Osteopontin Reduces Polyspermy During In Vitro Fertilization of Porcine Oocytes1

The evolution of porcine embryo in vitro production

The in vitro production of porcine embryos has presented numerous challenges to researchers over the past four decades. Some of the problems encountered were specific to porcine gametes and embryos and needed the concerted efforts of many to overcome. Gradually, porcine embryo in vitro production systems became more reliable and acceptable rates of blastocyst formation were achieved. Despite the significant improvements, the problem of polyspermic fertilization has still not been adequately resolved and the embryo in vitro culture conditions are still considered to be suboptimal. Whereas early studies focused on increasing our understanding of the reproductive processes involved, the technology evolved to the point where in vitro-matured oocytes and in vitro-produced embryos could be used as research material for developing associated reproductive technologies, such as SCNT and embryo cryopreservation. Today, the in vitro procedures used to mature oocytes and culture embryos are integral to the production of transgenic pigs by SCNT. This review discusses the major achievements, advances, and knowledge gained from porcine embryo in vitro production studies and highlights the future research perspectives of this important technology.

Genomic profiling to improve embryogenesis in the pig

Over the past decade the technology to characterize transcription during embryogenesis has progressed from estimating a single transcript to a reliable description of the entire transcriptome. Northern blots were followed by sequencing ESTs, quantitative real time PCR, cDNA arrays, custom oligo arrays, and more recently, deep sequencing. The amount of information that can be generated is overwhelming. The challenge now is how to glean information from these vast data sets that can be used to understand development and to improve methods for creating and culturing embryos in vitro, and for reducing reproductive loss. The use of ESTs permitted the identification of SPP1 as an oviductal component that could reduce polyspermy. Microarrays identified LDL and NMDA as components to replace BSA in embryo culture media. Deep sequencing implicated arginine, glycine, and folate as components that should be adjusted in our current culture system, and identified a characteristic of embryo metabolism that is similar to cancer and stem cells. Not only will these characterizations aid in improving in vitro production of embryos, but will also be useful for identifying, or creating conditions for donor cells that will be more likely to result in normal development of cloned embryos. The easily found targets have been identified, and now more sophisticated methods are being employed to advance our understanding of embryogenesis. Here the technology to study the global transcriptome is reviewed followed by specific examples of how the technology has been used to understand and improve porcine embryogenesis both in vitro and in vivo.

Deleted in malignant brain tumor 1 is secreted in the oviduct and involved in the mechanism of fertilization in equine and porcine species

Oviductal environment affects preparation of gametes for fertilization, fertilization itself, and subsequent embryonic development. The aim of this study was to evaluate the effect of oviductal fluid and the possible involvement of deleted in malignant brain tumor 1 (DMBT1) on IVF in porcine and equine species that represent divergent IVF models. We first performed IVF after pre-incubation of oocytes with or without oviductal fluid supplemented or not with antibodies directed against DMBT1. We showed that oviductal fluid induces an increase in the monospermic fertilization rate and that this effect is canceled by the addition of antibodies, in both porcine and equine species. Moreover, pre-incubation of oocytes with recombinant DMBT1 induces an increase in the monospermic fertilization rate in the pig, confirming an involvement of DMBT1 in the fertilization process. The presence of DMBT1 in the oviduct at different stages of the estrus cycle was shown by western blot and confirmed by immunohistochemical analysis of ampulla and isthmus regions. The presence of DMBT1 in cumulus–oocyte complexes was shown by western blot analysis, and the localization of DMBT1 in the zona pellucida and cytoplasm of equine and porcine oocytes was observed using immunofluorescence analysis and confocal microscopy. Moreover, we showed an interaction between DMBT1 and porcine spermatozoa using surface plasmon resonance studies. Finally, a bioinformatic and phylogenetic analysis allowed us to identify the DMBT1 protein as well as a DMBT1-like protein in several mammals. Our results strongly suggest an important role of DMBT1 in the process of fertilization.

Locus-specific DNA methylation reprogramming during early porcine embryogenesis

During early mammalian embryogenesis, there is a wave of DNA demethylation postfertilization and de novo methylation around implantation. The paternal genome undergoes active DNA demethylation, whereas the maternal genome is passively demethylated after fertilization in most mammals except for sheep and rabbits. However, the emerging genome-wide DNA methylation landscape has revealed a regulatory and locus-specific DNA methylation reprogramming pattern in mammalian preimplantation embryos. Here we optimized a bisulfite sequencing protocol to draw base-resolution DNA methylation profiles of several selected genes in gametes, early embryos, and somatic tissue. We observed locus-specific DNA methylation reprogramming in early porcine embryos. First, some pluripotency genes (POU5F1 and NANOG) followed a typical wave of DNA demethylation and remethylation, whereas CpG-rich regions of SOX2 and CDX2 loci were hypomethylated throughout development. Second, a differentially methylated region of an imprint control region in the IGF2/H19 locus exhibited differential DNA methylation which was maintained in porcine early embryos. Third, a centromeric repeat element retained a moderate DNA methylation level in gametes, early embryos, and somatic tissue. The diverse DNA methylation reprogramming during early embryogenesis is thought to be possibly associated with the multiple functions of DNA methylation in transcriptional regulation, genome stability and genomic imprinting. The latest technology such as oxidative bisulfite sequencing to identify 5-hydroxymethylcytosine will further clarify the DNA methylation reprogramming during porcine embryonic development.

Triennial Reproduction Symposium: the obstacle course to successful establishment of pregnancy in domestic livestock species

The 2012 Triennial Reproduction Symposium (TRS), "Impediments to Fertility in Domestic Animals," was held immediately before the Joint Annual Meeting of the American Society of Animal Science, American Dairy Science Association, Canadian Society of Animal Science, Western Section of the American Society of Animal Science, and the Asociación Mexicana de Producción Animal in Phoenix, AZ, in July, 2012. The theme of the symposium highlighted key impediments or opportunities in the process of creating a pregnancy, beginning with male and female gametes and ending with a viable fetus. The 2012 TRS was designed to focus on areas of current and exciting investigation across a variety of species and to include 8 presentations from a mix of established and early-career scientists. The TRS was also the venue for presentation of the 2012 L. E. Casida Award for Graduate Education; the recipient was R. D. Randel (Texas A&M University). The symposium provided an excellent opportunity for reproductive biologists to consider the broad spectrum of factors that limit fertility in domestic species and contemplate the current status of knowledge relative to several of the significant obstacles to pregnancy.

Dynamic regulation of sperm interactions with the zona pellucida prior to and after fertilisation

Recent findings have refined our thinking on sperm interactions with the cumulus–oocyte complex (COC) and our understanding of how, at the molecular level, the sperm cell fertilises the oocyte. Proteomic analyses has identified a capacitation-dependent sperm surface reordering that leads to the formation of functional multiprotein complexes involved in zona–cumulus interactions in several mammalian species. During this process, multiple docking of the acrosomal membrane to the plasma membrane takes place. In contrast with the dogma that the acrosome reaction is initiated when spermatozoa bind to the zona pellucida (ZP), it has been established recently that, in mice, the fertilising spermatozoon initiates its acrosome reaction during its voyage through the cumulus before it reaches the ZP. In fact, even acrosome-reacted mouse spermatozoa collected from the perivitelline space can fertilise another ZP-intact oocyte. The oviduct appears to influence the extracellular matrix properties of the spermatozoa as well as the COC. This may influence sperm binding and penetration of the cumulus and ZP, and, in doing so, increase monospermic while decreasing polyspermic fertilisation rates. Structural analysis of the ZP has shed new light on how spermatozoa bind and penetrate this structure and how the cortical reaction blocks sperm–ZP interactions. The current understanding of sperm interactions with the cumulus and ZP layers surrounding the oocyte is reviewed with a special emphasis on the lack of comparative knowledge on this topic in humans, as well as in most farm mammals.

Small RNA profile of the cumulus-oocyte complex and early embryos in the pig

Small RNA represent several unique noncoding RNA classes that have important function in the development of germ cells and early embryonic development. Deep sequencing was performed on small RNA from cumulus cells (recovered from germinal vesicle [GV] and metaphase II-arrested [MII] oocytes), GV and MII oocytes, in vitro fertilization-derived embryos at 60 h postfertilization (4- to 8-cell stage), and Day 6 blastocysts. Additionally, a heterologous miRNA microarray method was also used to identify miRNA expressed in the oocyte during in vitro maturation. Similar to the results of expression analysis of other species, these data demonstrate dynamic expression regulation of multiple classes of noncoding RNA during oocyte maturation and development to the blastocyst stage. Mapping small RNA to the pig genome indicates dynamic distribution of small RNA organization across the genome. Additionally, a cluster of miRNA and Piwi-interacting RNA (piRNA) was discovered on chromosome 6. Many of the small RNA mapped to annotated repetitive elements in the pig genome, of which the SINE/tRNA-Glu and LINE/L1 elements represented a large proportion. Two piRNA (piR84651 and piR16993) and seven miRNA (MIR574, MIR24, LET7E, MIR23B, MIR30D, MIR320, and MIR30C) were further characterized using quantitative RT-PCR. Secretory carrier membrane protein 4 (SCAMP4) was predicted to be subject to posttranscriptional gene regulation mediated by small RNA, by annotating small RNA reads mapped to exonic regions in the pig genome. Consistent with the prediction results, SCAMP4 was further confirmed to be differentially expressed at both transcriptional and translational levels. These data establish a small RNA expression profile of the pig cumulus-oocyte complex and early embryos and demonstrate their potential capacity to be utilized for predictions of functional posttranscriptional regulatory events.

Fertilisation in the horse and paracrine signalling in the oviduct

The mammalian oviduct plays a crucial role in the preparation of gametes for fertilisation (transport and final maturation) and fertilisation itself. An increasing number of studies offers a comprehensive overview of the functions of the oviduct and its secretions, but this topic has had limited investigation in the horse. Limited data are available on the final oocyte maturation in the equine oviduct. However, in vitro and in vivo systems have been established to analyse the influence of equine oviduct epithelial cells (OEC) during maturation on the potential of oocytes for fertilisation and development. Most studies focus on the role of the oviduct in equine sperm function, such as spermatozoa transport, attachment to oviduct epithelium, viability, motility and capacitation. Moreover, some possible candidate molecules for sperm-oviducal interactions have been identified in the horse. Finally, the low efficiency of conventional in vitro fertilisation and the in vivo fertilisation of equine oocytes transferred into the oviduct of an inseminated mare predicted an influence of oviduct in equine fertilisation. Actually, in vivo and in vitro experiments demonstrated a role of the oviduct in equine fertilisation. Moreover, recent studies showed a beneficial effect of homologous and heterologous OEC on equine in vitro fertilisation, and some candidate molecules have been studied.

Biological markers of boar fertility

The semen evaluation techniques used in most commercial artificial insemination centers, which includes sperm motility and morphology measurements, provides a very conservative estimate of the relative fertility of individual boars. As well, differences in relative boar fertility are masked by the widespread use of pooled semen for commercial artificial insemination (AI) in many countries. Furthermore, the relatively high sperm numbers used in commercial AI practice usually compensate for reduced fertility, as can be seen in some boars when lower numbers of sperm are used for AI. The increased efficiency of pork production should involve enhanced use of boars with strong reproductive efficiency and the highest genetic merit for important production traits. Given that the current measures of semen quality are not always indicative of fertility and reproductive performance in boars, accurate and predictive genetic and protein markers are still needed. Recently, significant efforts have been made to identify reliable markers that allow for the identification and exclusion of sires with reduced reproductive efficiency. This paper reviews the current status of proteomic and genomic markers of fertility in boars in relation to other livestock species.

Seminal plasma proteins: what role do they play?

PROBLEM

Semen is a heterogeneous and complex cell suspension in a protein-rich fluid with different functions, some of them well known, others still obscure.

METHOD OF STUDY

This paper reviews, comparatively, our current knowledge on the growing field of proteomics of the SP and its relevance in relation to the in vivo situation, for the sake of reproductive biology, diagnostics and treatment.

RESULTS

Ejaculated spermatozoa, primarily bathing in cauda epididymal fluid, are (in vitro) bulky, exposed to most, if not all, secretions from the accessory sexual glands. In vivo, however, not all spermatozoa are necessarily exposed to all secretions from these glands, because sperm cohorts are delivered in differential order and bathe in seminal plasma (SP) with different concentrations of constituents, including peptides and proteins. Proteins are relevant for sperm function and relate to sperm interactions with the various environments along the female genital tract towards the oocyte vestments. Specific peptides and proteins act as signals for the female immune system to modulate sperm rejection or tolerance, perhaps even influencing the relative intrinsic fertility of the male and/or couple by attaining a status of maternal tolerance towards embryo and placental development.

CONCLUSIONS

Proteins of the seminal plasma have an ample panorama of action, and some appear responsible for establishing fertility.

The tunica mucosa of the oviduct in case of ovarian cysts presence in sows

The unfavorable morphological changes in the oviductal mucosa may lead to infertility in females and be one of the reasons for slaughtering of farm animals. The aim of study was to investigate the morphological changes in the epithelium of oviductal mucosa of sows with ovarian cysts. The oviducts of 18 sows were obtained after slaughter. Sows were divided into three groups: 1st group - 6 sows with polycystic ovaries, 2nd group - 6 sows with single cysts, 3rd group - 6 sows without ovarian cysts. The epithelium was examined by light microscopy, SEM and TEM. Ciliated and secretory cells were count on 150 μm segments in apical and basal zone of folds both in ampulla and isthmus. We analyzed the number of cells in 5 folds in both these oviductal parts in dexter and sinister oviduct. We have noted unfavorable changes in oviductal mucosa consisting in increase of the secretory cells with simultaneous decrease of ciliated cells. The correlations between the general occurrence of ovarian cysts and the morphological state of epithelium of oviductal tunica mucosa were determined. The changes in proportion of cells occurred both in ampulla and isthmus. The excessive secretion covering epithelium promotes agglutinations and adhesions of the tubal folds and occlusion of the oviduct. These alterations may create problems in the migration of gametes and prevent the movements of the zygote towards the uterus and cause some disturbances in conceptus development in its early stages. Results suggest that COD is connected with unfavorable morphological and functional changes within epithelium of the oviductal tunica mucosa.

Histone deacetylase inhibitors improve in vitro and in vivo developmental competence of somatic cell nuclear transfer porcine embryos

Faulty epigenetic reprogramming of somatic nuclei is likely to be a major cause of low success observed in all mammals produced through somatic cell nuclear transfer (SCNT). It has been demonstrated that the developmental competence of SCNT embryos in several species were significantly enhanced via treatment of histone deacetylase inhibitors (HDACi) such as trichostatin A (TSA) to increase histone acetylation. Here we report that 50 nM TSA for 10 h after activation increased the developmental competence of porcine SCNT embryos constructed from Landrace fetal fibroblast cells (FFCs) in vitro and in vivo, but not at higher concentrations. Therefore, we optimized the application of another novel HDACi, Scriptaid, for development of porcine SCNT embryos. We found that treatment with 500 nM Scriptaid significantly enhanced the development SCNT embryos to the blastocyst stage when outbred Landrace FFCs and ear fibroblast cells (EFCs) were used as donors compared to the untreated group. Scriptaid increased the overall cloning efficiency from 0.4% (untreated group) to 1.6% for Landrace FFCs and 0 to 3.7% for Landrace EFCs. Moreover, treatment of SCNT embryos with Scriptaid improved the histone acetylation on Histone H4 at lysine 8 (AcH4K8) in a pattern similar to that of the in vitro fertilized (IVF) embryos.

What controls polyspermy in mammals, the oviduct or the oocyte?

A block to polyspermy is required for successful fertilisation and embryo survival in mammals. A higher incidence of polyspermy is observed during in vitro fertilisation (IVF) compared with the in vivo situation in several species. Two groups of mechanisms have traditionally been proposed as contributing to the block to polyspermy in mammals: oviduct-based mechanisms, avoiding a massive arrival of spermatozoa in the proximity of the oocyte, and egg-based mechanisms, including changes in the membrane and zona pellucida (ZP) in reaction to the fertilising sperm. Additionally, a mechanism has been described recently which involves modifications of the ZP in the oviduct before the oocyte interacts with spermatozoa, termed "pre-fertilisation zona pellucida hardening". This mechanism is mediated by the oviductal-specific glycoprotein (OVGP1) secreted by the oviductal epithelial cells around the time of ovulation, and is reinforced by heparin-like glycosaminoglycans (S-GAGs) present in oviductal fluid. Identification of the molecules contributing to the ZP modifications in the oviduct will improve our knowledge of the mechanisms of sperm-egg interaction and could help to increase the success of IVF systems in domestic animals and humans.

The secretions of oviduct epithelial cells increase the equine in vitro fertilization rate: are osteopontin, atrial natriuretic peptide A and oviductin involved?

BACKGROUND

Oviduct epithelial cells (OEC) co-culture promotes in vitro fertilization (IVF) in human, bovine and porcine species, but no data are available from equine species. Yet, despite numerous attempts, equine IVF rates remain low. Our first aim was to verify a beneficial effect of the OEC on equine IVF. In mammals, oviductal proteins have been shown to interact with gametes and play a role in fertilization. Thus, our second aim was to identify the proteins involved in fertilization in the horse.

METHODS & RESULTS

In the first experiment, we co-incubated fresh equine spermatozoa treated with calcium ionophore and in vitro matured equine oocytes with or without porcine OEC. We showed that the presence of OEC increases the IVF rates. In the subsequent experiments, we co-incubated equine gametes with OEC and we showed that the IVF rates were not significantly different between 1) gametes co-incubated with equine vs porcine OEC, 2) intact cumulus-oocyte complexes vs denuded oocytes, 3) OEC previously stimulated with human Chorionic Gonadotropin, Luteinizing Hormone and/or oestradiol vs non stimulated OEC, 4) in vivo vs in vitro matured oocytes. In order to identify the proteins responsible for the positive effect of OEC, we first searched for the presence of the genes encoding oviductin, osteopontin and atrial natriuretic peptide A (ANP A) in the equine genome. We showed that the genes coding for osteopontin and ANP A are present. But the one for oviductin either has become a pseudogene during evolution of horse genome or has been not well annotated in horse genome sequence. We then showed that osteopontin and ANP A proteins are present in the equine oviduct using a surface plasmon resonance biosensor, and we analyzed their expression during oestrus cycle by Western blot. Finally, we co-incubated equine gametes with or without purified osteopontin or synthesized ANP A. No significant effect of osteopontin or ANP A was observed, though osteopontin slightly increased the IVF rates.

CONCLUSION

Our study shows a beneficial effect of homologous and heterologous oviduct cells on equine IVF rates, though the rates remain low. Furthers studies are necessary to identify the proteins involved. We showed that the surface plasmon resonance technique is efficient and powerful to analyze molecular interactions during fertilization.

Acid peptidase activity released from in vitro produced porcine embryos: a candidate marker to predict developmental competence

The ability to efficiently create high quality embryos, competent to produce normal viable offspring in vitro, facilitates diverse technological advancements in animal agriculture and assisted reproduction. Current methods for evaluation of embryos are predominantly based on morphological characteristics which are prone to potential bias of the scorer. Metabolic and genetic markers have also been explored for quality assessment, but they are cost prohibitive or require longer periods of time for evaluation. We hypothesized that secreted enzymes could provide another means of embryo quality assessment. In this report, we provide evidence that medium conditioned by porcine embryos often has proteolytic activity that operates in acidic conditions (acid peptidase activity or APA). The APA could be inhibited by pepstatin A, suggesting that the activity is derived from one or more aspartic peptidases. We also provide evidence that single embryos, incubated for as few as 24 hr, released enough APA that it was possible to measure it accurately at day 5 of culture. We also observed that such activity on day 6 could be positively correlated with advanced developmental stage and embryo quality. In addition, those embryos that were graded identically by morphological evaluations often differed in the amount of APA--with some being significantly higher than the experimental threshold value. Therefore, the APA of embryos might serve as an additional marker for evaluation of embryos.

Pre-fertilization zona pellucida hardening by different cross-linkers affects IVF in pigs and cattle and improves embryo production in pigs

Zona pellucida (ZP) hardening (resistance to proteolysis) has been classically identified as a post-fertilization event that contributes to the block to polyspermy. Di-(N-succinimidyl)-3,3′-dithiodipropionate (DSP), a permeable amine-reactive cross-linker, was recently shown to induce pre-fertilization ZP hardening and to improve porcine IVF productivity. The objectives of this study were to investigate i) how DSP affects pre-fertilization ZP hardening and IVF in cattle, ii) if a non-permeable amine-reactive cross-linker such as bis(sulfosuccinimidyl) suberate (BS3) affects ZP hardening and IVF in cattle and pigs, and iii) whether DSP or BS3, if improvement in IVF productivity was demonstrated in either species, affectsin vitroembryo development. Bovine and porcinein vitromatured oocytes were incubated with the cross-linkers (0.06, 0.3, and 0.6 mg/ml) for 30 min. Then they were subjected to ZP digestion or IVF. In cattle, both DSP and BS3 induced ZP hardening and decreased the penetration rate, although monospermy, penetration, or male pronuclear formation was not affected. In pigs, BS3 treatment induced ZP hardening, decreased penetration and male pronuclear formation, and increased monospermy. IVF productivity only improved when porcine oocytes were exposed to DSP. When porcine zygotes derived from this treatment were further culturedin vitro, the cleavage and blastocyst formation rates increased. These results support the idea that mechanisms involved in the prevention of polyspermic fertilization in cattle and pigs have different efficiencies, and ZP hardening induced by DSP cross-linker may be useful for improving porcine embryo production.

Significant improvement in cloning efficiency of an inbred miniature pig by histone deacetylase inhibitor treatment after somatic cell nuclear transfer

The National Institutes of Health (NIH) miniature pig was developed specifically for xenotransplantation and has been extensively used as a large-animal model in many other biomedical experiments. However, the cloning efficiency of this pig is very low (<0.2%), and this has been an obstacle to the promising application of these inbred swine genetics for biomedical research. It has been demonstrated that increased histone acetylation in somatic cell nuclear transfer (SCNT) embryos, by applying a histone deacetylase (HDAC) inhibitor such as trichostatin A (TSA), significantly enhances the developmental competence in several species. However, some researchers also reported that TSA treatment had various detrimental effects on the in vitro and in vivo development of the SCNT embryos. Herein, we report that treatment with 500 nM 6-(1,3-dioxo-1H, 3H-benzo[de]isoquinolin-2-yl)-hexanoic acid hydroxyamide (termed scriptaid), a novel HDAC inhibitor, significantly enhanced the development of SCNT embryos to the blastocyst stage when NIH inbred fetal fibroblast cells (FFCs) were used as donors compared with the untreated group (21% vs. 9%, P < 0.05). Scriptaid treatment resulted in eight pregnancies from 10 embryo transfers (ETs) and 14 healthy NIH miniature pigs from eight litters, while no viable piglets (only three mummies) were obtained from nine ETs in the untreated group. Thus, scriptaid dramatically increased the cloning efficiency when using inbred genetics from 0.0% to 1.3%. In contrast, scriptaid treatment decreased the blastocyst rate in in vitro fertilization embryos (from 37% to 26%, P < 0.05). In conclusion, the extremely low cloning efficiency in the NIH miniature pig may be caused by its inbred genetic background and can be improved by alteration of genomic histone acetylation patterns.

Oviduct-specific glycoprotein and heparin modulate sperm-zona pellucida interaction during fertilization and contribute to the control of polyspermy

Polyspermy is an important anomaly of fertilization in placental mammals, causing premature death of the embryo. It is especially frequent under in vitro conditions, complicating the successful generation of viable embryos. A block to polyspermy develops as a result of changes after sperm entry (i.e., cortical granule exocytosis). However, additional factors may play an important role in regulating polyspermy by acting on gametes before sperm-oocyte interaction. Most studies have used rodents as models, but ungulates may differ in mechanisms preventing polyspermy. We hypothesize that zona pellucida (ZP) changes during transit of the oocyte along the oviductal ampulla modulate the interaction with spermatozoa, contributing to the regulation of polyspermy. We report here that periovulatory oviductal fluid (OF) from sows and heifers increases (both, con- and heterospecifically) ZP resistance to digestion with pronase (a parameter commonly used to measure the block to polyspermy), changing from digestion times of approximately 1 min (pig) or 2 min (cattle) to 45 min (pig) or several hours (cattle). Exposure of oocytes to OF increases monospermy after in vitro fertilization in both species, and in pigs, sperm-ZP binding decreases. The resistance of OF-exposed oocytes to pronase was abolished by exposure to heparin-depleted medium; in a medium with heparin it was not altered. Proteomic analysis of the content released in the heparin-depleted medium after removal of OF-exposed oocytes allowed the isolation and identification of oviduct-specific glycoprotein. Thus, an oviduct-specific glycoprotein-heparin protein complex seems to be responsible for ZP changes in the oviduct before fertilization, affecting sperm binding and contributing to the regulation of polyspermy.

Osteopontin improves in vitro development of porcine embryos and decreases apoptosis

An optimal environment for fertilization and early embryonic development is provided by the mammalian oviduct and uterus. The secretory cells lining the lumen of the oviduct and uterus synthesize and secrete proteins that have been shown to interact with and influence the activities of gametes and embryos. Western blotting in this study demonstrated that a 50-kDa secreted phosphoprotein 1 (SPP1) form was present in the uterus on Days 0, 3, and 5 in pregnant and nonbred gilts, and the concentration of SPP1 on Day 0 was higher than on Days 3 and 5 in pregnant gilts, but in nonbred gilts the concentration of SPP1 on Day 0 was higher than Day 3, but not Day 5. In addition, we show that addition of 0.1 microg/ml SPP1 to the culture medium after fertilization increased the percent cleaved (24 hr: 23.6 +/- 1.29(a) vs. 18.7 +/- 0.65(b) (2-cell %)), and the percent blastocyst (37.2 +/- 1.12(a) vs. 30.9 +/- 0.56(b)) derived from IVF (P < 0.05). In parthenogenetic-derived embryos the percent cleaved was increased due to SPP1 at 24 hr (24.0 +/- 1.59(a) vs. 19.7 +/- 1.59(b) (>2-cell %)), and at 48 hr (72.9+/- 2.99(a) vs. 63.3 +/- 2.99(b)), but not the percent blastocyst. By TUNEL assay, SPP1 decreased both apoptosis (7.9 +/- 0.04(a) vs. 13.1 +/- 0.02(b)) and the percent fragmentation (45.2 +/- 0.07(a) vs. 58.8 +/- 0.03(b)). We conclude that SPP1 can improve development in vitro possibly by reducing the rate of apoptosis.

Ubiquitin C-terminal hydrolase-activity is involved in sperm acrosomal function and anti-polyspermy defense during porcine fertilization

The 26S proteasome, which is a multi-subunit protease with specificity for substrate proteins that are postranslationally modified by ubiquitination, has been implicated in acrosomal function and sperm-zona pellucida (ZP) penetration during mammalian fertilization. Ubiquitin C-terminal hydrolases (UCHs) are responsible for the removal of polyubiquitin chains during substrate priming for proteasomal proteolysis. The inhibition of deubiquitination increases the rate of proteasomal proteolysis. Consequently, we have hypothesized that inhibition of sperm acrosome-borne UCHs increases the rate of sperm-ZP penetration and polyspermy during porcine in vitro fertilization (IVF). Ubiquitin aldehyde (UA), which is a specific nonpermeating UCH inhibitor, significantly (P < 0.05) increased polyspermy during porcine IVF and reduced (P < 0.05) UCH enzymatic activity measured in motile boar spermatozoa using a specific fluorometric UCH substrate, ubiquitin-AMC. Antibodies against two closely related UCHs, UCHL1 and UCHL3, detected these UCHs in the oocyte cortex and on the sperm acrosome, respectively, and increased the rate of polyspermy during IVF, consistent with the UA-induced polyspermy surge. In the oocyte, UCHL3 was primarily associated with the meiotic spindle. Sperm-borne UCHL3 was localized to the acrosomal surface and coimmunoprecipitated with a peripheral acrosomal membrane protein, spermadhesin AQN1. Recombinant UCHs, UCHL3, and isopeptidase T reduced polyspermy when added to the fertilization medium. UCHL1 was detected in the oocyte cortex but not on the sperm surface, and was partially degraded 6-8 h after fertilization. Enucleated oocyte-somatic cell electrofusion caused polarized redistribution of cortical UCHL1. We conclude that sperm-acrosomal UCHs are involved in sperm-ZP interactions and antipolyspermy defense. Modulation of UCH activity could facilitate the management of polyspermy during IVF and provide insights into male infertility.

Detection of osteopontin on Holstein bull spermatozoa, in cauda epididymal fluid and testis homogenates, and its potential role in bovine fertilization

Osteopontin (OPN) is a secreted extracellular matrix phosphoprotein identified in various tissues and fluids including those of the male and female reproductive tracts. OPN was previously identified as a 55 kDa high fertility marker in Holstein bull seminal plasma, produced by the ampulla and the vesicular gland. The objectives of this study were to characterize OPN on ejaculated and cauda epididymal sperm using immunofluorescence and western blot analysis, and to assess the role of sperm OPN in fertilization. Solubilized sperm membrane proteins from ejaculated and cauda epididymal sperm were separated by 1D SDS-PAGE, transferred to nitrocellulose, and probed with an antibody to bovine milk OPN. A 35 kDa protein was detected by this antibody in both ejaculated and cauda epididymal sperm membranes. Analyses also recognized OPN at 55 and 25 kDa in cauda epididymal fluid and testicular parenchyma homogenates respectively. Immunofluorescent analysis of ejaculated and cauda epididymal sperm showed OPN localization in a well-defined band in the postacrosomal region of the sperm head and also on the midpiece. Results ofin vitrofertilization experiments showed that sperm treated with an antibody to OPN fertilized fewer oocytes than sperm treated with control medium while increasing incidence of polyspermy, suggesting a role of sperm-associated OPN in fertilization and a block to polyspermy. These studies demonstrate that OPN exists at multiple molecular weight forms in the bull reproductive tract and its presence on ejaculated sperm may signal its importance in fertilization by interacting with integrins or other proteins on the oocyte plasma membrane.