De novo protein synthesis by bovine uterine tube (oviduct) epithelial cells changes during co-culture with bull spermatozoa

Molecules involved in the sperm interaction in the human uterine tube: a histochemical and immunohistochemical approach

In humans, even where millions of spermatozoa are deposited upon ejaculation in the vagina, only a few thousand enter the uterine tube (UT). Sperm transiently adhere to the epithelial cells lining the isthmus reservoir, and this interaction is essential in coordinating the availability of functional spermatozoa for fertilization. The binding of spermatozoa to the UT epithelium (mucosa) occurs due to interactions between cell-adhesion molecules on the cell surfaces of both the sperm and the epithelial cell. However, in humans, there is little information about the molecules involved. The aim of this study was to perform a histological characterization of the UT focused on determining the tissue distribution and deposition of some molecules associated with cell adhesion (F-spondin, galectin-9, osteopontin, integrin αV/β3) and UT's contractile activity (TNFα-R1, TNFα-R2) in the follicular and luteal phases. Our results showed the presence of galectin-9, F-spondin, osteopontin, integrin αV/β3, TNFα-R1, and TNFα-R2 in the epithelial cells in ampullar and isthmic segments during the menstrual cycle. Our results suggest that these molecules could form part of the sperm-UT interactions. Future studies will shed light on the specific role of each of the identified molecules.

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.

Advances in understanding mechanisms of long-term sperm storage-the soft-shelled turtle model

Long-term sperm storage is a special reproductive strategy, which can extend the time window between mating and fertilization in some animal species. Spermatozoa of the soft-shelled turtle, Pelodiscus sinensis, can be stored in the epididymis and oviduct for at least six months and one year, respectively. How spermatozoa can be stored in vivo for such a prolonged period is yet to be explained. We analyze the mechanisms that contribute to long-term sperm storage in P. sinensis, and compare them with other species from three different perspectives: the spermatozoon itself, the storage microenvironment and the interaction between the spermatozoon and microenvironment. Characteristics of soft-shelled turtle spermatozoa itself, such as the huge cytoplasmic droplet with its content of several large lipid droplets (LDs) and onion-like mitochondira, facilitate long-term sperm storage. The microenvironment of reproductive tract, involving in the secretions, structural barriers, exosomes, androgen receptors, Toll-like receptors and survival factor Bcl-2, are important for the maintenance of spermatozoa long-term storage. Sperm heads are always embedded among the oviductal cilia and even intercalate into the apical hollowness of the ciliated cells, indicating that the ciliated cells support the stored spermatozoa. RNA seq is firstly used to detect the molecular mechanism of sperm storage, which shows that autophagy, apoptosis and immune take part in the long-term sperm storage in this species.

Can the antral follicular count modulate the gene expression of bovine oviducts in Aberdeen Angus and Nelore heifers?

The number of visible ovarian antral follicles (antral follicle count—AFC) is repeatable in bovine individuals, but highly variable between animals, and with differences between Bos taurus and Bos indicus breeds. Several studies have tried to determine the correlation between AFC and increased fertility in cattle. While the impacts of AFC on embryo production, hormonal levels, and pregnancy rates have been described, the molecular effects of AFC on bovine oviducts have not yet been investigated. Here, the aim was to investigate the impact of breeds, such as Aberdeen Angus and Nelore heifer with high or low AFC, on abundance of transcripts and protein related to oviductal transport, sperm reservoir formation, monospermy control, and gamete interaction in the oviducts. In summary, the ovulation side was the major factor that affected transcript abundance on bovine oviducts. However, a discreet effect among AFC and cattle breeds was also observed. Based on this, we concluded and reinforced here that differential microenvironments between ipsilateral and contralateral oviducts have a major effect on modulating the transcripts related to oviductal transport, sperm reservoir formation, monospermy control, and gamete interaction. However, we cannot exclude that there is minimal effect of AFC or breed on regulation of some genes (such as AGTR1, ACE1, FUCA1, and VEGFA) in bovine oviducts.

The role of mating in oviduct biology

The oviduct connects the ovary to the uterus, and is subject to changes that influence gamete transport, fertilization, and early embryo development. The ovarian steroids estradiol and progesterone are largely responsible for regulating oviduct function, although mating signals also affect the female reproductive tract, both indirectly, through sensory stimulation, and directly, through contact with seminal plasma or spermatozoa. The resulting alterations in gene and protein expression help establish a microenvironment that is appropriate for sperm storage and selection, embryo development, and gamete transport. Mating may also induce the switch from a non-genomic to a genomic pathway of estradiol-accelerated oviduct egg transport, reflecting a novel example of the functional plasticity in well-differentiated cells. This review highlights the physiological relevance of various aspects of mating to oviduct biology and reproductive success. Expanding our knowledge of the mating-associated molecular and cellular events in oviduct cells would undoubtedly facilitate new therapeutic strategies to treat infertility attributable to oviduct pathologies. Mol. Reprod. Dev. 83: 875-883, 2016 © 2016 Wiley Periodicals, Inc.

Introduction: A Brief Guide to the Periconception Environment

Definition of the periconception period is not an exact science and is probably somewhat arbitrary. One can define it as spanning the period from the final stages of gamete maturation until formation of the embryo and the stages of embryonic development and implantation. Hence, the periconception period includes periods when spermatozoa are in the female reproductive tract, oocytes are matured and ovulated into the oviduct, fertilization occurs and the embryo undergoes development. By definition the implantation process and the early stages of placenta formation are also regarded as a part of the periconception period. In this article we highlight a few of the major advances which have transformed this topic over the last two decades. It is now clear that the fitness and wellbeing of developing mammalian embryos, including the human, are highly dependent on the health status, diet and habits of both parents especially in the months and weeks that precede the formation of oocytes and spermatozoa.

Cross talk during the periconception period

The cross talk between gametes, embryos, and female reproductive tract plays a crucial role in fine tuning of different reproductive events as well as influencing the epigenetic profile of offspring and their health in adulthood. Here, we describe some background to the recent investigations leading to the discovery of this cross talk. We will also point to important requirements for understanding the maternal communication with gametes and embryos. Finally, we mention two probable hypotheses regarding how gametes and embryos are recognized by the female reproductive tract. It is clear that understanding this cross talk is leading to the production of new means for increasing fertility and potentials for affecting the epigenomic profile of an individual.

Extracellular Vesicles from BOEC in In Vitro Embryo Development and Quality

To evaluate the effect of conditioned media (CM) and Extracellular Vesicles (EVs) derived from bovine oviduct epithelial cell (BOEC) lines on the developmental capacity of bovine zygotes and the quality of embryos produced in vitro, presumptive zygotes were cultured under specific conditions. In experiment 1, zygotes were cultured either on monolayers from BOEC extended culture (E), together with fresh BOEC suspension cells, or with BOEC-CM from fresh or E-monolayers. In experiment 2, EVs were isolated from BOEC-CM and characterized (150-200 nm) by Nanosight® and electron microscopy. Zygotes were cultured in the presence of 3x10(5) EVs/mL, 1.5x10(5) EVs/mL or 7.5x10(4) EVs/mL of fresh or frozen BOEC-EVs. In experiment 3, zygotes were cultured in absence of FCS but with EVs from BOEC-E that had been cultured in different culture media. In experiment 4, zygotes were cultured in SOF+5% normal-FCS, or EV-depleted-FCS. In all cases, cleavage rate (Day 2) and blastocyst development (Day 7-9) was assessed. Blastocysts on Days 7/8 were used for quality evaluation through differential cell count, cryotolerance and gene expression patterns. No differences were found among all FCS-containing groups in cleavage rate or blastocyst yield. However, embryos derived from BOEC-CM had more trophectoderm cells, while embryos derived from BOEC-EVs, both fresh and frozen, has more trophectoderm and total cells. More embryos survived vitrification in the BOEC-CM and BOEC-EV groups. In contrast, more embryos survived in the EV-depleted-FCS than in normal-FCS group. Gene expression patterns were modified for PAG1 for embryos cultured with EVs in the presence of FCS and for IFN-T, PLAC8, PAG1, CX43, and GAPDH in the absence of FCS. In conclusion, EVs from FCS have a deleterious effect on embryo quality. BOEC-CM and EVs during in vitro culture had a positive effect on the quality of in vitro produced bovine embryos, suggesting that EVs have functional communication between the oviduct and the embryo in the early stages of development.

Sperm Storage in the Female Reproductive Tract

The capacity for sperm storage within the female reproductive tract occurs widely across all groups of vertebrate species and is exceptionally well developed in some reptiles (maximum duration seven years) and fishes (maximum duration >1 year). Although there are many reports on both the occurrence of female sperm storage in diverse species and its adaptive benefits, few studies have been directed toward explaining the mechanisms involved. In this article we review recent findings in birds and mammals in an effort to develop hypotheses that could be translated into research applications in animal breeding technologies. There are pockets of evidence to suggest that the local epithelial cells, sometimes arranged as sperm storage tubules, can respond to spermatozoa by producing heat shock proteins as well as providing an environment rich in antioxidants. Moreover, the local immune system seems to tolerate the arrival of spermatozoa, while retaining the ability to combat the arrival of infectious microorganisms.

B-cell lymphoma-2 localization in the female reproductive tract of the Chinese soft-shelled turtle, Pelodiscus sinensis and its relationship with sperm storage

The aim of the present study was to investigate the expression and localization of B-cell lymphoma-2 (Bcl-2) in the oviduct of the Chinese soft-shelled turtle, Pelodiscus sinensis, during the reproductive cycle to analyze the relationship between Bcl-2 and sperm storage. Bcl-2 expression was confirmed in the P. sinensis oviduct by western blot analysis. Hematoxylin-eosin staining showed that female P. sinensis stored sperm from November to April of the following year. The oviduct showed positive immunostaining for Bcl-2 of epithelial ciliated cells, gland ducts, and gland cells. Bcl-2 expression in the oviduct was associated with sperm storage occurrence. This indicates that the survival factor Bcl-2 may play a role in P. sinensis sperm storage.

Optimisation of proteomic approaches to study the maternal interaction with gametes in sow's reproductive tract

The applications of 2DE and MS have been successfully used in many studies utilising different biological samples. The complex nature of cellular proteomes is a big challenge for proteomic technologies. Much effort has been applied to develop and improve the preparation techniques for proteomic samples to be able to detect the low abundant proteins. This is one of the major and unsolved challenges facing the proteomic analysis of biological samples. One partial remedy is to deplete the proteomic samples. In this study, we compared two techniques (acetone precipitation and commercial kit) for the cleaning and purification of oviductal and uterine horn secretory proteomes in primary cell culture system. The samples prepared from acetone precipitation and commercial kit 2-D clean up kit were compared by 2-dimentioanl electrophoresis. We found that no significant difference was observed in number of spots detected between the samples prepared by acetone precipitation technique to those prepared by commercial kit. Protein samples were run through strong cation exchange (SCX) liquid chromatography in order to fractionate samples of major proteins. Protein identification by mass spectrometry revealed a significant detection of low abundant proteins in comparing to high abundant proteins. In conclusion, acetone precipitation was found to be more efficient and cost effect technique. Depletion of proteomic samples from the most abundant protein species is strongly recommended to allow the mid and low abundant protein to be detected. A better resolution of the gels will be achieved by removing the major proteins such as albumin and immunoglobulin.

Mechanisms of sperm storage in the female reproductive tract: an interspecies comparison

Once semen has been collected for artificial insemination, it is diluted into extenders designed to prevent its deterioration over the period prior to insemination. If the semen is not frozen, the extenders provide protection for a period of a few hours to a few days, depending on species. Despite the efforts of biotechnologists to increase the duration of storage without compromising fertility, there has been relatively little progress for many years. However, comparative studies in diverse species have revealed that long-term sperm storage (up to months and years) within the female reproductive tract is relatively commonplace in reptiles, fishes, birds and amphibians. Even among mammals, some species of bat have evolved mechanisms for storing spermatozoa for several months in the uterus or oviduct so that they can mate in the autumn but postpone fertilization until the spring. We currently know little about the mechanisms that support such long-term sperm storage, mainly because evidence from such species is either absent or fragmentary. Nevertheless, parallels between mammalian and other systems, where spermatozoa are sequestered in sperm storage tubules, suggest that the enclosure of spermatozoa within pockets of epithelial cells may be sufficient to achieve long-term sperm storage. In addition, recent evidence from sperm-storing bats has suggested an alternative, or additional, hypothesis that the modulation of apoptosis within epithelial cells is important in controlling sperm survival. Despite a lack of direct experimental evidence from a wide variety of species, I propose that there is now enough evidence to warrant investigation of these hypotheses.

Components of oviduct physiology in eutherian mammals

Recalling the evolutionary sequence of development first of gonad and subsequently of oviducts, ovarian endocrine regulation of all known components of oviduct physiology is reviewed. Ovaries not only influence oviducts via the systemic blood circulation, but also locally by counter-current transfer of relatively high concentrations of steroid hormones and prostaglandins between the ovarian vein and oviduct branch of the ovarian artery. The efficiency and impact of such counter-current transfer is greatest around the time of ovulation, the transfer process receiving further inputs from hormones present in peritoneal fluid. Classical oviduct physiology is summarised, and the potential molecular consequences of temperature gradients within the duct lumen examined. At ovulation, an oocyte-cumulus complex is displaced in minutes from the follicular surface to the site of fertilisation at the ampullary-isthmic junction of the oviduct. This rapid initial phase is contrasted with the subsequent slow progression of embryos to the uterus in days, still encompassed within a zona pellucida. Regarding transport of spermatozoa, the formation of a pre-ovulatory reservoir in the caudal portion of the oviduct isthmus is noted, with suppression of motility and sperm-head binding to epithelial organelles acting to maintain fertilising ability. Completion of capacitation is prompted shortly before ovulation, predominantly by Ca(2+) influx into bound spermatozoa. A controlled release of spermatozoa coupled with their hyperactivation results in initial sperm:egg ratios at the site of fertilisation close to unity, thereby avoiding the pathological condition of polyspermy. Both the oviduct milieu and embryonic development are influenced by paracrine activity of follicular granulosa cells released at ovulation and remaining in suspension in the vicinity of the oocyte or embryo. These cells may amplify early pregnancy signals from a zygote to the endosalpinx. Beneficial effects of the oviduct on domestic animal embryos are contrasted with anomalies arising as a consequence of in vitro culture. Primate embryos do not require exposure to an oviduct for normal development, perhaps due to overlapping compositions of endosalpingeal and endometrial secretions. Additionally, primate endometrial secretions may be modified by viable gametes or an embryo in the presence of a cumulus cell suspension.

Temporal dynamics of ram sperm binding and survival during 48-h coculture with oviducal epithelial cells

Following insemination, ram spermatozoa bind to oviducal epithelial cells (OEC) in vivo and remain viable for several hours before fertilisation. In the present study, we investigated whether OEC monolayers reproduce this effect in vitro, performing an analysis of ram sperm binding and survival over an extended (48 h) period at 39°C. We wanted to determine whether the reproductive cycle phase and/or oviducal region would influence ram sperm binding and survival in coculture with OEC and whether reproductive and non-reproductive epithelial cells bound and maintained the viability of ram spermatozoa equivalently. Oviducts were separated into groups based on their ovarian state (follicular or luteal) and then divided into two parts (isthmus and ampulla) for OEC isolation. Sheep kidney epithelial cells (Madin-Darby ovine kidney; MDOK) were purchased commercially. Reproductive cycle phase, but not oviducal region, affected sperm binding to OEC. Although more spermatozoa bound to luteal OEC than to follicular OEC at 1 h, at 24 h follicular OEC had bound more spermatozoa than luteal OEC. Generally, spermatozoa that were bound to OEC and MDOK had enhanced viability at each of the time points investigated (1, 6, 24 and 48 h), but the viability of the OEC-bound spermatozoa was greater than that of the MDOK-bound spermatozoa at 48 h. In conclusion, ram sperm–epithelial cell interactions are temporal, dynamic and depend on the origin of the epithelial cells.

Sperm release from oviduct epithelial binding is controlled hormonally by peri-ovulatory graafian follicles

To avoid inappropriate conclusions being drawn from the extensive use of in vitro preparations of sperm-oviduct epithelial binding, it is recalled that events in the genital tract of mammals are regulated by the gonads, primarily by their changing secretion of steroid hormones. Key observations from in vivo models are used to emphasise the dynamic interactions between viable sperm cells and the caudal (distal) portion of the oviduct isthmus, the site of the functional sperm reservoir. These include (1) pre-ovulatory arrest and epithelial binding of intact sperm cells and thereby suppression of completion of capacitation, (2) peri-ovulatory activation and release from binding of discrete sub-populations of competent spermatozoa, and (3) post-ovulatory liberation of large numbers of spermatozoa. These observations underline the influence of endocrine regulation of sperm binding and release by peri-ovulatory Graafian follicles, a point brought out by the enhanced sperm release prompted by diverse treatments with solutions of progesterone. In the light of this evidence, the suitability of in vitro preparations for clarifying physiological events should be questioned, especially if myosalpingeal catecholamines diffusing out of the autonomic nervous system contribute to sperm activation and/or release. None of this is to infer that sperm cells themselves are without influence on their epithelial binding reaction(s). Nor is it to suggest that in vitro models of sperm-oviduct binding are without relevance to the development of sperm evaluation technologies. However, pre-ovulatory sperm-epithelial binding and a regulated peri-ovulatory release should be seen as vital tactics in the overall strategy of achieving successful monospermic fertilisation.

Spermatozoa stimulate prostaglandin synthesis and secretion in bovine oviductal epithelial cells

The dynamic action of oviductal secretory compounds on spermatozoa function is well documented. In contrast, the effect of spermatozoa on oviductal function remains poorly characterized. Previously, our lab and others have shown that prostaglandin (PG), together with other vasoactive peptides, plays major roles in oviductal contractions and sperm transport. We therefore examined the effect of spermatozoa on the production of PG by cow oviductal epithelial cells (OEC). A bovine spermatozoa–OEC co-culture system was utilized for this purpose. OECs in the second passage were co-cultured for 0, 1, 3, 6, 12, and 24 h with six doses of motile, killed, or truncated spermatozoa heads (control; without spermatozoa, 102–106spermatozoa/ml medium). The levels of PGE2and PGF2αin the medium were measured using enzyme immunoassays. Messenger RNA expression of cyclooxygenase-2, PGF synthase (PGFS), and PGE synthase (PGES) was investigated using real-time RT-PCR. The results indicated that motile spermatozoa increased the secretion of PG by OEC as well as cellular expression of mRNA for cyclooxygenase, PGES, and PGFS in a dose- and time-dependent manner. A maximum three- to fivefold increased secretion of PG was observed with a dose of 105spermatozoa/ml after a 12-h co-incubation. Neither killed spermatozoa nor truncated spermatozoa heads stimulated oviductal biosynthesis and secretion of PG at any dose or time point observed. The results provide the first evidence that live spermatozoa in the oviduct up-regulate the local PG system, and thereby, enhance oviductal contractions. Thus, spermatozoa may bear a role in accelerating their own transport into the fertilization site.

Mammalian embryo co-culture: Trials and tribulations of a misunderstood method

Embryo-somatic cell co-culture was devised over 40 years ago in an attempt to improve the development and viability of mammalian preimplantation embryos generated and cultured in vitro. While initial endeavours were successful in this respect, other studies soon highlighted a number of significant long-term detrimental impacts of this approach. Surprisingly little is known about the mechanisms underlying the beneficial effects of co-culture, although the production of embryotrophic compounds, modulation of nutrient profile, protection against culture-induced stress and/or toxin clearance are all contenders. The extent to which the inadvertent exposure of embryos to serum accounts for many of these effects remains open to question. Although the popularity of somatic cell co-culture has recently declined in favour of the use of sequential media due to concerns associated with its risk of disease transmission and long-term sequelae, we argue that complete dismissal of this technique is ill advised, given that our limited understanding of basic somatic cell interactions has prevented us from fully exploiting its potential. In this respect, there is some merit in focussing future research strategies based on reconstructed maternal tract tissue. Although the use of co-culture in clinical practice is unacceptable and its implementation in domestic species for commercial purposes should be viewed with diffidence, this technique can still provide a wealth of information on the development of novel, more physiological embryo in vitro culture systems. The proviso for acquiring such information is to gain a fuller understanding of the culture requirements/biochemistry of somatic cells and their interaction with the early conceptus.

Spermatozoa modulate epididymal cell proliferation and protein secretion in vitro

Normal epididymal function, such as protein expression and secretion, is primarily regulated by testicular androgens and temperature. However, the role of spermatozoa in this critical process has never been studied. In order to determine whether sperm itself could regulate epididymal function, we have developed a cell culture system of bovine epididymal cells to study the interactions between spermatozoa and the epididymal epithelium. Primary cells from caput, corpus, and cauda epididymal tissues were cultured in the presence of androgens at 32 degrees C (scrotal) and 37 degrees C (abdominal). Newly synthesized proteins were metabolically labeled with (35)S-methionine after sperm co-incubation and the pattern of secreted proteins was analyzed by two-dimensional polyacrylamide gel electrophoresis. Proliferation rate, protein secretion rate and electrophoretic patterns of secreted proteins were evaluated 48 hr post-co-incubation. Incubation at 32 degrees C indicated that spermatozoa stimulation increases the level of protein secretion of cultured cells from all epididymal sections while it slightly decreases proliferation of corpus cells. At 37 degrees C, spermatozoa co-incubation significantly decreases the protein secretion rate of cultured cells from all epididymal sections. Independently of cell incubation temperature, spermatozoa stimulation induces both an increase in the intensity of radiolabeled proteins and the appearance of new secreted proteins of caput cells without affecting the protein pattern of corpus or cauda cells. Incubation at 37 degrees C, however, greatly modifies the pattern of proteins expressed at 32 degrees C by cauda cells. Taken together, these results support the hypothesis that spermatozoa themselves affect epididymal cell function, most importantly for caput epididymides.

Gametes alter the oviductal secretory proteome

The mammalian oviduct provides an optimal environment for the maturation of gametes, fertilization, and early embryonic development. Secretory cells lining the lumen of the mammalian oviduct synthesize and secrete proteins that have been shown to interact with and influence the activities of gametes and embryos. We hypothesized that the presence of gametes in the oviduct alters the oviductal secretory proteomic profile. We used a combination of two-dimensional gel electrophoresis and liquid chromatography-tandem mass spectrometry to identify oviductal protein secretions that were altered in response to the presence of gametes in the oviduct. The oviductal response to spermatozoa was different from its response to oocytes as verified by Western blotting. The presence of spermatozoa or oocytes in the oviduct altered the secretion of specific proteins. Most of these proteins are known to have an influence on gamete maturation, viability, and function, and there is evidence to suggest these proteins may prepare the oviductal environment for arrival of the zygote. Our findings suggest the presence of a gamete recognition system within the oviduct capable of distinguishing between spermatozoa and oocytes.

Endometriosis affects sperm–endosalpingeal interactions

BACKGROUND

The interaction between spermatozoa and the epithelium of the isthmic region of the uterine tube is thought to be an important part of the mechanisms of sperm transport to the site of fertilization and in preparing them for fertilization. However, it is unclear whether a dysfunction of this mechanism may contribute to subfertility in some individuals.

METHODS

The sperm-binding characteristics of the epithelium from the uterine tubes of three groups of women were examined: (i) eight with pelvic endometriosis (not involving the uterine tubes); (ii) five women who had been receiving zoladex injections to control their symptoms; and (iii) as controls 10 women undergoing an elective procedure for benign gynaecological problems but with no other pathology of the reproductive tract.

RESULTS

Significantly more spermatozoa bound per unit area to the ampullary epithelium of the uterine tubes taken from women with a previous diagnosis of endometriosis.

CONCLUSIONS

These findings suggest that the characteristics of sperm binding to tubal epithelium may be disrupted in women with a gynaecological pathology such as endometriosis. It is suggested that this may have the potential to interfere with the availability of freely motile spermatozoa, of the appropriate physiological status, to take part in fertilization. This may be a newly described mechanism by which endometriosis can cause infertility.

Sperm-Induced Modification of the Oviductal Gene Expression Profile After Natural Insemination in Mice1

In mammals, the physiological interaction between spermatozoa and oviductal epithelia involves intimate and specific contact between the two cell types. Spermatozoa may undergo stringent selection processes within the female reproductive tract before they meet and fertilize oocytes. The physiological basis of the sperm selection process is largely unknown. Here we tested the hypothesis that the oviduct has a recognition system for spermatozoa that can detect the arrival of spermatozoa in the oviduct after insemination, resulting in alterations of the oviductal transcriptome. We initially performed a global screening of the oviductal transcriptome in mice 1) at the time of estrus (mating) and 2) 6 h after mating. Transcriptional alterations in the oviduct after mating were attributed to the presence of spermatozoa in the oviduct after mating and also to changes in the hormonal environment as female mice underwent the transition from estrus to diestrus. To distinguish these possibilities, female mice were then mated with T145H mutant mice, which because of spermatogenic arrest, produce seminal plasma but no spermatozoa. Focusing on two molecules that in the first experiment were upregulated after mating, it was found that adrenomedullin and prostaglandin endoperoxidase synthase 2 transcripts were upregulated in the oviducts of mice only after mating with fertile males; those mated with T145H infertile males showed significantly less response. These results indicate that it is the arrival of spermatozoa in the oviduct that activates one or more signal transduction pathways and leads to changes in the oviductal transcriptome profiles.

Reflections upon sperm-endosalpingeal and sperm-zona pellucida interactions in vivo and in vitro

In terms of experimental studies of the process of fertilization in mammals, this essay attempts to give a balanced assessment of current interpretations and to raise questions of direct relevance to two fields of research. First, the nature of pre-ovulatory sperm-endosalpingeal binding is set in a physiological perspective, and examination of this dynamic process in vitro is shown to suffer from serious shortcomings. In particular, sperm-epithelial binding reactions demonstrated in cultures of endosalpingeal cells may represent only a portion of the binding reaction in vivo or, as revealed by sperm binding to the tracheal epithelium, could be largely non-specific. Second, concerning the subsequent phase of binding of a fertilizing spermatozoon to the zona pellucida, the nature of the initial contact arrest of the sperm head is evaluated, especially in the light of the highly uneven or 'pitted' surface of this outer coating of the oocyte. Bearing in mind the active phase of oviduct macromolecular secretion that continues after ovulation, the question is posed as to how functional sperm binding sites are preserved on the surface of the zona pellucida rather than masked by epithelial and cumulus cell secretions. Finally, it is recalled that initial sperm : egg ratios at the site of fertilization in the ampullary-isthmic region of the oviduct are close to unity in diverse species of mammal, such fertilizing spermatozoa being released from prominent reserves in the caudal isthmus shortly before the time of ovulation. On strictly quantitative grounds, therefore, the extent to which biochemical or molecular studies portray changes in the vanguard of fertilizing spermatozoa needs to be questioned. Such studies are more likely to be descriptive of overall changes in very large numbers of sperm cells at diverse stages of maturation.

Capacitation of mammalian spermatozoa in vivo, with a specific focus on events in the fallopian tubes

This essay argues strongly that for those sperm cells involved in fertilisation, the process of capacitation represents an active and specific coordination within succeeding regions of the female tract and one whose completion is synchronised with the events of ovulation. Observations on the time-course of capacitation when spermatozoa are first exposed to the uterus and then progress to the Fallopian tubes indicate a synergistic influence of these adjoining portions of the female tract on the rate of capacitation. Three concepts on the control of capacitation are introduced to emphasise the importance of integration in vivo, namely that (1) completion of capacitation is a peri-ovulatory event, (2) suppression of completion of capacitation is an essential storage strategy during a long pre-ovulatory interval, and (3) the process of capacitation comes under the influence of local and systemic ovarian control mechanisms, especially the secretion of progesterone from Graafian follicles soon to ovulate. The last would act to coordinate the final maturation and meeting of male and female gametes. Despite the preceding points, the requirement for such integrated in vivo programming of sperm cell maturation can clearly be overridden in systems of culture. The most reasonable interpretation here would be that a microdrop of culture medium containing eggs, follicular cells and components of follicular fluid would to a considerable extent represent a post-ovulatory environment. Within such a preparation, there would be leaching of the sperm surface among the relatively vast and heterogeneous population of cells, and a proportion of spermatozoa could then respond to 'post-ovulatory signals', not least to molecular influences of the zona pellucida and vitelline products for completion of capacitation. Nonetheless, a physiologically meaningful interpretation of capacitation calls for a stepwise analysis of the dynamic interactions between sperm cell and female tract at successive stages between the uterus and ampullary-isthmic junction.

Physiology of gamete and embryo transport through the fallopian tube

A great deal is now known about the migration of spermatozoa within the female reproductive tract, and how they interact with the oocyte and achieve fertilization in a variety of species. The process involves a series of complex features. It is a mixture of active and passive transport and active migration, with drastic jumps in the numbers of spermatozoa that migrate beyond specific physiological checkpoints, and with interactions occurring between spermatozoa, epithelium and luminal fluid. A reservoir of spermatozoa forms, at a discrete location, to hold and liberate spermatozoa in a gradual fashion. After fertilization has occurred, zygotes are passively transported to the uterus by a series of closely coordinated mechanical events where activities of cilia and smooth muscle predominate. Passage of the embryo from oviduct to uterus is regulated and timed by ovarian hormones, signals associated with mating, and zygotic substances. The diverse and exquisite patterns and regulatory signals typical of sperm migration and ovum transport across many species provide fascinating examples of adaptations according with differing reproductive strategies in various mammals.

First identification of caldesmon transcripts in bovine oviduct epithelial cells in vitro by means of an RNA differential display technique examining culture-induced expression changes

Innovative molecular biology techniques enable the quick evaluation of distinct gene expression pattern of cells or tissues. Hitherto, a cell-type-specific behaviour has been difficult to evaluate. In addition to standard morphological and immunological criteria in this study the expression of in vitro-cultured bovine oviduct epithelial cells (BOECs) was compared with fresh cells by RNA arbitrarily primed polymerase chain reaction (RAP-PCR). The cultured cells showed mitotic activity during the whole culture period (6 days) until they had reached about 80% confluency. Remarkable results of a random transcript screening using fresh versus cultured BOECs were reported, in which a single PCR product appeared during culture, but was absent in fresh cells. Sequence analysis of the culture-induced 522 bp fragment revealed a high homology (87%) to caldesmon (CaD) of various species and a 92% homology to a short cDNA fragment of a bovine non-muscle CaD. Specific, cross-species PCR primers were used to elongate this partial sequence (1,036 bp). This resulting cDNA showed an open reading frame and was identified as a bovine non-muscle CaD isoform. When compared with human non-muscle CaDs (89% homology) a deletion of 2 codons was observed. According to sequential culture experiments, CaD expression was not found in fresh BOECs but specific transcripts appeared within 48-113 h under specific culture conditions. It is likely that augmented CaD expression in cultured BOECs may reflect the cell effort adapting to specific culture conditions. The hypothesis that increased CaD levels could be important to facilitate adherence and spreading by formation of new stress fibres can be favoured. This first identification of caldesmon expression being specifically induced during in vitro culture demonstrates the potential of RAP-PCR for the analysis and validation of cell culture techniques.

In vitro interactions of cryopreserved stallion spermatozoa and oviduct (uterine tube) epithelial cells or their secretory products

Formation of a spermatozoa ('sperm') reservoir in the mare is thought to occur through lectin-mediated sperm attachment to the oviductal epithelium. Once attached, prefertilization sperm survival is supported by oviductal factors. Cryopreservation of stallion sperm decreases the number of sperm attaching to oviduct epithelial cells (OEC) and the length of time these sperm survive. Quantification of in vitro interactions between sperm and OEC in a co-culture system may provide an assay for functional integrity of cryopreserved or fresh sperm samples. Additionally, superior additives for in vitro handling of stallion sperm may be isolated from OEC secretory products. Experiment 1 compared first service conception (FSC) rates resulting from the use of cryopreserved sperm of seven stallions, with sperm function in co-culture such as attachment to OEC and subsequent survival time. Stallions were grouped by cumulative FSC rates observed over three seasons as having average (44 +/- 3%) or high (65 +/- 2%) fertility over a total of 217 first services (31 +/- 9 per stallion). Samples from stallions in the high fertility group had more (P = 0.04) sperm attached to OEC and longer subsequent sperm survival in co-culture (P = 0.05) as compared with those from the average fertility group. FSC rates correlated with numbers of sperm attaching to OEC and their survival time in co-culture (r > or = 0.71). In Experiment 2, the function of cryopreserved stallion sperm was evaluated in culture with OEC secretory products from three different sources. After 5 h of culture, sperm incubated with medium conditioned by bovine OEC which had been 'bioactivated' (e.g. previously exposed to sperm in culture) were found to be more (P < or = 0.05) motile and capacitated as compared to sperm in basal TALP medium alone. Sperm in this conditioned medium also survived longer (P = 0.05; 27 +/- 5 h vs. 17 +/- 4 h) than did those in control medium.

Steroid regulation of retinol-binding protein in the ovine oviduct

Two studies were conducted to identify retinol-binding protein (RBP) expression in the ovine oviduct and to determine the role of ovarian steroids in its regulation. Ewes were salpingectomized on Days 1, 5, or 10 of their respective estrous cycles, and oviducts were homogenized for RNA analysis, fixed for immunocytochemistry (ICC), or cultured for 24 h for protein analysis. ICC localized RBP to the epithelium of all oviducts. RBP synthesis was demonstrated by immunoprecipitation of radiolabeled RBP from the medium of oviductal explant cultures. Explant culture medium from oviducts harvested on Day 1 contained significantly more RBP than medium from oviducts collected on Days 5 or 10. Slot-blot analysis demonstrated that steady-state RBP mRNA levels were significantly higher on Day 1 than Day 5 or 10. In the second experiment, ovariectomized ewes were treated with estradiol-17beta (E2), progesterone (P4), E2+P4 (E2+P4), or vehicle control, and oviducts were analyzed as above. P4 alone or in combination with E2 significantly reduced steady-state RBP mRNA levels compared to those in E2-treated animals. Oviductal explants from E2- and E2+P4-treated animals released 3- to 5-fold more RBP into the medium than control and P4 treatments as determined by ELISA. RBP synthesis of metabolically labeled RBP was increased by E2 and E2+P4 treatments. This study demonstrates that P4 applied on an estradiol background negatively regulates RBP gene expression in the oviduct whereas estradiol appears to stimulate RBP synthesis and secretion.

Coculture of human sperm with bovine oviduct epithelial cells decreases sperm chromatin structural changes seen during culture in media alone

OBJECTIVE

To compare sperm chromatin structural changes seen in media only culture or in coculture with bovine oviduct epithelial cells.

DESIGN

Three freshly ejaculated and three cryopreserved sperm samples in media culture or in oviduct epithelial cell coculture. Sperm in each treatment were evaluated by the sperm chromatin structure assay during a 72-hour time course.

SETTING

An academic research laboratory.

PATIENT(S)

Normospermic donors with children.

INTERVENTION(S)

Semen collection through masturbation after 48 hours of abstinence.

MAIN OUTCOME MEASURE(S)

The sperm chromatin structure assay using flow cytometry to detect the susceptibility of sperm in either treatment to denaturation of DNA in situ.

RESULT(S)

The sperm chromatin structure assay data differed for sperm type (fresh or cryopreserved), over time, and between treatments within 6 hours of culture. In oviduct epithelial cell coculture, fresh sperm chromatin structure assay values for fresh sperm were stable, whereas in control medium higher chromatin degeneration levels were seen by 10 hours. For cryopreserved sperm, chromatin degeneration had increased by 1 hour postthaw in both treatments, although levels were higher in the control treatment thereafter.

CONCLUSION(S)

Sperm chromatin structural changes occur over time in culture. Such changes were observed within 2 hours for cryopreserved sperm. Coculture of sperm with oviduct epithelial cells results in a stabilizing effect for sperm against chromatin changes.

Effects of platelet-derived growth factor (PDGF) on the in vitro production of bovine embryos in protein-free media

The purpose of our experiments was to explore the effects of platelet-derived growth factor (PDGF)-supplementation at the various steps of in vitro production of bovine embryos using protein-free media. Cumulus-oocyte-complexes (COC) were collected by slicing abattoir ovaries and then dividing the COC into 2 morphological categories. After maturation for 24 h in TCM-199 supplemented with hormones and either 20% estrous cow serum (ECS) or 1 mg/ml polyvinyl-alcohol (PVA), oocytes were co-incubated for 19 h with frozen/thawed spermatozoa from bull of proven fertility. The semen was diluted in Fert-Talp supplemented with heparin, hypotaurine and epinephrine and either 6 mg/ml bovine serum albumin (BSA) or 1 mg/ml PVA. Presumptive zygotes were transferred into embryo culture medium containing either 20% ECS or 1 mg/ml PVA for a total of 10 d. The PDGF was added at concentrations of 1, 10 or 100 ng/ml to the maturation medium (Experiment 1), fertilization medium (Experiment 2) or culture medium from Day 1 on (Experiment 3), respectively, or at 1 ng/ml PDGF to both the fertilization and culture medium from Day 3 on (Experiment 4), with each medium supplemented with PVA. Oocytes/embryos incubated in the absence of PDGF in media supplemented with either ECS or PVA served as controls. An average of 20 COC was incubated in 1 droplet under silicone oil, and each experiment contained 4 to 6 replicates. No significant differences were found among the various concentrations of PDGF, nor did PDGF-supplementation during maturation (Experiment 1) or embryo culture on Day 1 (Experiment 3) significantly affect development of oocytes/embryos (34.7 +/- 3.5 to 40.4 +/- 2.5% morulae, 11.9 +/- 2.4 to 18.8 +/- 2.5% blastocysts; and 23.2 +/- 2.3 to 27.5 +/- 3.4% morulae, 11.5 +/- 2.6 to 12.7 +/- 2.3% blastocysts, respectively; x +/- SEM). In the presence of 10 ng/ml PDGF in the fertilization medium development to morulae and blastocysts was similar to that of the ECS-group, and was higher (P < 0.05) than that of the PVA-control (ECS: 32.1 +/- 4.6 and 13.8 +/- 2.7%; PVA: 17.5 +/- 0.8 and 6.1 +/- 1.3%; PDGF: 30.6 +/- 3.0 and 14.0 +/- 2.2%, respectively). Development to morulae/blastocysts was increased, and was at the same level as in the ECS-group when the fertilization and/or embryo culture medium on Day 3 contained PDGF compared with the PVA-control group (morulae: ECS 25.3 +/- 4.4%, PVA 13.9 +/- 2.2% [P < 0.05], PDGF 16.7 +/- 3.2 to 19.1 +/- 1.1%; blastocysts: ECS 5.3 +/- 2.1%, PVA 5.0 +/- 1.7%, PDGF 7.1 +/- 1.6 to 9.1 +/- 1.7%, respectively). These results indicate that under our laboratory conditions PDGF can elevate low rates of development and the addition of PDGF to the fertilization medium enhances bovine preimplantation embryonic development. Thus, PDGF can be potentially an important factor in a completely defined medium to substitute the effects of serum.

Regional differences in uteroglobin biosynthesis along the rabbit oviduct: immunohistochemical and biochemical studies

The biosynthesis of uteroglobin in three regions of the rabbit oviduct was assessed by means of immunocytochemical studies, radioimmunoassay measurements of the protein, and quantitative determinations of its mRNA. Immunocytochemical observations suggested that the number of immunopositive cells and the intensity of their immunolabelling were similar in the distal (infundibular) and the middle regions. In contrast, the isthmic portion appeared to contain less positive cells and weaker immunolabelling. In agreement with these findings, biochemical studies demonstrated that the tissue contents of uteroglobin and its mRNA were similar in the distal and the middle regions whereas the concentrations of both were about three-to four-fold lower in the isthmic portion. The results are discussed in relation to a possible role for uteroglobin in maintaining appropriate environmental conditions for the gametes and the early embryo.

Cytofluorescent assay to quantify adhesion of equine spermatozoa to oviduct epithelial cells in vitro

To facilitate the study of interactions between equine spermatozoa and homologous oviduct epithelial cells, we developed an assay to count labelled spermatozoa bound to oviduct epithelial cell (OEC) monolayers and used the assay to compare the binding ability of spermatozoa from different stallions. Washed spermatozoa from three stallions were incubated with the fluorochrome Hoechst 33342 (5 micrograms/ml) for 1 min. Spermatozoa were then layered over confluent monolayers of oviduct epithelial cells in 2 cm2 culture wells. Coculture treatments comprised five concentrations of spermatozoa (10(5), 5 x 10(5), 10(6), 2.5 x 10(6), and 5 x 10(6) per well). Cocultures were incubated for 30 min before unattached spermatozoa were aspirated in coculture supernatant. Fluorescent videoimages of attached spermatozoa were digitized, and attached spermatozoa were counted by image processing and analysis. Four wells (replicates) of each concentration were allocated within each ejaculate, and ejaculates were blocked by stallion for ANOVA. The total number of spermatozoa bound was not different between replicate wells (P > 0.1). Stallion, ejaculate, concentration, and all higher level interactions influenced total spermatozoa bound (P < 0.00001). Coefficients of variation between replicates were lowest for inseminate concentrations between 10(6) and 5 x 10(6) spermatozoa per well. Within the ejaculate, a log linear relationship exists between the number of bound spermatozoa and a spermatozoal concentration of the inseminate between 5 x 10(5) and 5 x 10(6) spermatozoa per well. This assay provides a reliable method of determining numbers of spermatozoa bound to somatic cells in vitro. Furthermore, differences exist in the ability of spermatozoa from different stallions to bind OEC monolayers.

Functions of proteins secreted by oviduct epithelial cells

Studies on embryonic development in vitro as well as observations in vivo, suggested that two aspects of oviduct physiology are important for early development. On one side has to be considered the oviduct "environment": temperature, pH, osmotic pressure, nutrients, oxygen tension, free radical scavengers, etc. On the other, the oviduct "active components": stimulatory and/or regulatory molecules, supposed to finely regulate the fertilisation process and the first differentiative steps. While the physical environment of the oviduct has been under investigation for some decades, studies on oviduct-specific molecules and their functions have only been developed much more recently. The amount of information on this topic, however, has rapidly reached the size that demands a summary. In this review the descriptive literature on oviduct specific proteins will be examined as a basis for illustrating the possible functions of these molecules. In particular their role in fertilisation and early embryonic cleavages will be analysed in some details. Finally a section is devoted to the presence and physiological significance of growth factors in oviduct fluid.

Isolation, cell culture, and characterization of oviduct epithelial cells of the cow

This report describes an easy method of isolation and cell culture of the epithelial cells of cow oviduct. Incubation of cow oviduct with 0.1 mg/ml collagenase in the lumen for 90 minutes helped to dislodge large numbers of ciliated and secretory epithelial cells. The isolated cells, when seeded on plastic, proliferated very quickly and became confluent in 8-10 days in 35 mm Petri dishes. The isolated ciliated cells which attached to the plastic dish lost their cilia after 4-5 days in culture. The cultured epithelial cells were keretin positive. The isolated bovine oviduct epithelial cells, when cultured on plastic precoated with 10 mg/ml matrigel, organized themselves into hollow tubes or spheres with microvilli directed towards the lumen. The epithelial cells seeded on 2 mg/ml matrigel became subconfluent in 15-20 days after seeding. The histoarchitecture of the secretory cells growing in vitro on matrigel resembled that of intact oviduct secretory epithelial cells. Occasional ciliated cells containing large number of mitochondria were observed in the monolayer cultured on 2 mg/ml matrigel substratum but possessed few cilia. The oviduct epithelial cells cultured on 2 mg/ml matrigel incorporated 35S-methionine linearly into protein up to 8 hours in the presence of estradiol or progesterone. The fluorograph of the newly synthesized proteins indicated the presence of an additional 60 kd protein in the cell extract of epithelial cells incubated with estradiol.

Isolation, culture, and characterization of equine oviduct epithelial cells in vitro

Oviduct epithelial cells (OEC) increasingly are used to support embryonic development and to study gamete interactions with the female reproductive tract in vitro. This series of experiments was designed to characterize monolayers derived from oviduct epithelium. Epithelial cells harvested from the isthmus and ampulla of the oviducts of five estrous mares were cultured with or without the basal lamina extract, Matrigel. Within each group OEC were cultured in the presence of either estradiol-17 beta or a carrier control. All groups were subcultured three times. Epithelial cell morphology and function were examined by microscopy, analysis of secreted proteins, and immunocytochemistry. Epithelial cells attached more rapidly and reached confluence sooner when cultured on Matrigel than in uncoated wells. Cells showed variable evidence of ciliary activity up to 12 days in primary culture. Cells grown on Matrigel had a more polarized appearance in primary culture than those in uncoated wells, although no morphologic difference between anatomic site of origin or between steroid treated groups was noted. Anatomic site of origin had no effect, and steroid treatment had minimal effects, on patterns of secreted proteins. However, some differences were noted in protein secretion between cells grown with or without Matrigel. These data suggest that culture substrate may affect structure and function of OEC monolayers.

Effect of coculturing spermatozoa with oviductal cells on the incidence of polyspermy in pig in vitro fertilization

It is known that oviductal cells play an important role in fertilization in vivo. We were interested in the effect of those cells on spermatozoa and their influence on the incidence of polyspermy in pig in vitro fertilization (IVF) when cocultured with spermatozoa. Oviductal cells are believed to select a highly fecund population of spermatozoa. By coculturing spermatozoa with oviductal cells it is possible to reduce the number of spermatozoa confronting the eggs at fertilization, reducing the incidence of polyspermy. In our study, spermatozoa were cocultured with oviductal cells for 30 min so that they could bind to the oviductal cells. Both bound and unbound spermatozoa were used for fertilization. The results show that the spermatozoa that were bound to the oviductal cells were capable of fertilizing the eggs, but the nonbound spermatozoa had a reduced penetration incidence. With the bound sperm, polyspermy incidence decreased and the two-pronuclei proportion increased. We also found that with time the spermatozoa released from the cells had better motility than those that did not bind. Therefore, it is our belief that oviductal cells can be used for porcine IVF resulting in a lower polyspermy incidence and higher pronuclei incidence.

In vitro maturation, fertilization and culture to blastocysts of bovine oocytes in protein-free media

This study examined the role of protein supplementation at the various steps of the in vitro production of bovine embryos derived from two different morphological categories of COC. The basic medium was TCM 199 and was supplemented with hormones during maturation in vitro and either estrous cow serum (ECS), bovine serum albumin (BSA) at various concentrations or polyvinyl-alcohol (PVA). Fertilization in vitro was carried out using frozen-thawed semen or one bull in Fert-talp containing heparin, hypotaurin and epinephrine and either 6 mg/ml BSA or 1 mg/ml PVA. In vitro culture up to the blastocyst stage was performed in TCM 199 supplemented with either ECS, BSA or PVA. The first experiment investigated the influence of different medium-supplements (ECS, BSA or PVA) on nuclear maturation and revealed no significant differences among treatment groups nor between categories of COC (63.9% to 74.9% and 48.9% to 77.0%, respectively). The time course of in vitro fertilization was elucidated in Experiment 2 in medium supplemented with either protein or PVA during maturation and fertilization. Penetration was not affected (70.9% to 79.3% penetration 12 h after onset of oocyte-sperm-co-incubation), but formation of pronuclei was decreased (P < 0.05) 12 and 19 h after onset of oocyte-sperm-co-incubation and was retarded in medium supplemented with PVA (12 h: 63.8 vs 21.4 %; 19 h: 57.5 vs 20.8 %, respectively) while cleavage was not affected. In Experiment 3, six treatment groups were formed in which the two different morphological categories of cumulus-oocyte-complexes (COC) were incubated in basic medium supplemented with 1) ECS during maturation and embryo culture and BSA during fertilization; 2) PVA during maturation and embryo culture, fertilization medium with PVA; 3) PVA during maturation and embryo culture, fertilization medium with BSA; 4) BSA (1 mg/ml) during maturation, fertilization and embryo culture; 5) BSA (6 mg/ml) during maturation, fertilization and embryo culture; and 6) BSA (10 mg/ml) during maturation, fertilization and embryo culture. The rates of cleavage and the development to morulae or blastocysts did not differ (P > 0.05) among treatment groups and between both categories of COC and were showing a high degree of variability (cleavage 54.0% to 65.1% and 41.3% to 55.7%, respectively; morulae 25.3% to 53.0% and 26.0% to 51.2%, respectively; blastocysts 5.4% to 24.7% and 0.6% to 20.3%, respectively). Parthenogenetic activation only rarely occurred in medium containing PVA throughout all steps of in vitro production of bovine embryos (Experiment 4) and led to early cleavage stages (8%), but no development to morula- or blastocyst-stages was observed. It is concluded that 1) formation of pronuclei was retarded in medium lacking protein-supplementation, indicating that BSA is required for regular fertilization in vitro and 2) under our experimental conditions, protein-supplementation is not necessary for maturation and development up to the blastocyst stage in vitro.