Effect of growth hormone (GH) on in vitro nuclear and cytoplasmic oocyte maturation, cumulus expansion, hyaluronan synthases, and connexins 32 and 43 expression, and GH receptor messenger RNA expression in equine and porcine species

The effect of bovine embryo culture without proteins supplements until day 4 on transcription level of hyaluronan synthases, receptors and mtDNA content

The effect of bovine embryo culture on a flat surface, (without a surface-active compound) on the level of mRNA expression of hyaluronan (HA) synthases (Has1, Has2 and Has3), Ha receptors RHAMM and C44 receptors was evaluated by mitochondrial DNA concentration and in vitro development. Cultures were evaluated up to 96 h post-insemination (hpi) using SOFaa medium. Of the three Has isoforms, Has2 expression only increased in the bovine serum albumin (BSA)-only supplemented groups regardless of time of BSA addition. Expression of RHAMM receptors was highly dependent on the addition of HA, irrespective of the presence of BSA in the medium. In contrast, expression of the CD44 receptor gene was not affected by any treatment. The cleavage rates and number of embryos that developed to <or=8-cell stage by day 4 were not affected by lack of BSA in the medium, but increased numbers of blastocysts developed in medium supplemented with BSA from days 1 or 4 with or without HA than in medium that had HA only. Addition of both HA and BSA at day 4 increased mtDNA copy numbers at the blastocyst stage. Data suggest that the addition of BSA and/or HA at 96 hpi increased expression of RHAMM and Has2 genes, but not CD44, Has1 or Has3 genes. Higher expression levels of Has2 than Has1 and the three isoforms indicate that high- rather than low-molecular-weight HA should be used for preimplantation bovine embryo culture.

New insights into the mechanisms of fertilization: comparison of the fertilization steps, composition, and structure of the zona pellucida between horses and pigs

The mechanism of fertilization remains largely enigmatic in mammals. Most studies exploring the molecular mechanism underlying fertilization have been restricted to a single species, generally the mouse, without a comparative approach. However, the identification of divergences between species could allow us to highlight key components in the mechanism of fertilization. In the pig, in vitro fertilization (IVF) and polyspermy rates are high, and spermatozoa penetrate easily through the zona pellucida (ZP). In contrast, IVF rates are low in the horse, and polyspermy is scarce. Our objective was to develop a comparative strategy between these two divergent models. First, we compared the role of equine and porcine gametes in the following five functions using intraspecific and interspecific IVF: ZP binding, acrosome reaction, penetration through the ZP, gamete fusion, and pronucleus formation. Under in vitro conditions, we showed that the ZP is a determining element in sperm-ZP attachment and penetration, whereas the capacity of the spermatozoa is of less importance. In contrast, the capacity of the spermatozoa is a key component of the acrosome reaction step. Second, we compared the composition and structure of the equine and porcine ZP. We observed differences in the number and localization of the ZP glycoproteins and in the mesh-like structure of the ZP between equine and porcine species. These differences might correlate with the differences in spermatozoal attachment and penetration rates. In conclusion, our comparative approach allows us to identify determining elements in the mechanism of fertilization.

The extracellular calcium-sensing receptor is expressed in the cumulus-oocyte complex in mammals and modulates oocyte meiotic maturation

The extracellular calcium-sensing receptor (CASR) plays an important role in cells involved in calcium (Ca2+) homeostasis by directly sensing changes in the extracellular Ca2+ ion concentration. We previously reported the localization and quantitative expression of CASR protein in human oocytes. In this study, we examined the expression and the functional role of CASR during oocyte meiotic maturation in a large mammal animal model, the horse. As in humans, CASR protein was found to be expressed in equine oocytes and cumulus cells. Western-blot analysis revealed a single 130 kDa band in denuded oocytes and a doublet of 130-120 kDa in cumulus cells. CASR labeling was observed by confocal microscopy in cumulus cells and in oocytes on the plasma membrane and within the cytoplasm at all examined stages of meiosis. Functionally, the CASR allosteric effector NPS R-467, in the presence of 2.92 mM external Ca2+, increased oocyte maturation rate in a dose-dependent manner and its stimulatory effect was attenuated by pre-treatment with the CASR antagonist NPS 2390. NPS R-467 had no effect in suboptimal external Ca2+ (0.5 mM), indicating that it requires higher external Ca2+ to promote oocyte maturation. In oocytes treated with NPS R-467, CASR staining increased at the plasmalemma and was reduced in the cytosol. Moreover, NPS R-467 increased the activity of MAPK, also called ERK, in cumulus cells and oocytes. These results provide evidence of a novel signal transduction pathway modulating oocyte meiotic maturation in mammals in addition to the well-known systemic hormones.

Protective effects of the cumulus-corona radiata complex during vitrification of horse oocytes

Vitrifying oocytes is a potentially valuable means of preserving the female germ line, but significantly compromises oocyte developmental competence. This study examined the hypothesis that the cumulus complex protects the oocyte during vitrification. Vitrified-warmed immature cumulus oocyte complexes (COCs) were labelled with a plasma membrane impermeant DNA marker (ethidium homodimer-1) to examine the percentage and location of dead cumulus cells, and to investigate the effect of the proportion of dead cells (+1,+2 or +3) on the success of in vitro maturation (IVM). Further, oocytes were labelled for connexin-43 or injected with Lucifer yellow dye to determine whether the integrity of the gap junctions between an oocyte and its cumulus was compromised by vitrification. Finally, the effect of denuding immature and mature oocytes on their ability to withstand vitrification was examined. Cryopreserving immature COCs increased the number of dead cumulus cells (13 vs 2.6% for controls; P<0.05). However, an increased proportion of dead cumulus cells did not affect post-warming maturation rates (∼30% MII) presumably because dead cells were located at the periphery of the cumulus mass and cumulus-oocyte gap junction communication was not disrupted. Moreover, cumulus removal prior to IVM or vitrification indicated that while the cumulus does protect immature oocytes during vitrification it does so by mechanisms other than support during maturation. Cumulus presence was also found to protect mature equine oocytes against vitrification-induced damage since cumulus-enclosed MII oocytes preserved their meiotic spindle quality better during vitrification than denuded oocytes (38.1 vs 3.1% normal spindles; P<0.05).

Growth hormone pathway gene expression varies in porcine cumulus-oocyte complexes during in vitro maturation

Growth hormone (GH) plays important roles in oocyte development and facilitates the successful production of competent oocytes in many species both in vivo and in vitro. However, the mechanism of GH action on oocyte maturation is not well known. In this paper, the temporospatial messenger ribonucleic acid expression patterns of GH and several other GH-related factors were quantitatively analyzed in porcine cumulus-oocytes complex throughout in vitro maturation (IVM). GH expression was decreased in oocytes during IVM while absent in cumulus cells. GH receptor, insulin-like growth factor-1 (IGF-1), and IGF-1 receptor expressions were also downregulated in oocytes. In cumulus cells, the expression of IGF-1 decreased significantly while IGF-1 receptor expression remained constant. The transcripts of Janus kinase 2 increased in both oocytes and cumulus cells during IVM. The current precise gene expression information provides further evidence to explain the complex network of GH signaling involved in IVM of porcine oocyte.

Growth hormone and in vitro maturation of rhesus macaque oocytes and subsequent embryo development

PURPOSE

The objective of this study was to use a nonhuman primate model to examine the effects of growth hormone (GH) on oocyte in vitro maturation (IVM).

METHODS

Immunocytochemistry confirmed the presence of GH receptors in rhesus cumulus oocyte complexes and the cytoplasm of embryonic blastomeres. Recombinant human GH (r-hGH) was added to IVM medium and cumulus expansion, nuclear maturation, cytoplasmic maturation and embryo development were analyzed.

RESULTS

Cumulus expansion was highest in the presence of 1 and 10 ng/ml r-hGH. The addition of r-hGH during IVM increased the percentage of embryos progressing to at least the 9-16 cell stage. In a separate study, 100 ng/ml r-hGH was supplemented to IVM and embryo culture medium and no effect was observed.

CONCLUSIONS

The presence of GH receptors along with increased cumulus expansion and embryos progressing to the 9-16 cell stage supports the hypothesis that r-hGH may be involved in oocyte maturation.

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

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

Reduction of connexin 43 in human cumulus cells yields good embryo competence during ICSI

PURPOSE

The purpose of this study was to predict developmental competence of human oocytes during ICSI via analysis of connexin 43 (Cx43) in cumulus cells surrounding mature oocytes.

MATERIALS AND METHODS

Human cumulus cells were manually separated from the oocyte-cumulus complex under a microscope. Cx43 mRNA was expressed by real-time quantitative polymerase chain reaction (RT-PCR) measurement in cumulus cells.

RESULTS

There was no significant relationship between expression of Cx43 and fertilisation or cleavage rate. However, Cx43 expression was lower in the good morphology group (blastomeres>7 cells with fragmentation<10% on day 3) when compared to the other groups (p=0.035).

CONCLUSIONS

These results suggest that full reduction of Cx43 expression on cumulus cells at the time of oocyte collection during ICSI is essential for developmental competence of human oocytes.

Inhibition of boar sperm hyaluronidase activity by tannic acid reduces polyspermy during in vitro fertilization of porcine oocytes

The present study was conducted to examine the effects of three polyphenols (tannic acid, apigenin and quercetin) on hyaluronidase activity and in vitro fertilization (IVF) parameters. Among them, tannic acid showed by far the strongest potency for blocking hyaluronidase activity extracted from preincubated boar sperm, causing a dose-dependent inhibition over the range of 2–10 μg/ml. When cumulus-intact and cumulus-free oocytes were inseminated in IVF medium containing tannic acid, the penetration and the polyspermy rates were significantly decreased in the presence of 10 μg/ml tannic acid compared with those in the absence of tannic acid, and the addition of 5 μg/ml tannic acid significantly reduced the polyspermy rate (p < 0.05) compared with that of the control while maintaining the high penetration rate. However, apigenin and quercetin had no effect on the rate of polyspermy. Interestingly, the incidence of polyspermy was significantly reduced in oocytes inseminated with sperm pretreated with 5 μg/ml tannic acid (p < 0.05), although the pretreatment of oocytes had no effect against the polyspermy after insemination with untreated sperm. Treatment with tannic acid caused neither a protective proteolytic modification of the zona pellucida matrix before fertilization, nor a reduction of the proteolytic activity of acrosomal contents or the number of zona-bound spermatozoa. These data suggest that an appropriate concentration of tannic acid prevents polyspermy through the inhibition of sperm hyaluronidase activity during IVF of porcine oocytes.

Control of reproductive processes by growth hormone: extra- and intracellular mechanisms

Recent data on the association between growth hormone (GH) and male and female reproductive processes, as well as the effects of GH on these processes and on some reproductive and non-reproductive disorders, and possible extra- and intracellular mediators of its action are reviewed. The available data suggest that GH is an important endocrine and autocrine/paracrine regulator of reproduction. It controls proliferation, apoptosis, growth and differentiation and the secretory and generative activities of different reproductive organs. It also regulates their response to gonadotrophin-releasing hormone (GnRH) and gonadotropins. Despite the effects of GH on the IGF/IGFBP (insulin-like growth factor binding protein) system, oxytocin, steroids, activin, gonadotropin and gonadotropin receptors, the majority of GH's actions on the reproductive processes are probably mediated not by these substances but by specific GH receptors acting through cAMP/protein kinase A, protein kinase G, tyrosine kinase-, MAP kinase and CDC2 kinase-dependent intracellular mechanisms. Although GH treatments can increase the risk of some reproductive and non-reproductive disorders, they may be useful in improving gonadal function, inducing superovulation and in embryo production.

In vivo effect of growth hormone on the expression of connexin-43 in bovine ovarian follicles

This study assessed the in vivo effects of recombinant growth hormone (rGH) administration on the expression of connexin-43 (Cx43) in bovine ovarian follicles. Two independent experiments were carried out using either estrous unsynchronized or synchronized multiparous Aberdeen Angus cows. rGH-treated animals were inoculated with a single dose of hormone (500 mg, intramuscular) while control animals were inoculated with hormone diluent. Five and 14 days after treatment (Experiments 1 and 2, respectively), ovarian Cx43 and apoptosis expression were assessed using immunohistochemistry. In both experiments primary, secondary, and tertiary follicles from rGH-treated and control groups distinctly expressed Cx43 protein. Primordial and atretic follicles were Cx43-negative. Interestingly, the number of Cx43 dots per granulosa cell did not show significant variation at different folliculogenesis stages neither in the rGH-treated nor in the control group. In unsynchronized animals, Cx43-positive follicles per total number of follicles ratio showed an interaction between stage of folliculogenesis and treatment due to significant differences between treatment groups in the early secondary follicle stage. In synchronized animals, there were significant differences between treatment groups and folliculogenesis stage. In both experiments, atretic follicles showed apoptosis-related DNA-fragmentation as determined by terminal uridin nick end labeling (TUNEL) assay. Tertiary follicles presented moderate TUNEL staining. Our results show significant increment in the number of ovarian follicles expressing the gap junction subunit Cx43 after in vivo rGH treatment. Therefore, we conclude that growth hormone can modulate in vivo gap junction assembly at early stages of folliculogenesis.

Expression of connexin 43 and gap junctional intercellular communication in the cumulus-oocyte complex in sheep

To evaluate the effects of FSH, LH and/or cAMP on expression of connexin 43 (Cx43) in the ovine cumulus-oocyte complex (COC) and gap junctional intercellular communication (GJIC) of cumulus cells, two experiments were carried out. In experiment 1, Cx43 was immunodetected in the COC, before or after maturation, obtained from non-treated or FSH-treated ewes. The expression of Cx43 in the COC was greater (P < 0.01) on day 16 than on day 15 of the estrous cycle. In vivo FSH treatment decreased (P < 0.02) Cx43 expression on day 16 but not on day 15 of the estrous cycle. In experiment 2, intact COCs or isolated cumulus cells obtained from small and large follicles from FSH-treated ewes were cultured with or without FSH, LH or cAMP agonist and evaluated for GJIC by laser cytometry. For large follicles, the basal rate of GJIC was greater (P < 0.01) for cumulus cells in intact COCs than for isolated cumulus cells. FSH increased (P < 0.04) GJIC in cumulus cells in intact COCs and tended to increase (P < 0.1) GJIC in isolated cumulus cells from small follicles but decreased (P < 0.01) GJIC in cumulus cells in intact COCs from large follicles. LH also increased (P < 0.01) GJIC in isolated cumulus cells from small follicles but decreased GJIC in intact COCs (P < 0.01) and isolated cumulus cells (P < 0.02) from large follicles. cAMP increased (P < 0.01) the GJIC in both intact COCs and cumulus cells from small and large follicles. These results indicate that day of estrous cycle, stage of maturation and duration of FSH treatment affect expression of Cx43 in ovine COCs. In intact COCs, GJIC in cumulus cells was enhanced, probably due to the presence of the oocyte. In addition, the effects of FSH and LH, but not cAMP, on GJIC of cumulus cells depended on the stage of follicular development and on the presence of the oocyte.

Cumulus expansion, nuclear maturation and connexin 43, cyclooxygenase-2 and FSH receptor mRNA expression in equine cumulus-oocyte complexes cultured in vitro in the presence of FSH and precursors for hyaluronic acid synthesis

The aim of this study was to investigate cumulus expansion, nuclear maturation and expression of connexin 43, cyclooxygenase-2 and FSH receptor transcripts in equine cumuli oophori during in vivo and in vitro maturation in the presence of equine FSH (eFSH) and precursors for hyaluronic acid synthesis. Equine cumulus-oocyte complexes (COC) were cultured in a control defined medium supplemented with eFSH (0 to 5 micrograms/ml), Fetal Calf Serum (FCS), precursors for hyaluronic acid synthesis or glutamine according to the experiments. After in vitro maturation, the cumulus expansion rate was increased with 1 microgram/ml eFSH, and was the highest with 20% FCS. It was not influenced by precursors for hyaluronic acid synthesis or glutamine. The expression of transcripts related to cumulus expansion was analyzed in equine cumulus cells before maturation, and after in vivo and in vitro maturation, by using reverse transcription-polymerase chain reaction (RT-PCR) with specific primers. Connexin 43, cyclooxygenase-2 (COX-2) and FSH receptor (FSHr) mRNA were detected in equine cumulus cells before and after maturation. Their level did not vary during in vivo or in vitro maturation and was influenced neither by FSH nor by precursors for hyaluronic acid synthesis. Results indicate that previously reported regulation of connexin 43 and COX-2 proteins during equine COC maturation may involve post-transcriptional mechanisms.

Protection of porcine oocytes against cell damage caused by oxidative stress during in vitro maturation: role of superoxide dismutase activity in porcine follicular fluid

To elucidate the beneficial effects of porcine follicular fluid (pFF) added to maturation medium on the sustenance of cytoplasmic maturation responsible for the subsequent developmental competence after in vitro fertilization (IVF) of porcine oocytes, we focused on the antioxidative role of pFF in its function of protecting oocytes from reactive oxygen species (ROS)-induced cell damage. Porcine follicular fluid collected from small (2-6 mm) follicles had about 7.2-fold higher levels of superoxide dismutase (SOD) activity than that of fetal bovine serum (FBS), and this activity was markedly blocked by the CuZn-SOD inhibitor, diethyldithiocarbamate (DETC). The interruption of meiotic progression and the increasing intracellular glutathione (GSH) content throughout the maturation period, as well as an outbreak of DNA damage in oocytes and cumulus cells were difficult to detect in oocytes cultured in a medium supplemented with 10% pFF, even in the presence of ROS generated by the hypoxanthine-xanthine oxidase system, whereas cell damage encompassed by ROS was prominent in oocytes cultured with 10% FBS and 10% pFF plus 100 microM DETC. Similarly, significant enhancement to the degree of transformation of the sperm nucleus into the male pronucleus (MPN) after in vitro fertilization was shown by the addition of pFF to the maturation medium. The presence of DETC during in vitro maturation reduced the ability of oocytes to promote MPN formation to the same extent as oocytes matured with FBS. The proportion developing to the blastocyst stage was increased in oocytes that matured with pFF, but this developmental competence was significantly lowered by treatment with DETC (P < 0.05). These findings suggest that pFF plays a critical role in protecting oocytes from oxidative stress through a higher level of radical scavenging activity elicited from SOD isoenzymes, resulting in the enhancement of cytoplasmic maturation responsible for developmental competence postfertilization.