein SP-10 (Acrv1) is an ideal marker for staging of the cycle of seminiferous epithelium in the mouse

The study of spermatogenesis requires accurate identification of the stages of the cycle of the seminiferous epithelium. A stage refers to the unique association of germ cell types at a particular phase of development, as seen in a cross-sectioned seminiferous tubule. Stage-identification, however, is a daunting task. There are 12 stages represented in the mouse seminiferous epithelium. Stages are typically identified on the basis of the morphology of the developing acrosome of spermatids. Although the characteristic features of the acrosome are well-documented in ultrastructure images, a reagent that can highlight the subtle differences in acrosome shape under the light microscope is lacking. Here we demonstrate that a polyclonal antibody raised against the mouse acrosomal protein SP-10 is extremely useful for stage identification. Immunohistochemistry showed that the anti-SP-10 antibody is highly specific for the acrosome of spermatids, as no other cell type in the epithelium showed immunoreactivity. At lower magnification, the gross shape of the acrosome and the increasing intensity of immunostaining served as a guide for the identification of stages I-XII. At higher magnification, characteristic morphological features-such as whether the part of the acrosome that contacts the nuclear surface is round (stage III) or flat (stage IV) or curved (stage VI)-could be identified unambiguously. Overall, we present evidence that SP-10 is a useful marker for staging the cycle of the seminiferous epithelium. The anti-SP-10 antibody works well in different fixatives, on paraffin-embedded as well as cryosections, and has been shown to be useful for characterizing spermatogenic defects in mutant mice.

Unresolved questions concerning mammalian sperm acrosomal exocytosis

In recent years, the study of mammalian acrosomal exocytosis has produced some major advances that challenge the long-held, general paradigms in the field. Principally, the idea that sperm must be acrosome-intact to bind to the zona pellucida of unfertilized eggs, based largely on in vitro fertilization studies of mouse oocytes denuded of the cumulus oophorus, has been overturned by experiments using state-of-the-art imaging of cumulus-intact oocytes and fertilization experiments where eggs were reinseminated by acrosome-reacted sperm recovered from the perivitelline space of zygotes. In light of these results, this minireview highlights a number of unresolved questions and emphasizes the fact that there is still much work to be done in this exciting field. Future experiments using recently advanced technologies should lead to a more complete and accurate understanding of the molecular mechanisms governing the fertilization process in mammals.

Phospholipase B is activated in response to sterol removal and stimulates acrosome exocytosis in murine sperm

Despite a strict requirement for sterol removal for sperm to undergo acrosome exocytosis (AE), the mechanisms by which changes in membrane sterols are transduced into changes in sperm fertilization competence are poorly understood. We have previously shown in live murine sperm that the plasma membrane overlying the acrosome (APM) contains several types of microdomains known as membrane rafts. When characterizing the membrane raft-associated proteomes, we identified phospholipase B (PLB), a calcium-independent enzyme exhibiting multiple activities. Here, we show that sperm surface PLB is activated in response to sterol removal. Both biochemical activity assays and immunoblots of subcellular fractions of sperm incubated with the sterol acceptor 2-hydroxypropyl-β-cyclodextrin (2-OHCD) confirmed the release of an active PLB fragment. Specific protease inhibitors prevented PLB activation, revealing a mechanistic requirement for proteolytic cleavage. Competitive inhibitors of PLB reduced the ability of sperm both to undergo AE and to fertilize oocytes in vitro, suggesting an important role in fertilization. This was reinforced by our finding that incubation either with protein concentrate released from 2-OHCD-treated sperm or with recombinant PLB peptide corresponding to the catalytic domain was able to induce AE in the absence of other stimuli. Together, these results lead us to propose a novel mechanism by which sterol removal promotes membrane fusogenicity and AE, helping confer fertilization competence. Importantly, this mechanism provides a basis for the newly emerging model of AE in which membrane fusions occur during capacitation/transit through the cumulus, prior to any physical contact between the sperm and the oocyte's zona pellucida.

Transitional states of acrosomal exocytosis and proteolytic processing of the acrosomal matrix in guinea pig sperm

In this study, we adapted a FluoSphere bead-binding assay to study the exposure and release of guinea pig sperm acrosomal components during the course of capacitation and acrosomal exocytosis. Prior to capacitation or the initiation of exocytosis, acrosomal proteins were not accessible to FluoSpheres coated with antibodies against two acrosomal matrix (AM) proteins, AM67 and AM50; during the course of capacitation and ionophore-induced acrosomal exocytosis, however, we detected the transient exposure of the solid-phase AM proteins on the surface of guinea pig sperm using the antibody-coated fluorescent beads. Several different transitional stages leading to complete acrosomal exocytosis were classified, and we propose these represent true, functional intermediates since some of the AM proteins are orthologues of mouse proteins that bind the zona pellucida (ZP) of unfertilized eggs. In addition, we present evidence that implicates acrosin in the proteolytic processing of AM50 during AM disassembly. Thus, we propose that the transitional states of acrosomal exocytosis involve early binding of AM proteins to the ZP (by what visually appear to be "acrosome-intact" sperm), maintenance of ZP binding that coincides with the progressive exposure of AM proteins, and gradual proteolytic disassembly of the AM to allow sperm movement through the ZP. We feel this "transitional states" model provides a more refined view of acrosomal function that supports a move away from the widely held, overly simplistic, and binary "acrosome-reaction" model, and embraces a more dynamic view of acrosomal exocytosis that involves intermediate stages of the secretory process in ZP binding and penetration.

Video imaging of the sperm acrosome reaction during in vitro fertilization

Mammalian spermatozoa become competent for fusion with oocytes while traveling through the female reproductive tract and the oocyte's extracellular investments. Recent studies highlighted the molecular mechanism of the sperm's interactions with the zona pellucida (ZP), the extracellular coat surrounding the oocyte. Fertilizing spermatozoa initiate the sperm acrosome reaction (AR), essential for zona penetration and fusion with the oocyte plasma membrane, before they reach the ZP. However, the exact condition of spermatozoa that leads to successful penetration of the ZP remains unknown. We performed microscopic observations of in vitro fertilization with genetically (EGFP) and chemically (antibody and lectin) labeled spermatozoa to monitor the progression of the AR. Spermatozoa exhibiting EGFP(-)/PNA(+) prior to binding to the ZP initiated zona penetration. This result suggests that spermatozoa that have undergone the AR are still capable of binding and penetrating the ZP.

Acrosome reaction in the cumulus oophorus revisited: involvement of a novel sperm-released factor NYD-SP8

Fertilization is a process involving multiple steps that lead to the final fusion of one sperm and the oocyte to form the zygote. One of the steps, acrosome reaction (AR), is an exocytosis process, during which the outer acrosome membrane fuses with the inner sperm membrane, leading to the release of acrosome enzymes that facilitate sperm penetration of the egg investments. Though AR has been investigated for decades, the initial steps of AR in vivo, however, remain largely unknown. A well elucidated model holds the view that AR occurs on the surface of the zona pellucida (ZP), which is triggered by binding of sperm with one of the ZP glycosylated protein, ZP3. However, this model fails to explain the large number of 'falsely' acrosome-reacted sperms found within the cumulus layer in many species examined. With the emerging evidence of cross-talk between sperm and cumulus cells, the potential significance of AR in the cumulus oophorus, the outer layer of the egg, has been gradually revealed. Here we review the acrosome status within the cumulus layer, the cross-talk between sperm and cumulus cells with the involvement of a novel sperm-released factor, NYD-SP8, and re-evaluate the importance and physiological significance of the AR in the cumulus in fertilization.

Cellular mechanisms regulating sperm-zona pellucida interaction

For mammalian spermatozoa to exhibit the ability to bind the zona pellucida (ZP) they must undergo three distinct phases of maturation, namely, spermatogenesis (testis), epididymal maturation (epididymis) and capacitation (female reproductive tract). An impressive array of spermatozoa surface remodeling events accompany these phases of maturation and appear critical for recognition and adhesion of the outer vestments of the oocyte, a structure known as the ZP. It is becoming increasingly apparent that species-specific zona adhesion is not mediated by a single receptor. Instead, compelling evidence now points toward models implicating a multiplicity of receptor-ligand interactions. This notion is in keeping with emerging research that has shown that there is a dynamic aggregation of proteins believed to be important in sperm-ZP recognition to the regions of sperm that mediate this binding event. Such remodeling may in turn facilitate the assembly of a multimeric zona recognition complex (MZRC). Though formation of MZRCs raises questions regarding the nature of the block to polyspermy, formation and assembly of such a structure would no doubt explain the strenuous maturation process that sperm endure on their sojourn to functional maturity.

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.

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.

Functional consequences of cleavage, dissociation and exocytotic release of ZP3R, a C4BP-related protein, from the mouse sperm acrosomal matrix

The acrosome is an exocytotic vesicle located on the apical tip of the sperm head. In addition to having different morphological regions, two biochemically distinct compartments can be defined within the acrosome: a particulate acrosomal matrix and a soluble partition. The domains within the acrosome participate in the release of acrosomal proteins from the sperm during exocytosis, depending on whether the proteins partition into either the soluble or matrix compartments of the acrosome. We have examined the mechanism of differential release by evaluating the solubilization of acrosomal matrix protein ZP3R (sp56) from mouse sperm during the course of spontaneous acrosomal exocytosis. Using indirect immunofluorescence and immunoblotting, we found that the ZP3R monomer is processed from 67,000 M(r) to 43,000 M(r) by proteases coincident with release from the acrosome. Sperm require a maturational step, termed capacitation, before they are competent for acrosomal exocytosis and the processing of ZP3R is dramatically reduced under non-capacitating conditions. The cleavage probably takes place in complement control protein domain (CCP) 6 or the bridge region between CCP6 and CCP7, which is not present in the guinea pig orthologue AM67. The cleaved form of ZP3R does not bind to unfertilized eggs. We have incorporated these structural considerations into a model to explain the functional consequences of acrosomal exocytosis on sperm-zona interactions.

Mammalian fertilization: the strange case of sperm protein 56

During mammalian fertilization sperm bind to the egg's zona pellucida (ZP) after undergoing capacitation. Capacitated mouse sperm bind to mZP3 (one of three ZP glycoproteins), undergo the acrosome reaction, penetrate the ZP, and fuse with egg plasma membrane. Sperm protein 56 (sp56), a member of the C3/C4 superfamily of binding proteins, was identified nearly 20 years ago as a binding partner for mZP3 by photoaffinity cross-linking of acrosome-intact sperm. However, subsequent research revealed that sp56 is a component of the sperm's acrosomal matrix and, for sperm with an intact acrosome, should be unavailable for binding to mZP3. Recently, this dilemma was resolved when it was recognized that some acrosomal matrix (AM) proteins, including sp56, are released to the sperm surface during capacitation. This may explain why uncapacitated mammalian sperm are unable to bind to the unfertilized egg ZP.

Dynamic resolution of acrosomal exocytosis in human sperm

An essential step in mammalian fertilisation is the sperm acrosome reaction (AR) – exocytosis of a single large vesicle (the acrosome) that surrounds the nucleus at the apical sperm head. The acrosomal and plasma membranes fuse, resulting in both the release of factors that might facilitate penetration of the zona pellucida (which invests the egg) and the externalisation of membrane components required for gamete fusion. Exocytosis in somatic cells is a rapid process – typically complete within milliseconds – yet acrosomal enzymes are required throughout zona penetration – a period of minutes. Here, we present the first studies of this crucial and complex event occurring in real-time in individual live sperm using time-lapse fluorescence microscopy. Simultaneous imaging of separate probes for acrosomal content and inner acrosomal membrane show that rapid membrane fusion, initiated at the cell apex, is followed by exceptionally slow dispersal of acrosomal content (up to 12 minutes). Cells that lose their acrosome prematurely (spontaneous AR), compromising their ability to penetrate the egg vestments, are those that are already subject to a loss of motility and viability. Cells undergoing stimulus-induced AR (progesterone or A23187) remain viable, with a proportion remaining motile (progesterone). These findings suggest that the AR is a highly adapted form of exocytosis.

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.

The effect of glycosaminoglycans on rat gametes in vitro and the associated signal pathway

The effects of adding the extracellular glycosaminoglycans (GAGs), hyaluronic acid (HA) and chondroitin sulphate (CS) to ratin vitrofertilisation (IVF) media were assessed. Metaphase II (MII) oocytes were also incubated in GAG-supplemented modified rat 1-cell embryo culture medium (mR1ECM+BSA) for 3 days. Cytoplasmic fragmentation was significantly reduced in mR1ECM+BSA with HA (39.0–48.0%) compared with the control (82.0%). In IVF experiments, neither HA (8.0–30.8%) nor CS (9.7–42.5%) improved fertilisation rates compared with controls fertilised in M16 (47.2%) or enriched Krebs–Ringer bicarbonate solution (61.5%). RT-PCR and Western blot were used to probe for CD44 mRNA and protein in Sprague–Dawley gametes and cumulus cells. CD44 was identified in cumulus cells, suggesting a role for oocyte maturation and cumulus expansion. The CD44 protein was also present on caudal epididymal spermatozoa that were highly stimulated by CSin vitroimplicating a role in fertilisation for CS and CD44.

Proacrosin/acrosin quantification as an indicator of acrosomal integrity in fresh and frozen dog spermatozoa

The scope of the present study was to evaluate the presence and activation of proacrosin/acrosin as a tool to determine the acrosomal status of fresh and frozen/thawed dog spermatozoa. Monoclonal antibody C5F11, directed against human acrosin, cross-reacted with dog spermatozoa and labeled the acrosome of both fresh and frozen/thawed dog spermatozoa. Frozen/thawed spermatozoa had a lesser proportion of labeled spermatozoa than fresh spermatozoa (P<0.05). When live spermatozoa were labeled with soybean trypsin inhibitor conjugated with Alexa 488 (SBTI-Alexa 488), the proportion of acrosome-labeled fresh spermatozoa was less than frozen/thawed spermatozoa (P<0.05). By using Western blots and enzymatic activity, frozen/thawed spermatozoa had a greater proportion of active acrosin than fresh spermatozoa. In addition, beta 1,4-galactosyl-transferase (GalT), a plasma membrane bound protein, remained attached to frozen/thawed spermatozoa. Proacrosin is activated during freezing/thawing of dog spermatozoa, and that proacrosin/acrosin may be a good indicator of acrosomal integrity of frozen/thawed spermatozoa.

Identification of novel gamete receptors that mediate sperm adhesion to the egg coat

Mammalian fertilization is initiated by the species-specific binding of sperm to the zona pellucida, or egg coat. Earlier studies suggested that sperm-egg adhesion in mouse is mediated by the binding of beta1,4-galactosyltransferase-I (GalT) on the sperm surface to specific glycoside ligands on the egg coat glycoprotein, ZP3. Binding of multiple ZP3 oligosaccharides induces GalT aggregation, triggering a pertussis toxin-sensitive G-protein cascade leading to induction of the acrosome reaction. Consistent with this, sperm bearing targeted deletions in GalT are unable to bind ZP3 nor undergo ZP3-dependent acrosomal exocytosis; however, GalT-null sperm are still able to bind to the egg coat. This indicates that sperm-egg binding requires at least two independent binding mechanisms: a GalT-ZP3-independent event that mediates initial adhesion, followed by a GalT-ZP3 interaction that facilitates acrosomal exocytosis. During the past few years, novel GalT-ZP3-independent gamete receptors have been identified that appear to participate in initial gamete adhesion. On such receptor is SED1, an EGF repeat and discoidin domain protein that coats sperm as they traverse through the epididymis, and which is required for sperm to bind the egg coat. Similarly, a novel egg coat ligand is present on ovulated oocytes, but not on ovarian eggs, and which also appears to function in initial sperm binding. The identification of novel gamete receptors that are required for sperm-egg binding opens up new avenues for the development of specific contraceptive strategies.

Immunohistochemical detection of cysteine-rich secretory protein 3 in tissue and in serum from men with cancer or benign enlargement of the prostate gland

BACKGROUND

Recently, the gene for cysteine-rich secretory protein 3 (CRISP-3) was reported to be highly upregulated in prostate cancer (PCa) compared to benign prostatic tissue. The current aims were to investigate diagnostic use of tissue expression and immunodetection in serum of CRISP-3 for detection or monitoring of PCa.

METHODS

Radical prostatectomy specimens and tissue microarrays from transurethral resections and metastases were analyzed for CRISP-3 and PSA by immunohistochemistry. CRISP-3 in tissue homogenates and in serum was measured by an in-house ELISA and PSA by a commercially available immunoassay.

RESULTS

Immunostaining for CRISP-3 in benign prostatic epithelium was generally weak or not detectable. Specific and strong immunostaining was found in a major proportion of cells in high-grade prostatic-intraepithelial-neoplasia (HG-PIN,12/17 patients), in most primary tumors (111/115), and in lymph node (11/15) and bone (12/15) metastases. CRISP-3 immunostaining intensity was regularly strong in areas of Gleason grades 4/5, where PSA-immunoreaction was less intense. Serum levels of CRISP-3 were not different in patients with PCa (n=152) compared to men with BPH (n=81). There was a very weak co-variation between levels of CRISP-3 versus PSA in serum from PCa patients (P<0.05). After orchiectomy, levels of CRISP-3 in serum decreased in median with 11% compared to a 97% median decrease of PSA in serum from 15/20 patients with advanced PCa.

CONCLUSIONS

Strong immunostaining for CRISP-3 is common in HG-PIN and preserved in most PCa specimens, which warrant further immunohistochemical studies of CRISP-3 in PCa. Serum levels of CRISP-3 do not primarily reflect PCa.

Inhibition of the vacuolar H(+)-pump with bafilomycin A1 does not induce acrosome reaction or activate proacrosin in mouse spermatozoa

Acrosomal protease activation is regarded as an important event triggered by acrosomal reaction and leading to sperm passage through zona pellucida. Mammalian acrosome has an internal acid pH that probably helps to maintain inactive proenzymes that otherwise could be precociously activated and prevent normal fertilization. In this work, we have studied the effect of bafilomycin A1, a potent and specific inhibitor of vacuolar H(+)-pump (V-ATPase), on acrosome reaction and proacrosin activation. We used the pH-sensitive probe Lysotracker Green DND-26 to monitor qualitatively intra-acrosomal pH in cauda epididymal mouse spermatozoa. Our results showed that loss of Lysotracker label induced by bafilomycin A1 (acrosome alkalinization) did not induce acrosome reaction or proacrosin activation. We also developed a new technique for imaging the acrosome, and for evaluating the acrosome reaction, in live mouse spermatozoa using Lysotracker DND-26. These results showed that the V-ATPase is a key regulator of mammalian acrosome pH, and that acrosome alkalinization is not the only prerequisite to activate proacrosin under in vivo conditions. Our results suggest that acrosome alkalinization and acrosome reaction are two processes that could be independently regulated during mammalian sperm capacitation.

Novelty of the Pyruvate Metabolic Enzyme Dihydrolipoamide Dehydrogenasein Spermatozoa

Spermatozoa are cells distinctly different from other somatic cells of the body, capacitation being one of the unique phenomena manifested by this gamete. We have shown earlier that dihydrolipoamide dehydrogenase, a post-pyruvate metabolic enzyme, undergoes capacitation-dependent tyrosine phosphorylation, and the functioning of the enzyme is required for hyperactivation (enhanced motility) and acrosome reaction of hamster spermatozoa (Mitra, K., and Shivaji, S. (2004) Biol. Reprod. 70, 887-899). In this report we have investigated the localization of this mitochondrial enzyme in spermatozoa revealing non-canonical extra-mitochondrial localization of the enzyme in mammalian spermatozoa. In hamster spermatozoa, dihydrolipoamide dehydrogenase along with its host complex, the pyruvate dehydrogenase complex, are localized in the acrosome and in the principal piece of the sperm flagella. The localization of dihydrolipoamide dehydrogenase, however, appears to be in the mitochondria in the spermatocytes, but in spermatids it appears to show a juxtanuclear localization (like Golgi). The capacitation-dependent time course of tyrosine phosphorylation of dihydrolipoamide dehydrogenase appears to be different in the principal piece of the flagella and the acrosome in hamster spermatozoa. Activity assays of this bi-directional enzyme suggest a strong correlation between the tyrosine phosphorylation and the bi-directional enzyme activity. This is the first report of a direct correlation of the localization, tyrosine phosphorylation, and activity of the important metabolic enzyme, dihydrolipoamide dehydrogenase, implicating dual involvement and regulation of the enzyme during sperm capacitation.

Human testicular protein TPX1/CRISP-2: localization in spermatozoa, fate after capacitation and relevance for gamete interaction

Testicular protein Tpx-1, also known as CRISP-2, is a cysteine-rich secretory protein specifically expressed in the male reproductive tract. Since the information available on the human protein is limited to the identification and expression of its gene, in this work we have studied the presence and localization of human Tpx-1 (TPX1) in sperm, its fate after capacitation and acrosome reaction (AR), and its possible involvement in gamete interaction. Indirect immunofluorescence studies revealed the absence of significant staining in live or fixed non-permeabilized sperm, in contrast to a clear labelling in the acrosomal region of permeabilized sperm. These results, together with complementary evidence from protein extraction procedures strongly support that TPX1 would be mainly an intra-acrosomal protein in fresh sperm. After in vitro capacitation and ionophore-induced AR, TPX1 remained associated with the equatorial segment of the acrosome. The lack of differences in the electrophoretic mobility of TPX1 before and after capacitation and AR indicates that the protein would not undergo proteolytical modifications during these processes. The possible involvement of TPX1 in gamete interaction was evaluated by the hamster oocyte penetration test. The presence of anti-TPX1 during gamete co-incubation produced a significant and dose-dependent inhibition in the percentage of penetrated zona-free hamster oocytes without affecting sperm motility, the AR or sperm binding to the oolema. Together, these results indicate that human TPX1 would be a component of the sperm acrosome that remains associated with sperm after capacitation and AR, and is relevant for sperm-oocyte interaction.

Biosynthesis and alternate targeting of the lysosomal cysteine protease cathepsin L

Upregulation of cathepsin L expression, whether during development or cell transformation, or mediated by ectopic expression from a plasmid, alters the targeting of the protease and thus its physiological function. Upregulated procathepsin L is targeted to small dense core vesicles and to the dense cores of multivesicular bodies, as well as to lysosomes and to the plasma membrane for selective secretion. The multivesicular vesicles resemble secretory lysosomes characterized in specialized cell types in that they are endosomes that stably store an upregulated protein and they possess the tetraspanin CD63. Morphologically the multivesicular endosomes also resemble late endosomes, but they store procathepsin L, not the active protease, and they are not the major site for LAMP-1 accumulation. Distinction between the lysosomal proenzyme and active protease thus identifies two populations of multivesicular endosomes in fibroblasts, one a storage compartment and one an enzymatically active compartment. A distinctive targeting pathway using aggregation is utilized to enrich the storage endosomes with a particular lysosomal protease that can potentially activate and be secreted.

Differential release of soluble and matrix components: evidence for intermediate states of secretion during spontaneous acrosomal exocytosis in mouse sperm☆

Although its exact role in fertilization is unknown, the acrosome is a very important, exocytotic organelle overlying the anterior aspect of sperm from many species. Structurally and functionally, the acrosome can be considered to consist of soluble and particulate compartments. One component of the particulate acrosomal matrix is the zona pellucida-binding protein sp56. Our demonstration that this protein is within the acrosomal matrix and not on the sperm plasma membrane has led us to reexamine the events of acrosomal exocytosis and the role of the sperm acrosomal matrix in the fertilization process. To visualize the soluble compartment, we have utilized sperm from transgenic mice that carry soluble green fluorescent protein (GFP) in their acrosomes and, as a means to assess the exposure of acrosomal matrix components, we have tested the ability of these sperm to bind beads coated with antibodies to sp56. The loss of GFP from the acrosomes and the binding of the beads by the sperm undergoing capacitation serve as indicators of distinct stages of acrosomal exocytosis, allowing us to define intermediates of acrosomal exocytosis that occur during the course of sperm capacitation. These experiments demonstrate that the exposure and release of acrosomal proteins during spontaneous acrosomal exocytosis is not synchronous but is regulated during capacitation. Furthermore, acrosomal exocytosis under these conditions required calcium in the medium. On the basis of these findings, we propose an alternative model for acrosomal exocytosis that considers a role for these intermediates of exocytosis during capacitation and sperm-ZP interactions.

Disruption of mouse CD46 causes an accelerated spontaneous acrosome reaction in sperm

Human membrane cofactor protein (MCP, CD46) is a ubiquitously expressed protein known to protect cells from complement attack. Interestingly, when we examined the expression of mouse CD46, which we recently cloned, the message was found only in testis and the protein was found on the inner acrosomal membrane of sperm. In order to elucidate the function of CD46, we produced mice carrying a null mutation in the CD46 gene by using homologous recombination. Despite the absence of CD46, the mice were healthy and both sexes were fertile. However, to our surprise, the fertilizing ability of males appeared to be facilitated by disruption of the CD46 gene, as the average number of pups born from CD46(-/-) males was significantly greater than that of wild-type males. It was also revealed that the incidence of the spontaneous acrosome reaction doubled in CD46(-/-) sperm compared to that in wild-type sperm. It was assumed that this increase caused the heightened fertilizing ability found in CD46(-/-) sperm. These data suggest that CD46 may have some role in regulating sperm acrosome reaction.

Control of membrane fusion during spermiogenesis and the acrosome reaction

Membrane fusion is important to reproduction because it occurs in several steps during the process of fertilization. Many events of intracellular trafficking occur during both spermiogenesis and oogenesis. The acrosome reaction, a key feature during mammalian fertilization, is a secretory event involving the specific fusion of the outer acrosomal membrane and the sperm plasma membrane overlaying the principal piece of the acrosome. Once the sperm has crossed the zona pellucida, the gametes fuse, but in the case of the sperm this process takes place through a specific membrane domain in the head, the equatorial segment. The cortical reaction, a process that prevents polyspermy, involves the exocytosis of the cortical granules to the extracellular milieu. In lower vertebrates, the formation of the zygotic nucleus involves the fusion (syngamia) of the male pronucleus with the female pronucleus. Other undiscovered membrane trafficking processes may also be relevant for the formation of the zygotic centrosome or other zygotic structures. In this review, we focus on the recent discovery of molecular machinery components involved in intracellular trafficking during mammalian spermiogenesis, notably related to acrosome biogenesis. We also extend our discussion to the molecular mechanism of membrane fusion during the acrosome reaction. The data available so far suggest that proteins participating in the intracellular trafficking events leading to the formation of the acrosome during mammalian spermiogenesis are also involved in controlling the acrosome reaction during fertilization.

Antisense oligodeoxynucleotides decrease LGL1 mRNA and protein levels and inhibit branching morphogenesis in fetal rat lung

We previously described the cloning of the late gestation lung 1 gene (LGL1), a novel glucocorticoid-inducible gene expressed in the mesenchyme of fetal lung. We report here evidence for a role of the LGL1 gene product (lgl1) in fetal rat lung airway branching morphogenesis, temporal and spatial localization of LGL1 mRNA and lgl1 protein in fetal rat lung, and a correction of the previously published LGL1 sequence. Both the mRNA and protein were detected during fetal lung development. LGL1 mRNA was detected from gestational Day 12 by reverse transcriptase-polymerase chain reaction, and from Day 13 by in situ hybridization. lgl1 protein was detected from Day 18 by Western analysis and from Day 16 by immunohistochemistry. The types of cells expressing LGL1 mRNA and lgl1 protein were assessed by immunohistochemical staining of adjacent serial tissue sections for markers of mesenchymal (vimentin) and smooth muscle (alpha-actin) cells. As gestation advanced, increasing amounts of mRNA and protein were expressed in these cells. In support of a role for lgl1 in airway branching morphogenesis, antisense (but neither sense nor scrambled) oligodeoxynucleotides directed against LGL1 inhibited airway branching in fetal rat lung buds in explant culture, in a dose- and time-dependent manner. The levels of lgl1 protein and LGL1 mRNA expression were decreased in those explants that had inhibited airway branching, compared with the uninhibited controls. Our findings suggest that lgl1 plays an important role in fetal airway branching morphogenesis.

Cell adhesion and fertilization: steps in oocyte transport, sperm-zona pellucida interactions, and sperm-egg fusion

Fertilization in mammals requires the successful completion of many steps, starting with the transport of gametes in the reproductive tract and ending with sperm-egg membrane fusion. In this minireview, we focus on three adhesion steps in this multistep process. The first is oocyte "pick-up," in which the degree of adhesion between the extracellular matrix of the cumulus cells and oviductal epithelial cells controls the successful pick-up of the oocyte-cumulus complex and its subsequent transfer into the oviduct. The second part of this review is concerned with the interaction between the sperm and the zona pellucida of the egg. Evidence is discussed that a plasma membrane form of galactosyltransferase on the surface of mouse sperm binds to ZP3 in the zona pellucida and initiates an acrosome reaction. Additional evidence raises the possibility that initial sperm binding to the zona pellucida is independent of ZP3. Last, we address the relationship between sperm adhesion to the egg plasma membrane and membrane fusion, especially the role of ADAM family proteins on the sperm surface and egg integrins.

N-Acylethanolamines in human reproductive fluids

N-Acylethanolamines (NAEs) are an important family of lipid-signaling molecules. Arachidonylethanolamide (anandamide) (AEA), palmitoylethanolamide (PEA), and oleoylethanolamide (OEA) are co-produced from similar phospholipid precursors when neurons are stimulated. AEA is an endogenous agonist (endocannabinoid) for cannabinoid receptors. It binds with higher affinity to type CB1 than to type CB2 cannabinoid receptors. PEA does not bind to CB1, while the hypothesis that it reacts with putative CB2-like receptors has been questioned. OEA does not activate currently known cannabinoid receptors, but it mimics the effects of AEA and cannabinoids in reducing the fertilizing capacity of sea urchin sperm. OEA and PEA also act as entourage compounds by inhibiting the hydrolysis of AEA by fatty acid amide hydrolase. Cannabinoid receptors and/or AEA are present in mammalian reproductive organs including the testis, epididymis, prostate, ovary, uterus, sperm, preimplantation embryo and placenta, as well as prostatic and mammary carcinomas. We now report that analysis by high-performance liquid chromatography/mass spectrometry (HPLC/MS) shows the presence of AEA, PEA, and OEA in human seminal plasma, mid-cycle oviductal fluid, follicular fluid, amniotic fluid, milk, and fluids from malignant ovarian cysts. Previous studies showed that AEA-signaling via cannabinoid receptors regulates capacitation and fertilizing potential of human sperm, early embryonic development and blastocyst implantation into the uterine mucosa of rodents, as well as proliferation of human mammary and prostatic carcinomas. Current results imply that NAEs also may modulate follicular maturation and ovulation, normal and pathological ovarian function, placental and fetal physiology, lactation, infant physiology, and behavior. Collectively, these findings suggest that NAEs in human reproductive fluids may help regulate multiple physiological and pathological processes in the reproductive system, and imply that exogenous cannabinoids delivered by marijuana smoke might impact these processes. This study has potential medical and public policy ramifications because of the incidence of marijuana abuse by adolescents and adults in our society, previously documented reproductive effects of marijuana, and the ongoing debate about medicinal use of marijuana and cannabinoids.