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PubMed2002

Ionic currents activated via purinergic receptors in the cumulus cell-enclosed mouse oocyte.

Several chemical signals synthesized in the ovary, including neurotransmitters, have been proposed to serve as regulators of folliculogenesis, however, their mechanisms of action have not been completely elucidated. Here, electrophysiological and molecular biology techniques were used to study responses generated via purinergic stimulation in cultured mouse cumulus cell-enclosed oocytes (CEOs). Application of extracellular ATP elicited depolarizing responses in CEOs. Using the voltage clamp technique by impaling oocytes with two microelectrodes, we determined that these responses were mainly due to activation of two distinct ionic currents. The first corresponded to the opening of Ca2+-dependent Cl- channels (I(Cl(Ca))) and the second to the opening of Ca2+-independent channels that are permeable to Na+ (I(c+)). The potency order for different nucleotides (50 micro M) was UTP > ATP > 2meS-ATP > ADP, and alpha,betame-ATP and adenosine were found to be inactive. Suramin (100 micro M) blocked the response elicited by ATP or UTP. In addition, voltage dependent K+ currents activated by depolarization of CEOs were characterized. All CEO ionic currents recorded from the oocyte were completely inhibited by octanol (1 mM), a gap junction blocker. Thus, purinergic responses and K+ currents originate mainly in the membrane of cumulus cells. Transcripts of the purinergic receptor P2Y2 subtype were amplified by polymerase chain reaction from the cDNA of granulosa cells or cumulus cells. This study shows that P2Y2 receptors are expressed in CEOs, and that their stimulation opens at least two different types of ion channels. Both the ion channels and the receptors seemed to be located in the cumulus cells, which transmit their corresponding electrical signals to the oocyte via gap junction channels.

Adenosine Diphosphate↗
PubMed2001

Stereologic characterization of bovine (Bos taurus) cumulus-oocyte complexes aspirated from small antral follicles during the diestrous phase.

Bovine ovarian cumulus-oocyte complexes (COCs) are used for in vitro maturation and fertilization after selection by size and morphology, but their developmental potential remains low. Stereology could provide more objective criteria for selecting the most competent complexes, but its application is lacking in cattle. COCs from small (1-4 mm) antral follicles were aspirated from diestrous ovaries of Holstein-Friesian cows, fixed in glutaraldehyde, randomly embedded in glycol-methacrylate, and sectioned at 20 microm. The unbiased nucleator principle was used for estimating the mean volumes of complexes, oocytes, cumulus cells, and nuclei of oocytes and cumulus cells. The thickness of the zona pellucida and the relative numerical percentages of the several morphologic types of cumulus cells were also evaluated. The optical disector procedure was used for cumulus cell sampling. Volume estimation based on a real physical unique point did not differ from those based on a particular point among many or on a virtual central point, and the mean cumulus cell volume was estimated by using the single section bearing the unique reference point. Quantitative data showed that COCs appear heterogeneous for all studied parameters and that the cumulus mass contains three different cell populations.

Animals↗
PubMed2001

Involvement of connexin 43 in meiotic maturation of bovine oocytes.

In ovarian follicles, cumulus cells provide the oocyte with small molecules that permit growth and control maturation. These nutrients reach the germinal cell through gap junction channels, which are present between the cumulus cells and the oocyte, and between the cumulus cells. In this study the involvement of intercellular communication mediated by gap junction channels on oocyte maturation of in vitro cultured bovine cumulus-oocyte complexes (COCs) was investigated. The stages of oocyte maturation were determined by Hoechst 33342 staining, which showed that 90% of COCs placed in the maturation medium for 24 h progress to the metaphase II stage. Bovine COC gap junction communication was disrupted initially using n-alkanols, which inhibit any passage through gap junctions. In the presence of 1-heptanol (3 mmol l(-1)) or octanol (3.0 mmol l(-1) and 0.3 mmol l(-1)), only 29% of the COCs reached metaphase II. Removal of the uncoupling agent was associated with restoration of oocyte maturation, indicating that treatment with n-alkanols was neither cytotoxic nor irreversible. Concentrations of connexin 43 (Cx43), the major gap junction protein expressed in the COCs, were decreased specifically using a recombinant adenovirus expressing the antisense Cx43 cDNA (Ad-asCx43). The efficacy of adenoviral infection was > 95% in cumulus cells evaluated after infection with recombinant adenoviruses expressing the green fluorescence protein. RT-PCR performed on total RNA isolated from Ad-asCx43-infected COCs showed that the rat Cx43 cDNA was transcribed. Western blot analysis revealed a three-fold decrease in Cx43 expression in COCs expressing the antisense RNA for Cx43. Injection of cumulus cells with Lucifer yellow demonstrated further that the resulting lower amount of Cx43 in infected COCs is associated with a two-fold decrease in the extent of coupling between cumulus cells. In addition, oocyte maturation was decreased by 50% in the infected COC cultures. These results indicate that Cx43-mediated communication between cumulus cells plays a crucial role in maturation of bovine oocytes.

Adenoviridae↗
PubMed2002

Development of bovine oocytes reconstructed with different donor somatic cells with or without serum starvation.

We conducted this study to examine whether serum starvation in culture contributes to better development of bovine reconstructed oocytes and to evaluate which serum-starved somatic cell is the most effective for cloned calf production. In Experiment 1, donor cells of four different types (cumulus cells, ear fibroblasts, oviduct cells and uterine cells) were either serum-starved or not before fusion with enucleated oocytes, and reconstructed oocytes were further cultured for 168 h. Regardless of serum starvation, cumulus cells or ear fibroblasts yielded higher (P < 0.05) rates of fusion than other cells (62.6-69.3 versus 33.3-38.7%). In the serum-starved group, the first cleavage after reconstruction was significantly increased in cumulus cells and ear fibroblasts, compared with oviduct cells (93.4-94.3 versus 78.8-86.0%), and oocytes reconstructed with either of these yielded more blastocysts than oocytes reconstructed with oviduct or uterine cells (40.6-43.8 versus 20.3-19.0%). We observed a similar pattern in the non-starved group, but we found a significant increase in blastocyst formation was found only in cumulus cells compared with other donor cells (42.6 versus 15.4-27.7%). Overall comparison showed that serum starvation increased the rates of cleavage and development to the blastocyst stage, but we found a statistical significance only in the cleavage rate (80.0 versus 89.5%). In Experiment 2, we transferred randomly selected 59 blastocysts that were developed from oocytes reconstructed with serum-starved cells to 44 synchronised recipients. Of those recipients, 23 became pregnant on Day 60 after transfer (52.3%) and 12 (27.3%) delivered cloned calves. The mean gestation length and birth weight was 275 +/- 8 days and 39.6 +/- 15.6 kg, respectively. Although there was no significant difference among donor cells, blastocysts that were derived from oocytes reconstructed with ear fibroblasts yielded the highest rates of pregnancy (50.0%) and delivery (27.3%). In conclusion, serum starvation is effective for improving preimplantation development of oocytes reconstructed with cumulus or ear fibroblast cells and it may positively influence on obtaining better pregnancy outcome.

Animals↗
PubMed2006

Developmental ability of cloned embryos from neural stem cells.

The success rate is generally higher when cloning mice from embryonic stem (ES) cell nuclei than from somatic cell nuclei, suggesting that the embryonic nature or the undifferentiated state of the donor cell increases cloning efficiency. We assessed the developmental ability of cloned embryos derived from cultured neural stem cell (NSC) nuclei and compared the success rate with that of embryos cloned from other donor cells such as differentiated NSCs, cumulus cells, Sertoli cells and ES cells in the mouse. The transfer of two-cell cloned embryos derived from cultured NSC nuclei into surrogate mothers produced five live cloned mice. However, the success rate (0.5%) was higher in embryos cloned from cultured NSC nuclei than from differentiated NSCs (0%), but lower than that obtained by cloning mice from other cell nuclei (2.2-3.5%). Although the in vitro developmental potential to the two-cell stage of the cloned embryos derived from NSC nuclei (73%) was similar to that of the cloned embryos derived from other somatic cell nuclei (e.g., 85% in Sertoli cells and 75% in cumulus cells), the developmental rate to the morula-blastocyst stage was only 7%. This rate is remarkably lower than that produced from other somatic cells (e.g., 50% in Sertoli cells and 54% in cumulus cells). These results indicate that the undifferentiated state of neural cells does not enhance the cloning efficiency in mice and that the arrest point for in vitro development of cloned embryos depends on the donor cell type.

Animals↗
PubMed2005

Morphological and biochemical dynamics of porcine cumulus-oocyte complexes: role of cumulus expansion in oocyte maturation.

The process of cumulus expansion is a current topic of interest for in vitro production of embryos. In the present study, we examined the components of cumulus expansion, molecular mechanisms of cumulus expansion, and role of cumulus expansion for porcine oocyte maturation. The degree of cumulus expansion in the porcine cumulus-oocyte complexes (COCs) increased gradually until 48 h in culture in TCM-199. On the other hand, when the COCs were cultured in TCM-199 with a hyaluronan synthesis inhibitor and hyaluronidase, they showed no evidence of cumulus expansion during the culture period. Furthermore, the expression of hyaluronan synthase 2 (has2) in cumulus cells is accompanied by cumulus expansion. Hyaluronan receptor CD44 mRNA expressed in the cumulus cell, but not in the oocyte extracts. CD44 protein also expressed in/on the membrane of cumulus cells and its expression increased in a manner dependent on the degree of cumulus expansion. Moreover, we found that hyaluronan-CD44 system during cumulus expansion induces the activation of maturation promoting factor, resulting in germinal vesicle breakdown of the oocytes, and the tyrosine-phosphorylation of Cx43 in the COCs. The present results showed that the main component of cumulus expansion in the COCs is hyaluronan; the hyaluronan-CD44 system during cumulus expansion regulates the disruption of gap junctions in the COCs, and concurrently controls the incidence of meiotic resumption in the porcine oocytes.

Animals↗
PubMed1991

Heterologous cell contacts and metabolic coupling in bovine cumulus oocyte complexes.

The integrity of the cumulus cell processes were studied in four categories of bovine cumulus oocyte complexes (COCs) selected on their morphological characteristics. Three different types of cumulus cell process endings (CCPEs) were identified, one penetrating the cortex, another not penetrating the cortex, and a third form was intermediate and more rare in appearance. The process endings that penetrated the cortex frequently made gap junctions with the oolemma. The division of the three types of CCPEs over the four different COC categories was specific for three of the four categories. The first-category COC predominantly possessed the penetrating CCPE, the fourth-category COC possessed predominantly the nonpenetrating CCPE, and the second and third categories had both types of CCPEs. The metabolic coupling of the cumulus-oocyte contacts was assessed by means of incorporation of 3H-choline into the oocyte. The majority of category 4 COCs transferred low levels of choline into the oocyte while the majority of the oocytes of the other three categories transferred high levels of choline into the oocyte. Category 4 includes a smaller proportion of oocytes capable of cleaving after fertilization than the other three categories. This reduced developmental capacity is probably due to the loss of metabolic coupling before the onset of culture.

Animals↗
PubMed1997

Effects of epidermal growth factor and follicle-stimulating hormone during in vitro maturation on cytoplasmic maturation of porcine oocytes.

The present study was undertaken to investigate the influence of epidermal growth factor (EGF) and follicle-stimulating hormone (FSH) during in vitro maturation on cytoplasmic maturation of porcine oocytes as revealed by the success of fertilization and by the changes in the pattern of protein synthesis in oocytes and cumulus cells. For fertilization studies, oocyte-cumulus cell complexes (OCC) were cultured in media containing human recombinant EGF (1 ng/ml) or FSH (1.5 microg/ml) or both for 44 hr prior to fertilization with fresh sperm for 6-8 hr. The oocytes were then fixed, stained, and examined as whole mounts following an additional 14 hr of culture. Addition of EGF, FSH, and EGF + FSH significantly increased the proportion of oocytes reaching MII stage. The addition of EGF alone significantly decreased the percentage of polyspermic oocytes and increased the proportion of monospermic oocytes forming 2 normal pronuclei. FSH abolished these effects of EGF and significantly increased the percentage of polyspermic oocytes forming more than 2 pronuclei when added alone or with EGF. For protein analysis, OCC were cultured in media containing the above hormones for 6, 24, and 44 hr and exposed to 0.5 mCi/ml L-[35S]methionine during the last 3 hr of cultures. The oocytes and cumulus cells were separated prior to lysis in SDS sample buffer, and denatured polypeptides were separated by 1-dimensional SDS-PAGE. In the oocyte, addition of EGF and FSH alone stimulated the synthesis of 34, 45, and 97 kDa proteins after 6 hr of culture; however, the addition of EGF and FSH together was without any effect. After 24 hr, EGF alone inhibited the synthesis of these peptides, whereas FSH alone and with EGF maintained the stimulation of synthesis of 34 and 45 kDa proteins. Two additional peptides corresponding to 66 and 200 kDa appeared at this time as a result of exposure to FSH alone or with EGF. After 44 hr of culture, these 2 new peptides were observed in all groups and the stimulatory effect of FSH and FSH + EGF was still evident. An additional peptide of 26 kDa appeared at this time as a result of FSH and EGF + FSH treatments. In the cumulus cells, EGF and FSH each alone induced the synthesis of a new peptide of 26 kDa after 6 hr of culture. FSH when added alone or with EGF induced the synthesis of an additional peptide of 29 kDa, the synthesis of which remained unchanged at 24 and 44 hr. After 24 hr, FSH alone and in combination with EGF induced the synthesis of an additional 38 kDa peptide and its synthesis was still maintained at 44 hr. EGF alone had no effect on protein synthesis in cumulus cells at 24 and 44 hr. These studies indicate that EGF may have a physiological role in the regulation of cytoplasmic maturation of porcine oocytes.

Animals↗
PubMed1997

Support for the development of bovine embryos in vitro by secretions of bovine trophoblastic vesicles derived in vitro.

This study evaluated whether trophoblastic tissue derived in vitro secretes factors that support bovine embryonic development in vitro. The embryotrophic activity of these secretions was analysed in three different culture conditions based on TCM-199: (1) in a routine culture system using cumulus cells and 10% oestrous cow serum; (2) without cells but with 10% oestrous cow serum; and (3) under serum-free conditions. Rates of development to the 5-8-cell and blastocyst stages, as well as numbers of inner cell mass and trophectoderm cells of blastocysts were determined. In the absence of cumulus cells, cleavage rates of 5-8-cell embryos were significantly (P < 0.05) higher in trophoblastic vesicle-conditioned medium than in TCM-199 in both the presence (71% versus 49%) and absence (70% versus 49%) of serum. Trophoblastic vesicle-conditioned medium had a significant (P < 0.05) positive effect on the rate of development to the blastocyst stage when compared with TCM-199 in the presence of cumulus cells and serum (39% versus 33%), only serum (26% versus 19%), or in the absence of cells and serum (21% versus 5%). The numbers of inner cell mass and trophectoderm cells, and total number of cells in blastocysts produced in the cumulus cell coculture system in serum-free trophoblastic vesicle-conditioned medium or TCM-199 supplemented with serum were greater than those of blastocysts produced without cumulus cells or serum. Fractionation of serum-free trophoblastic vesicle-conditioned medium by ultrafiltration (10 kDa cut off) confined the embryotrophic activity mainly to the low molecular mass fraction. This study shows that serum-free trophoblastic vesicle-conditioned medium contains potent embryotrophic factors which act in a complementary manner to those secreted by cumulus cells and those supplemented with serum and result in reliably high blastocyst rates in the range of 40%. Since contamination of trophoblastic vesicle-conditioned medium with serum proteins can be avoided, this medium may be a reasonable source for the purification of specific embryotrophic factors.

Animals↗
PubMed2006

Differential response of cumulus cell-enclosed and denuded mouse oocytes in a meiotic induction model system.

In this study we have examined the effects of denuded oocyte coculture with dissociated cumulus cells (CC) or intact oocyte-CC complexes on meiotic resumption. When denuded oocytes (DO) or cumulus cell-enclosed oocytes (CEO) were cultured in 40-microl drops of medium under oil, and held in meiotic arrest with 4 mM hypoxanthine plus 25 microM dbcAMP, they underwent germinal vesicle breakdown (GVB) at similar frequencies (34%-35%). Coculture of DO with complexes or dissociated CCs stimulated maturation (50% and 61% GVB, respectively), with no effect of DO on maturation of cocultured CEO (32% GVB). This coculture effect was increased with the number of CCs added to the culture drop. When either glucose or glutamine was eliminated from the medium, no meiotic induction resulted from cocultured CCs. When CEO were cultured alone in microdrops, increasing their number from 10 to 50 significantly lowered the percentage resuming maturation, an effect also reduced by removing glucose and/or glutamine from the medium. This effect was not observed with DO. When inhibitory medium was conditioned overnight with complexes, subsequent culture with DO led to higher maturation percentages than culture in unconditioned medium; however, when CEO were cultured in conditioned medium, there was either no effect or increased inhibition of maturation. Assay of glucose and pyruvate in spent medium showed that DO cultured alone consumed glucose and pyruvate, but under CC coculture conditions more glucose was consumed and significant amounts of pyruvate accumulated in the medium, changes that led to an increase in the maturation of DO. Further experiments showed that DO were more sensitive than CEO to the meiosis-inducing effect of pyruvate. These results demonstrate different responsiveness of DO and CEO to coculture conditions and question the physiological relevance of denuded oocyte/CC coculture to study meiotic induction.

Animals↗
PubMed2004

Down-regulated expression of A disintegrin and metalloproteinase with thrombospondin-like repeats-1 by progesterone receptor antagonist is associated with impaired expansion of porcine cumulus-oocyte complexes.

ADAMTS-1, a member of the A disintegrin and metalloproteinase family of proteases, is expressed in rodent follicles via progesterone receptor (PR)-dependent pathways. However, the functional relationship between ADAMTS-1 expression and PR has not been studied extensively in other species. In the present study, we investigated the time-dependent changes in ADAMTS-1 expression in cumulus cells of porcine cumulus-oocyte complexes (COCs), and the roles of ADAMTS-1 in cumulus expansion during in vitro maturation of oocytes. ADAMTS-1 message was not detected in cumulus cells at the time of collection from the follicles. In response to gonadotropins, ADAMTS-1 mRNA was dramatically up-regulated and reached a maximum at 20 h. The level of mature ADAMTS-1 protein increased in a time-dependent manner with a maximum level at 40 h. The induction of ADAMTS-1 mRNA and protein was significantly decreased by the addition of PR antagonist RU486 to the cultures. However, RU486 did not affect the expression of ADAMTS-4 or factors that had been reported to be required for COC expansion (TSG-6, versican, HA synthase-2). COCs cultured with FSH and LH for 40 h exhibited prominent cumulus expansion. The expansion was reduced significantly by the addition of either RU486 or Galardin, a broad-spectrum matrix metalloproteinase inhibitor. These results suggest that the expression and induction of ADAMTS-1 through receptor-mediated action of progesterone in cumulus cells is one of the essential requirements for gonadotropin-regulated cumulus expansion of porcine COCs.

Animals↗
PubMed1988

Cytochemical localization of adenylate cyclase in bovine cumulus-oocyte complexes.

The ultrastructural localization of adenylate cyclase was studied in bovine cumulus-oocyte complexes. Adenylate cyclase was observed on the plasma membrane of the oocyte and occasionally on the plasma membrane of cumulus cells. The cytochemical observations presented demonstrate that there is more adenylate cyclase in cumulus-oocyte complexes after in vitro stimulation with forskolin. The presence of adenylate cyclase upon the oocyte was more pronounced. In addition adenylate cyclase appeared to be localized on the cumulus cells, especially between junctional complexes of cumulus cells and on cumulus cell processes contacting the oocyte. The cumulus cells never showed the presence of adenylate cyclase in the absence of forskolin. No changes in the presence of adenylate cyclase were observed during in vitro meiotic maturation.

Adenylyl Cyclases↗
PubMed2005

Mouse oocytes regulate metabolic cooperativity between granulosa cells and oocytes: amino acid transport.

A search for genes expressed more highly in mouse cumulus cells than mural granulosa cells by subtraction hybridization yielded Slc38a3. SLC38A3 is a sodium-coupled neutral amino acid transporter having substrate preference for l-glutamate, l-histidine, and l-alanine. Detectable levels of Slc38a3 mRNA were found by in situ hybridization in granulosa cells of large preantral follicles, but levels were higher in all granulosa cells of small antral follicles; expression became limited to cumulus cells of large antral follicles. Expression of Slc38a3 mRNA in granulosa cells was promoted by fully grown oocytes from antral follicles but not by growing oocytes from preantral follicles. Fully grown oocytes were dependent on cumulus cells for uptake of l-alanine and l-histidine but not l-leucine. Fully grown but not growing oocytes secreted one or more paracrine factors that promoted cumulus cell uptake of all three amino acids but of l-alanine and l-histidine to a much greater extent than l-leucine. Uptake of l-leucine appeared dependent primarily on contact-mediated signals from fully grown oocytes. Fully grown oocytes also promoted elevated levels of Slc38a3 mRNA and l-alanine transport by preantral granulosa cells, but growing oocytes did not. Therefore, fully grown oocytes secrete one or more paracrine factors that promote cumulus cell uptake of amino acids that oocytes themselves transport poorly. These amino acids are likely transferred to oocytes via gap junctions. Thus, oocytes use paracrine signals to promote their own development via metabolic cooperativity with cumulus cells. The ability of oocytes to mediate this cooperativity is developmentally regulated and acquired only in later stages of oocyte development.

Alanine↗
PubMed2002

Roles of gene transcription and PKA subtype activation in maturation of murine oocytes.

The aims of this study were to examine the role of transcription and the coincident involvement of type I and type II protein kinase A (PKA) in the resumption of meiosis in murine cumulus-oocyte complexes (COCs) using the transcriptional inhibitors 5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole (DRB) and alpha-amanitin. The first series of experiments was designed to: (i) characterize the role of transcription in gonadotrophin-mediated and spontaneous maturation of murine oocytes; (ii) examine the roles of specific gonadotrophins (FSH versus hCG) and cumulus cells in transcriptionally mediated oocyte maturation; and (iii) determine the reversibility of the transcriptional arrest of meiosis. In the presence of FSH, transcriptional inhibitors arrested germinal vesicle breakdown (GVBD) (DRB: 2 +/- 2% and control: 76 +/- 2%; alpha-amanitin: 4 +/- 4% and control: 70 +/- 4%). Furthermore, cumulus cells were required for transcriptional inhibitors to arrest GVBD (DRB with cumulus cells: 0 +/- 15%; DRB without cumulus cells: 94 +/- 13%; alpha-amanitin with cumulus cells: 15 +/- 2%; alpha-amanitin without cumulus cells: 99 +/- 2%). Thus, in mice, FSH-mediated GVBD uses a transcriptional mechanism, which probably occurs within the cumulus cell compartment. In a second series of experiments, the role of transcription in mediating the resumption of meiosis after activation of either type I or type II PKA was examined. Activation of type I PKA in murine COCs resulted in an arrest of GVBD that was independent of a transcriptional event (with DRB: 7 +/- 9% GVBD; without DRB: 11 +/- 9% GVBD). In contrast, activation of type II PKA resulted in a resumption of meiosis, which required the occurrence of gene transcription (with DRB: 12 +/- 9% GVBD; without DRB: 80 +/- 9% GVBD). As FSH binding to cumulus cells activates the PKA second messenger system, our results indicate that, in cultured murine COCs, FSH binding to cumulus cells results in the activation of type II PKA, which, in turn, mediates a downstream transcriptional event required for the initiation of GVBD.

Amanitins↗
PubMed1995

A novel biological aspect of ovarian oxytocin: gene expression of oxytocin and oxytocin receptor in cumulus/luteal cells and the effect of oxytocin on embryogenesis in fertilized oocytes.

Recently, several authors have reported the existence of oxytocin (OT) in mammalian granulosa-luteal cells after ovulation. The purpose of this study was to examine the evidence for gene expression and localization of OT and OT receptor (OTR) in the cumulus cells surrounding the oocytes. Cumulus cells with mature oocytes were obtained from experimental and clinical in vitro fertilization-embryo transfer (IVF-ET) programs. OT and OTR gene expression was analyzed with reverse transcriptase-polymerase chain reaction (RT-PCR) and RT-PCR/single strand conformation polymorphism (SSCP). OT gene expression was detected in mouse and human cumulus cells. The results of RT-PCR/SSCP showed that the structure of OT mRNA in cumulus cells was similar to that in the hypothalamus. Furthermore, OTR gene expression was clearly demonstrated in human cumulus cells, and a weak positive signal was observed in human oocytes. Immunocytochemical staining of OTR was clearly detected in human cumulus cells. The rate of mouse blastocyst development was significantly higher in the group cultured with OT than that without OT. These results are the first observations of simultaneous OT and OTR gene expression in cumulus cells, suggesting that ovarian OT might have some physiological role in the early stage of embryo development.

Animals↗
PubMed1980

Binding of human chorionic gonadotropin by rat cumuli oophori and granulosa cells: a comparative study.

Cumulus oocyte complexes isolated from PMS gonadotropin-primed immature rats bind [125I]hCG. Unlabeled hCG and ovine LH compete with the labeled hormone for binding sites, while rat FSH and ovine PRL are without effect. Since specific binding of [125I]hCG could not be detected in preparations of oocytes from which the cumuli had been removed, it appears that the binding exhibited by the complex can be attributed to the cumulus cells. The concentration dependence of binding is consistent with the presence of one population of high affinity (apparent Kd, 1.4 X 10(-10) M) binding sites (223 +/- 33 sites/cumulus cell). Rat granulosa cells bind hCG with equivalent apparent affinity and specificity but contain more sites (2060 +/- 180/cell) than cumulus cells.

Animals↗
PubMed2003

Morphology of canine cumulus-oocyte complexes in pre-pubertal bitches.

The morphology of canine cumulus-oocyte complexes (COCs) before puberty is still unknown. Therefore, the aim of our study was to elucidate the morphological characteristics of pre-pubertal oocytes and cumulus cells by light microscopy, scanning electron microscopy and transmission electron microscopy. The pre-pubertal oocyte was characterized by accumulation of lipid yolk droplets in the cytoplasm as well as high energy metabolism, low protein synthesis and high transcriptional activity of the cumulus cells. The cumulus cells, which revealed a prominent nucleus and few cytoplasm, communicated with each other by few short processes and exhibited merely a small amount of processes reaching the oocyte. Our studies imply that both the oocyte and the cumulus cells of canine COCs before puberty reveal characteristic morphological features which are correlated with changes in oocyte metabolism and cumulus cell communication.

Animals↗
PubMed1991

Maturation of the rat cumulus-oocyte complex: structure and function.

The cumulus cells that surround the mammalian oocyte become dispersed following the preovulatory surge of the pituitary gonadotropin, luteinizing hormone (LH). We have examined cumulus-oocyte complexes of PMSG-primed immature rats before and at 1, 2, 3, 4, 6, and 8 hr after injection of human chorionic gonadotropin (hCG), which acts on the rat ovary like the pituitary gonadotropin. Associations between projections of the cumulus cells and the oocyte were analyzed in thin sections. We observed that some cumulus projections were greatly enlarged where they associate with the oocyte. These enlarged regions were filled with numerous small vesicles. Gap junctions between cumulus cell projections and the oocytes were small. We quantitated the number and size of gap junctions between cumulus cells. The number of small gap junctions (less than 1 microM) between cumulus cells did not change significantly over the 8-hr period after hCG administration. Larger gap junctions, however, showed a general downward trend beginning after the third hour post hCG. Light microscopic observations of plastic sections revealed that dispersion of the cumulus oophorus is not observed until after 4 hr post-hCG, but between 4 and 8 hr after gonadotropin administration the cumulus becomes markedly dispersed. In the majority of the oocytes in these complexes the germinal vesicle (GV) displayed some irregularity in shape at 2 hr post-hCG, although absence of the GV was not observed until later. Our observations suggest a new means of communication in the cumulus-oocyte complex by the vesicle-filled enlargements of the cumulus cell projections at the oocyte surface. They further indicate that the decrease in metabolic coupling observed in rat cumulus-oocyte complexes soon after exposure to LH is not associated with a change in number and size of the gap junctions between the cumulus cells. We suggest that it is either the disruption of the gap junctions at the region of contact of the cumulus cell projections with the oocyte surface or the operation of a gating mechanism that blocks the junctional channels without affecting their morphological appearance that is responsible for uncoupling of the oocyte from the cumulus cells.

Animals↗