Developmental stage of the oocyte during antral follicle growth and cumulus investment determines in vitro embryo development of sow oocytes

The aim of the study was to determine the contribution of cumulus cells on the developmental competence of porcine oocytes during follicle growth. Oocytes from large (5-8mm) and small (2-3mm) follicles were cultured with or without follicle stimulating hormone (FSH), subsequently examined for nuclear stage and spindle morphology, or fertilized and cultured for embryo development, or analyzed for glutathione content. Additionally, the significance of cumulus investment, corona radiata cells, cumulus cell number and origin of cumulus cells for oocyte maturation were investigated. Small follicle oocytes cultured without FSH exhibited the highest incidence of spindle aberrations. Oocytes cultured without FSH exhibited reduced sperm penetration and blastocyst rates, and a higher proportion monospermic oocytes developed to the blastocyst stage when derived from large follicles. The glutathione content in oocytes increased during follicle growth and oocyte maturation, but no direct correlation between oocyte glutathione content and oocyte developmental capacity was observed. Oocytes with a bigger cumulus investment exhibited better embryo development. Oocytes with a single corona radiata cell layer (CROs) exhibited similar progression through meiosis to oocytes with more cumulus cell layers, but showed reduced embryo development. More blastocysts were observed when CROs were cultured with disconnected cumulus cells during IVM, but no blastocyst increase was observed when CROs were cocultured with a higher number of cumulus cells or with cumulus cells from large follicles. We conclude that increased developmental capacity of oocytes during follicle growth is intrinsic and whether cumulus cells originate from large or small follicles, their contribution to oocyte maturation remains unchanged. Further, cumulus investment can be used as a variable to predict oocyte developmental capacity.     

Gonadotropin stimulation regimens for follicular aspiration and in vitro embryo production from calf oocytes

Crossbred beef x dairy calves were randomly allocated at 3 wk of age to different gonadotropin treatment regimens for stimulation of follicle development and induction of oocyte maturation in vivo. Follicular responses were assessed laparoscopically, and oocytes were aspirated for assessment of maturational state or for in vitro fertilization (IVF) and culture to determine developmental capacity. Follicle-stimulating Hormone (FSH), administered in a single subcutaneous injection together with a low dosage of PMSG, was as effective as the same total dosage of FSH administered in 6 injections over a 3-d period. Without accompanying PMSG, this dose of FSH was ineffective in stimulating follicle development. The mean number of preovulatory follicles (> 5mm, with hyperemic appearance) doubled with each successive stimulation at 3-wk intervals, reaching 35 follicles per calf at 9 wk of age. Oocyte yields ranged from 55 to 81% of follicles aspirated, and did not differ significantly among age, FSH regimen and oocyte maturation stimulus. A combination of LH + FSH was more effective in stimulating cumulus cell expansion than LH by itself (73 vs 22% of recovered oocyte-cumulus cell complex (OCC) respectively; P<0.05). Of 33 unselected immature oocytes (cumulus unexpanded) subjected to in vitro maturation (IVM) and IVF, 30% developed to blastocysts during co-culture with bovine oviduct epithelial cells, which was not significantly different from 25% of 36 oocytes from adult ovaries which reached the blastocyst stage under similar conditions. The results indicate that follicle responses of calf ovaries to FSH stimulation increase progressively from 3 to 9 wk of age, and that oocytes recovered laparoscopically from these follicles produce blastocysts in culture at rates similar to oocytes from adult cattle ovaries collected at slaughter. The approach offers promise for embryo production from donor calves of superior genetic merit for embryo transfer, thereby enhancing the rate of genetic gain above that attainable by conventional breeding or by embryo transfer in adult cattle.     

Different intervals of ovum pick-up affect the competence of oocytes to support the preimplantation development of cloned bovine embryos

The objective of this study was to determine the effect of different frequencies of transvaginal ovum pick-up (OPU) on the quantity of recovered cumulus oocyte complexes (COCs) and subsequently the competence of matured oocytes to support the preimplantation development of cloned bovine embryos. The COCs were aspirated from the ovaries of 6 Chinese Holstein cows by transvaginal follicle aspiration twice a week (every 3 or 4 days) (Group I), every 5 days (Group II), once a week (every 7 days) (Group III), every 10 days (Group IV), and once every 2 weeks (every 14 days) (Group V). The developmental stages of the follicles were confirmed by the diameter of the dominant follicle (DF) and harvested COCs, and the dynamics of the follicular wave were clarified. In addition, extrusions of the first polar body (PB I) from the oocytes were observed at different time intervals after the initiation of in vitro maturation (IVM) to identify the appropriate culture time window for somatic cell nuclear transfer. Matured oocytes were used to produce cloned bovine embryos that were subsequently cultured in the goat oviduct. After 7 days, the embryos were flushed out, and the developmental rates of the blastocysts were compared among the five groups. The results showed that the aspirations of all follicles >or=3 mm in diameter (D1) induced and synchronized the dynamics of the follicular wave, and the subordinate follicles became atretic after 4 days (D5). Another follicular wave started between D7 and D10, and atresia in the subordinate follicles in the second follicular wave began on D14. The timing of meiotic progression (from the initiation of IVM to the extrusion of PB I) in the oocytes obtained by OPU was later than that of the oocytes obtained from the abattoir. Between 20 and 24 hr after the initiation of IVM, 20% of the oocytes extruded their PB I. Further, 80% (520/650) of the harvested COCs were arrested at metaphase II (MII) by 22 hr of the initiation of IVM and were used as cytoplast donors. The rates of development of the reconstituted embryos to the blastocyst stage were 23.1% (Group I), 15.0% (Group II), 10.9% (Group III), 4.9% (Group IV), and 29.0% (Group V). The results indicate that the developmental potential of follicles from the same living donors were different when different intervals of OPU were adopted and early atretic follicles from the second follicular wave had higher competence to support the early development of cloned bovine embryos.     

Developmental competence of bovine oocytes is not related to apoptosis incidence in oocytes, cumulus cells and blastocysts

The number of follicles undergoing atresia in an ovary is very high, and isolation of cumulus-oocyte complexes (COCs) from such atretic follicles may impair subsequent embryo development in vitro. Our aim was to study if stringent selection by morphological assessment of COCs can improve embryo development, and to evaluate whether oocyte diameter is related with apoptotic ratio in oocytes and blastocysts. COCs from slaughtered cattle were recovered by follicle aspiration and classified depending on oocyte diameter: (A) <110 microm; (B) 110-120 microm; (C) >120 microm. COCs were matured, fertilized and cultured in vitro. Early and late stages of apoptosis were detected by Annexin-V and TUNEL staining, respectively, in denuded oocytes, COCs and blastocysts. Immature oocytes from Group A showed higher apoptotic ratio assessed by TUNEL assay, and the COCs corresponding to this group also showed a higher proportion of apoptotic cumulus cells. After maturation, no differences were present in the incidence of apoptosis among oocytes from different groups, but COCs corresponding to the largest diameter showed less apoptotic cumulus cells. In addition, the percentage of apoptotic oocytes decreased during in vitro maturation in all groups. Apoptotic cell ratio (ACR) in blastocysts was not related to oocyte diameter. In conclusion, oocyte selection and oocyte morphological evaluation prior to maturation was not sufficient to select non-atretic oocytes. When oocyte diameter was used as an additional selection the embryonic developmental potential increased together with oocyte diameter, but this improvement was not related to a lower incidence of apoptosis in the largest oocytes.     

Effect of follicular size on in vitro developmental competence of oocytes and viability of embryos after transfer in the dromedary (Camelus dromedarius)

The aim of this work was to determine the effect of follicle size on camel oocyte quality as measured by developmental competence in vitro and in vivo. Ovaries from a local slaughterhouse were dissected to obtain two classes of follicle size: small (3-6 mm) and large (>6 mm) follicles. Quality of the oocytes was assessed after in vitro maturation (IVM), in vitro fertilization (IVF) and in vitro culture (IVC) of cumulus oocyte complexes (COCs). All cultures were done in four replicates at 38.5 degrees C, under 5% CO(2) and high humidity (>95%). Only COCs with cumulus and homogenous (dark) cytoplasm were used. The COCs were matured for 28 h in TCM-199 medium supplemented with 10% heat-treated fetal calf serum (FCS), 10 ng/mL EGF, and 250 microM cysteamine. Nuclear maturation rate for each class of follicle size was determined by contrast phase microscopy in a sample of COCs (n=30) denuded, fixed and stained with aceto-orcein. In vitro fertilization was performed using fresh semen (0.5 x 10(6)spermatozoa/mL in modified TALP-solution). Fertilized oocytes were cultured in mKSOMaa, under 5% O(2) and 90% N(2). The percentage of COCs reaching metaphase II (MII) after 28 h of maturation was 87% (26/30) and 73% (22/30) for oocytes originating from large and small follicles, respectively (P>0.1). The rate of total cleavage (two cells to blastocyst stage) was greater (P<0.05) for oocytes originating from large follicles (72%; 116/162) than for those derived from small follicles (59%; 140/237). The percentage of fertilized oocytes reaching the blastocyst stage was 35% (57/162) and 20% (48/237) for oocytes collected from large and small follicles, respectively (P<0.05). The viability of in vitro-produced hatched blastocyst from the two groups (15 from 3 to 6mm follicle size and 22 from follicles >6 mm) was assessed by transfer to synchronized recipients. None of the hatched blastocysts from small follicles resulted in a pregnancy whereas 68% (15/22) of the transferred hatched embryos from large follicles developed into a 25-day pregnancy. Of the resulting 15 pregnancies, 53% (n=8) aborted (five between 2 and 4 months and three between 5 and 7 months of pregnancy). The remaining seven pregnant females gave birth to normal healthy offsprings (four females and three males). The present study shows that dromedary oocytes developmental competence is acquired late during the final phase of follicular development and this developmental ability translates into greater pregnancy rates after transfer of in vitro produced hatched blastocysts.     

Relationship between bovine oocyte morphology and in vitro developmental potential

We investigated the relationship between the morphology of oocytes collected from small antral follicles and their developmental capacity. Immature oocytes were classified into seven groups and cultured in vitro for maturation (IVM), fertilization (IVF) and development to blastocysts (IVC). After IVF, sperm penetration and normal fertilization rates were higher in the oocytes whose cytoplasm appeared brown. The rate of polyspermy was highest in the oocytes whose cytoplasm was black. After IVC, the rates of cleavage and of development to the blastocyst stage were also higher in the brown oocytes. Although the oocytes with dark clusters in a pale cytoplasm showed lower cleavage rates, cleaved zygotes had high developmental rates the same as the oocytes with a brown cytoplasm. Transmission electron microscopy showed that the oocytes with a pale or black cytoplasm had organelles arranged differently from other oocytes before IVM. Most of the oocytes with a brown and homogeneous cytoplasm or small diameter had the characteristics of immature cytoplasm (large clusters of cortical granules) even after IVM. On the other hand, the brown oocytes with a dark zone at the periphery or with dark clusters showed the same arrangement of organelles as in vivo matured oocytes. The oocytes with a pale or black cytoplasm appeared to be degenerating and/or ageing. In conclusion, a dark ooplasm indicates an accumulation of lipids and good developmental potential, while a light-coloured ooplasm indicates a low density of organelles and poor developmental potential. A black ooplasm indicates ageing and low developmental potential.     

Plasminogen activator activity in cortical granules of bovine oocytes during in vitro maturation

In this study, we provide evidence that plasminogen activator of tissue-type (t-PA), at least, is present in extracts of bovine oocyte cortical granules, and that its activity varies significantly with the duration of oocyte in vitro maturation. Cortical granules were collected from bovine oocytes by means of micromanipulation, after 0, 12, or 24 h of IVM. Our results show that plasminogen activator activity of cortical granule extracts was significantly higher after 24 h of IVM than after 12 h of IVM or before IVM. This activity was apparently due, at least partly, to tissue-type plasminogen activator as shown immunologically. No evidence was found for the presence of urokinase-type plasminogen activator, plasminogen activator inhibitors or plasmin inhibitors in bovine oocyte cortical granule extracts. Our findings further support the hypothesis that t-PA activity of oocyte origin may have a role in oocyte maturation or fertilization, as well as in post-fertilization events, such as cortical reaction and formation of the zona block to polyspermy.     

Cytoplasmic changes in relation to nuclear maturation and early embryo developmental potential of porcine oocytes: effects of gonadotropins, cumulus cells, follicular size, and protein synthesis inhibition

Morphological and biochemical changes indicative of cytoplasmic maturation in relation to nuclear maturation progression and early embryo developmental potential was studied. Fluorescently labeled microfilaments and cortical granules were visualized by using laser scanning confocal microscopy. The mitogen-activated protein (MAP) kinase phosphorylation and cyclin B1 levels were revealed by Western blot. With the maturation of oocytes, cortical granules and microfilaments were localized at the cell cortex. A cortical granule-free domain (CGFD) and an actin-thickening area were observed over both the MII spindle of a mature oocyte and chromosomes of a nocodazole-treated oocyte, suggesting that chromosomes, but not the spindle, determined the localization of CGFD and actin-thickening area. In oocytes that are incompetent to resume meiosis, as indicated by the failure of germinal vesicle breakdown (GVBD), peripheral localization of cortical granules and microfilaments, phosphorylation of MAP kinase and synthesis of cyclin B1 did not occur after 44 hr in vitro. These cytoplasmic changes were also blocked when GVBD of meiotically competent oocytes was inhibited by cycloheximide. Culture of oocytes in a chemically defined medium showed that biological factors such as gonadotropins, cumulus cells and follicle size affected both nuclear and cytoplasmic maturation as well as embryo developmental potential. Absence of gonadotropins or removal of cumulus cells alone did not significantly influence GVBD or cyclin B1 levels, but decreased the final maturation and developmental ability of oocytes. A combination of gonadotropin absence and cumulus removal decreased GVBD, MAP kinase phosphorylation and embryo development. A high proportion of oocytes derived from small follicles were able to resume meiosis, synthesize cyclin B(1), phosphorylate MAP kinase and translocate CGs, but their maturation and embryo developmental ability were limited. Removal of cumulus cells from small follicle-derived oocytes severely affected their ability to undergo cytoplasmic and nuclear maturation.     

Effects of follicular atresia and size on the developmental competence of bovine oocytes: a study using the well-in-drop culture system

The effect of granulosa cell (GC) apoptosis and follicle size on the competence of bovine oocytes were studied using a well-in-drop (WID) oocyte/embryo culture system, which allows identification of follicular origin. Hatching rates of blastocysts did not differ (P>0.05) between oocytes cultured in the WID system (13%) and those cultured in the conventional group system (16%). Hatching rates of blastocysts were higher (P<0.05) in early atretic (17%) than in non-atretic (8%) and late atretic follicles (10%) of the same size (4-8mm), and in 6-8mm (22%) than in 4-5mm follicles (15%) at the early atretic stage. More oocytes (P<0.05) from late atretic (17%) than from non-atreteic (7%) or early atretic follicles (9%) of the same size (4-8mm) were arrested at Grade 1 cumulus expansion (only cells in the peripheral two layers began to expand). Similarly, more oocytes from 2 to 3mm follicles (30%) than from 6 to 8mm follicles (21%) at the same (late) atretic stage had Grade 1 cumulus expansion (P<0.05). Hatching blastocyst percentages of oocytes with Grade 3 (all layers of the cumulus except corona radiate cells expanded) or Grade 4 (full) cumulus expansion were higher in early atretic (20%) than in non-atretic (13%) or late atretic follicles (12%). Hatching blastocyst percentages of oocytes from follicles at the early atretic stage increased as cumulus expanded from Grade 2 (9%) to Grade 4 (27%). Regardless of the degree of follicle atresia, 72-76% of the floating cells in the follicular fluid (FF) were undergoing apoptosis. The floating cell density in FF was highly (r=0.6-0.7) correlated with oocyte developmental potency. In conclusion, the WID culture system was as efficient as group culture and allowed identification of follicular origin. Furthermore, the developmental potential of oocytes was affected by GC apoptosis, follicle size and cumulus expansion, and the floating cell density in FF could be used as a simple and non-invasive marker of oocyte quality.     

The effects of duration of in vitro maturation of bovine oocytes on subsequent development, quality and transfer of embryos

We examined the effects of IVM duration on rates of Korean Native Cow (KNC) first polar body extrusion, embryo development and offspring. Cumulus oocytes complexes were cultured in vitro for up to 24h. Extrusion of the first polar body was highest at 16h. At selected times during IVM, oocytes were fertilized and in vitro development was compared to blastocysts collected from superovulated KNC. After fertilization, the cleavage rate did not differ for oocytes with different durations of IVM, but the development rates of the 8-cell and blastocyst stages were significantly higher in IVM 18-h than other durations. The mean inner cell mass, trophectoderm and total cell numbers of in vivo blastocysts (40.0+/-3.8, 87.5+/-3.5 and 127.5+/-1.6, respectively) were similar to those for IVM 18-h group. When in vitro- and in vivo-derived blastocysts were transferred to Holstein heifer recipients, pregnancy and abortion rates did not differ among treatments. Mean gestation length was significantly shorter for in vivo-derived blastocysts than those derived from oocytes with 24h of IVM. Birth weight produced by the IVM 24-h group (32.0+/-2.2kg) was significantly higher than that of in vivo and IVM 18-h groups. The sex ratio of calves was similar between the in vivo and the IVM 24-h group, but all calves derived from the IVM 18-h group were males. Therefore, duration of bovine oocyte IVM played a critical role in embryo development and blastocyst cell number. In addition, it also affected birth weight and sex ratio.     

Storage of bovine isolated follicles: a new alternative way to improve the recovery rate of viable embryos from ovarian follicles of slaughtered cows

The vitality of bovine oocytes stored in isolated follicles was examined. The aim of this work was to prolong the time of in vitro manipulation of oocytes before their maturation and develop a new alternative of oocyte "capacitation" to improve the quality of in vitro produced embryos. Follicles were dissected from the ovaries of slaughtered cows; subsequently, follicles were divided according to their diameter into three categories (2-3, 3-4 and 4-6 mm), and stored at 17-18 degrees C for 24 or 48 h in a modified tissue culture medium-199 (TCM-199) with reduced pH. After that time, the cumulus-oocyte complexes (COCs) were isolated, matured, fertilized, and embryos cultured in vitro for a total of 9 days. The percentage of total blastocysts, and hatched blastocysts developed from oocytes, initially kept ("capacitated") for 24h at 17-18 degrees C, within follicles of 3-6mm size categories, were significantly higher than that oocytes of the control [of control oocytes] (44.9 and 30.3% versus 36.2 and 20.4%, respectively). The oocytes of follicles stored for 48 h at 17-18 degrees C already had decreased developmental capacity. Interesting data were obtained when COCs of the 3-4 and 4-6 categories were additionally divided into two subgroups according to their presumed developmental history (originating from the supposed growing "fit" in contrast to the supposed regressing "unfit" follicles). The higher improvement in the rate of hatched blastocysts from 24h stored oocytes was observed only in the subgroup originated from "fit" COCs (15.3 versus 25.0%, and 20.0 versus 34.4%, in the 3-4 and 4-6mm categories, respectively). The transfer of 26 blastocysts (developed of follicles kept for 24h at 17-18 degrees C) to 26 recipient heifers resulted in 18 pregnancies. Storage of follicles at 17-18 degrees C in vitro resulted not only in recovery of higher numbers of blastocysts of better quality but also facilitated the safe transport of follicles for a long distance. The extended, time of follicle storage before the proper oocyte maturation allowed also the synchronization of an appropriate number of recipient animals according to the number of isolated follicles.     

The endocannabinoid system modulates the ovarian physiology and its activation can improve in vitro oocyte maturation

The cannabinoid (CB) system has been involved in many aspects of reproduction and it is known that the systemic chronic use of exogenous CBs are deleterious to reproductive processes. Even so, it is not known what happens in relation to the physiology of the ovary when CB receptors are absent. The present study investigated the effect of the lack of CB1 and CB2 receptors in mice ovarian morphology, folliculogenesis, oocyte retrieval, and oocyte maturation and evaluated the use of Δ9-tetrahydrocannabinol (THC) on oocyte in vitro maturation (IVM) by comparing classical IVM and two-step IVM by analyzing the meiotic competence of the oocytes and their evolution toward embryos. Thus, when CB1 and CB2 receptors were missed, the ovary area and volume was significantly less and the action of the equine chorionic gonadotropin (eCG) hormone was diminished. In addition, the mutant genotypes had fewer ovarian follicles and they were less competent after eCG administration compared with wild-type mice, and this lack of CB receptors showed a mismatch of oocyte maturation. However, the in vitro use of THC showed improvements in oocytes IVM after a Pre-IVM step for 48 hr, as those oocytes reached a significantly higher polar body rate, a larger diameter and the best result on blastocysts rate was achieved when THC was used during the IVM step.     

Bovine oocyte diameter in relation to developmental competence

This study was conducted to determine the diameter of bovine oocytes that were able to attain their full developmental competence to blastocysts. Oocytes were recovered by aspiration of surface-visible follicles (1 to 7 mm in diameter) from slaughterhouse ovaries. Only healthy-looking cumulus-oocyte complexes were used for in vitro maturation, and they were divided into six groups based on diameter: < 110 microm, 110 to < 115 microm, 115 to < 120 microm, 120 to < 125 microm, 125 to < 130 microm and >/= 130 microm. Oocytes were processed through standard procedures for in vitro maturation, fertilization and culture. Following in vitro maturation or fertilization, some oocytes were stained to assess nuclear maturation and penetration rates. The numbers of embryos that cleaved at 42 h post insemination and developed to blastocysts and hatched blastocysts after 8 days of culture were recorded. The mean oocyte diameters were 114.0 +/- 4.8 microm. The oocytes displayed size-related ability to undergo meiotic maturation. The rates of nuclear maturation of oocytes in the greater than 115-microm size range were significantly higher than those of oocytes with diameters < 115 microm. In the < 120 microm diameter groups, the polyspermic fertilization rates of oocytes < 115 microm were significantly higher than those of oocytes 115 to < 120 microm in diameter. The rates of cleavage and development to blastocysts and hatched blastocysts rose as oocyte diameter increased. Among oocytes with a diameter >110 microm, oocytes < 120 microm were found to have significantly lower developmental competence than oocytes 120 to < 130 microm in diameter. These results suggest that bovine oocytes have acquired full meiotic competence at a diameter of 115 microm but not yet attained full developmental competence to blastocysts, and that oocytes have acquired full developmental competence at a diameter of 120 microm.     

In vitro development of individually matured bovine oocytes in relation to follicular wall atresia

Morphologically good-quality cumulus oocyte complexes (COCs) can originate from slightly atretic follicles. Biochemical and ultrastructural investigations reveal that a very high percentage of bovine antral follicles express some degree of atresia. The aim of the present study was to determine the developmental competence of good quality COCs in relation to their biochemically estimated follicular wall apoptosis. For experimental design a single oocyte maturation system was established, followed by group culture processing oocytes together according to their level of follicular wall atresia estimated by an ELISA for apoptotic cell death. Single oocyte culture during maturation reduced the developmental capacity of oocytes significantly (P < 0.01), with 5% blastocysts versus 25% after common group culture. Blastocyst formation for single oocyte maturation was found exclusively in oocytes isolated from luteal stage ovaries with low degree of apoptosis. The level of follicular wall apoptosis in luteal stage follicles (0.79 +/- 0.05 units/mg protein, n = 198) was lower than in follicular stage follicles (1.14 +/- 0.05 units/mg protein, n = 208). This was caused by significant higher levels in small (< 3.5 mm diameter) and large (> 5.5 mm diameter) follicles of the latter group. In conclusion, despite reduced developmental capacity after single oocyte maturation, we were able to reveal some functional relationship between oocyte origin and quality. It was shown that morphologically good quality COCs isolated from follicles with higher degree of apoptosis lose their developmental capacity.     

Effects of in vitro maturation of monkey oocytes on their developmental capacity

The study of in vitro maturation (IVM) of rhesus monkey oocytes has important implications for biomedical research and human infertility treatment. In vitro-matured rhesus monkey oocytes show much less developmental potential than IVM oocytes of other species. Since about 1980 when rhesus monkey IVM, in vitro fertilization (IVF) and in vitro embryo culture (IVC) systems were established, numerous efforts have been made to improve the developmental competence of oocytes and to understand the mechanisms regulating oocyte maturation. This review describes recent progress in this area, particularly the effects of factors such as steroid hormones, energy substrates, amino acids, ovarian follicle status, maternal age and breeding season on the developmental competence, gene expression patterns and genome integrity of rhesus IVM oocytes.     

Meiotic competence in horse oocytes: interactions among chromatin configuration, follicle size, cumulus morphology, and season

Horse oocytes were collected from an abattoir over a 15-mo period. After classification of follicle size and cumulus morphology, oocytes were either fixed immediately (0 h) or matured in vitro (24 h). There was no effect of season on the number of antral follicles present on the ovaries, or on oocyte maturation rate for any class of oocyte. The proportion of oocytes having condensed chromatin at 0 h increased with increasing follicle size. The oocyte maturation rate also increased with follicle size, and for follicles 相似文献   

Influence of the dominant follicle on oocytes from subordinate follicles

As the oocyte grows within the follicle, a number of factors influence its health and developmental competence. These factors include follicle size, day of estrous cycle, level of atresia and influence of other follicles such as the dominant follicle. Follicles were dissected from ovaries of synchronized dairy cows on four days during the estrous cycle, and the oocyte from each follicle collected, matured, fertilized and cultured singly until Day 8. Development to blastocyst was greater in oocytes collected during phases of follicular growth than those collected during phases of follicular dominance (P<0.001) over all follicle size categories. Oocyte competence tended to increase with increasing follicle size (P<0.1). Follicular cells analyzed by flow cytometry showed an increase in proportion of apoptotic cells in subordinate follicles during the dominant phase compared to growth phase (P<0.05). Thus, the dominant follicle on both oocyte competence and levels of atresia. Further studies on the effect of dominance has shown that lactate production in cumulus-oocyte-complexes (COCs) from medium-sized follicles collected during a dominance phase and small follicles collected during a growth phase are no different from other follicles, despite having significantly lower uptake of glucose (P<0.1). Thus, COCs from different follicle subclasses differ in their nutrient requirements, and current IVM technology needs further improvement to better assist those oocytes that are developmentally challenged.