Effects of canine serum collected from dogs at different estrous cycle stages on in vitro nuclear maturation of canine oocytes

Canine oocytes are ovulated at prophase of the first meiotic division and undergo maturation in the distal part of the oviduct for at least 48-72 h. Because of these differences from other domestic mammals, the efficiency of in vitro maturation (IVM) of canine oocyte is very low. The present study was conducted to evaluate the effects of canine serum on IVM of canine oocytes recovered from ovaries in various reproductive states (follicular, luteal or anestrous stages). Oocytes were recovered by mincing ovaries from bitches presented for ovariohysterectomy at various stages of the estrous cycle. Heat-inactivated canine serum was prepared with blood taken from dogs at the anestrous, estrous or diestrous stage of the estrous cycle as determined by progesterone concentration and vaginal cytology. Oocytes were cultured for 72 h in tissue culture medium (TCM)-199 supplemented with 10% canine anestrous, estrous or diestrous serum or fetal bovine serum (FBS) (experiment 1), or supplemented with 0 (control), 5%, 10% or 20% canine estrous serum (experiment 2). In experiment 1, IVM of oocytes collected at the follicular stage of the estrous cycle to metaphase II (MII) stage was higher (p < 0.05) with canine estrous serum (14.2%) than with canine anestrous (5.2%) or diestrous serum (6.3%), FBS (2.2%) or in the control (2.2%). In experiment 2, oocytes collected at the follicular stage of the estrous cycle cultured in TCM-199 with 10% canine estrous serum showed a higher maturation rate to MII stage (13.5%, p < 0.05) compared with those cultured with 5% (1.3% MII) or 20% canine estrous serum (5.1% MII) or the control (2.7% MII). In conclusion, our results demonstrate that supplementing culture medium with 10% canine estrous serum improves IVM of canine follicular stage oocytes.     

Germinal vesicle chromatin configuration and meiotic competence is related to the oocyte source in canine

This study investigated the effect of deriving oocytes from different stages of the estrous cycle on oocyte diameter, germinal vesicle (GV) chromatin configuration, and in vitro meiotic competence in canine oocytes. Cumulus oocyte complexes (COCs) were recovered from both ovaries during anestrous, follicular, and luteal phases and in vivo ovulated oocytes. The diameter of canine oocyte was compared with or without the zona pellucida (ZP) before in vitro maturation (IVM). Also, GV chromatin configuration was evaluated before (0 h) or 72 h after IVM by fixation with 3.7% formaldehyde supplemented with 10 microg/ml Hoechst 33342 for 30 min. COCs were matured in TCM199 supplemented with 10% fetal bovine serum (FBS), 0.6 mM cysteine, 0.2 mM pyruvic acid, 50 microg/ml gentamycin sulfate, and 20 microg/ml 17beta-estradiol (E(2)) at 39 degrees C and 5% CO(2) in air for 72 h. The diameter of in vivo ovulated oocytes with the ZP (167.5+/-12.7 microm) or without ZP (133.9+/-5.3 microm) was significantly greater (p<0.05) than those of anestrous, follicular, and luteal oocytes (with ZP, 151.2+/-7.4, 153.1+/-8.8 and 152.8+/-5.4 microm, respectively; without ZP, 115.3+/-7.6, 122.1+/-4.9 and 114.3+/-6.6 microm, respectively). At 0 h, the GV-II configuration was more prevalent in oocytes from anestrual ovaries than from follicular or luteal ovaries or in vivo ovulated oocytes (63.6% versus 14.8%, 33.0%, and 0.0%; p<0.05), whereas the proportion of oocytes with the GV-V configuration was higher in follicular phase and ovulated oocytes than in oocytes from anestrus and luteal phase (57.4% and 100% versus 2.0% and 22.7%; p<0.05). However, oocytes in luteal phase exhibited diverse GV configurations (10.3%, 33.0%, 16.5%, 13.4%, and 22.7% in GV-I, GV-II, GV-III, GV-IV, and GV-V, respectively). After 72 h post-IVM, a greater percentage of in vivo ovulated oocytes progressed to MII than those oocytes collected during anestrous, follicular, and luteal phases (50.0% versus 5.5%, 11.5%, and 9.1%; p<0.05). In conclusion, the oocyte diameter, GV chromatin configuration, and meiotic maturation of canine COCs are related to the oocyte source. These results indicated that the oocyte source could be critical to nuclear progression to MII stage in canines.     

Epidermal growth factor can be used in lieu of follicle-stimulating hormone for nuclear maturation of porcine oocytes in vitro

Epidermal growth factor (EGF) has been considered a potential regulator of meiotic and cytoplasmic maturation in mammalian oocytes, but inconsistencies exist between earlier studies, probably due to differences in the culture conditions used. Using a serum- and hormone-free in vitro maturation (IVM) medium, this study investigated the specific contribution of EGF on IVM of porcine (Sus scrofa) oocytes and its interactive effects with follicle-stimulating hormone (FSH), porcine follicular fluid (pFF), cumulus cells, and serum. It was noteworthy that EGF functionally mimicked the action of FSH and could completely replace FSH for nuclear maturation (83.2 ± 4.4% vs. 55.9 ± 5.2%; mean ± SEM), whereas EGF had a synergistic effect with FSH on cytoplasmic maturation of porcine oocytes (P < 0.05). Specific inhibition of EGF receptor (EGFR) by tyrphostin AG 1478 inhibited both EGF- and FSH-induced meiotic resumption (17.9 ± 5.2% and 18.2 ± 4.4%, respectively), thereby suggesting that EGFR signaling pathway was essential for oocyte reentry into the meiotic cell cycle. Furthermore, it is possible that FSH action occurs via the EGFR signaling pathway to induce meiotic maturation, although alternate pathways could not be excluded. There were also individual or combined effects of cumulus cells, FSH, serum, and pFF with EGF on IVM of porcine oocytes (P < 0.05). Although FSH had a synergistic effect with EGF on cytoplasmic maturation, pFF masked the effects of EGF on both nuclear and cytoplasmic maturation of porcine oocytes (P < 0.05). Moreover, the presence of cumulus cells was essential for EGF action. In conclusion, a defined system was used to better examine the effects of EGF. We inferred that EGF functionally mimics FSH for nuclear maturation of porcine oocytes, and its exogenous supplementation into IVM medium can optimize the beneficial effects of FSH on cytoplasmic maturation of oocytes to obtain enhanced embryo development in vitro.     

Effect of co-culturing with embryonic fibroblasts on IVM, IVF and IVC of canine oocytes

We studied the effects of mouse embryonic fibroblasts (MEF) and canine embryonic fibroblasts (CEF) on IVM, IVF and IVC of canine oocytes. Cumulus-oocyte complexes were harvested from ovaries by slicing, and in vitro maturation was evaluated in three different conditions: culture media only (control), co-culture with MEF, or co-culture with CEF. The oocytes were cultured for 48 or 72 h. Only oocytes larger than 100 microm in diameter with a homogeneous dark cytoplasm and two or more layers of cumulus cells were used. The culture medium was TCM 199+10% fetal bovine serum (FBS) with 100 IU/mL penicillin and 100 microg/mL streptomycin. After 48 h of IVM, the oocytes were fertilized in vitro with fresh canine spermatozoa that had been selected by a swim-up method, and the oocytes and spermatozoa were co-cultured in modified Krebs-Ringer bicarbonate solution (TYH) for up to 20 h in 5% CO2 in air at 38.5 degrees C. After insemination, oocytes were transferred to three different conditions (the same as for IVM) and were cultured. After 48 or 72 h of maturation in vitro, the maturation rate of MII oocytes cultured in co-culture of MEF and CEF was higher than for oocytes cultured in control (P<0.05). Although the rate that reached the MII stage was not different in the 48 and 72 h cultures, the percentage of degenerated oocytes was greater at 72 h in all three treatment groups. The proportion of monospermic and polyspermic oocytes was not different among the three treatment groups. Cleavage rates were higher in the MEF and CEF treatment groups than in the control group (P<0.05). Co-culture with CEF developed the embryo up to the 16-cell stage, and with MEF up to morula stage. In conclusion, co-culture of embryonic fibroblast cells enhanced nuclear and cytoplasmic maturation of canine oocytes.     

Effects of estradiol-17beta and progesterone supplementation on in vitro nuclear maturation of canine oocytes

Unlike in other domestic animals, in vitro maturation (IVM) of canine oocytes has had limited success. The present study investigated the effect of the estrous cycle and estradiol-17beta (E2) or progesterone (P4) supplementation on in vitro nuclear maturation of canine oocytes recovered from domestic dog ovaries in various reproductive states (follicular, luteal or anestrous stages). Oocytes were cultured in serum-free tissue culture medium (TCM)-199 supplemented with various concentrations of E2 (Exp. 1: 0, 0.1, 1.0 or 2.0 microg/ml) or P4 (Exp. 2; 0, 0.5, 1.0 or 2.0 microg/ml) for 72 h to determine the effective concentration of hormones. In Exp. 3, in order to investigate the synergistic effect of E2 and P4 supplementation, three groups of oocytes were cultured with 2 microg/ml E2 plus various concentrations of P4 (0, 0.5, 1.0 or 2.0 microg/ml). As results, the rate of maturation to metaphase II (MII) stage was significantly higher (P < 0.05) in oocytes from the follicular stage supplemented with 2 microg/ml E2 (14.7%) compared to the other groups (1.5-8.2%). Significantly higher (P < 0.05) maturation rate to MII stage was observed in oocytes from the follicular stage supplemented with 1.0 (10.0%) or 2.0 microg/ml (10.8%) P4 compared to the other groups (0-4.8%). Furthermore, more (P < 0.05) oocytes from the follicular stage supplemented with 2.0 microg/ml of E2 and P4 (16.6%) were matured to MII stage compared to oocytes from the follicular stage supplemented with 2.0 microg/ml E2 alone (10.4%) or the other groups of oocytes (0-7.8%). Interestingly, compared to 2.0 microg/ml E2 alone (10.4%), supplementation of 2 microg/ml E2 + 0.5 microg/ml P4 (3.4%) decreased the maturation of oocytes from the follicular stage to MII stage. In conclusion, the present study demonstrated that supplementation of the culture medium with E2 or P4 alone significantly increased maturation of canine oocyte to MII and that P4 supplementation with E2 further promote or decrease oocyte maturation compared to E2 alone depending on P4 concentration.     

Influence of co-culture with oviductal epithelial cells on in vitro maturation of canine oocytes

The process of oocyte maturation in the canine species is unique among mammals: oocytes are immature at ovulation and the resumption and progression of meiotic maturation occur in the oviduct. This study was performed to investigate (i) the effect of co-culture with infundibulum and ampullar oviductal epithelial cells on the in vitro maturation of canine oocytes and (ii) the culture time necessary to reach full meiotic maturation. For this purpose the oocytes, collected from the ovaries of bitches undergoing ovariectomies, were divided into three groups and cultured for 48 and 72 h with the following systems: (A) TCM 199 + 10% oestrus bitch serum + FSH (0.1 IU.mL(-1)), LH (0.1 IU.mL(-1)) + progesterone (1 microg.mL(-1)) + oestradiol (1 microg.mL(-1)) + cysteamine (100 microM); (B) medium A plus infundibulum cells; (C) medium A plus ampullar cells. Infundibulum and ampullar cells were recovered from the oviducts of bitches at the oestrus stage of their cycle. The results showed that after 48 h of incubation, a significantly higher meiotic resumption (P < 0.01) was observed in the oocytes cultured with infundibulum (59%) and ampullar cells (60.0%), than in the control group (40.0%). There was also a significantly (P < 0.01) higher meiotic progression to the MII in systems B and C (15.6% and 16.7%) than in system A (4.0%). After 72 h of culture, the percentages of meiotic resumption and progression were unchanged. These results showed that both the infundibulum and the ampullar oviductal epithelial cells positively influence the meiotic resumption and progression of canine oocytes and that 48 h are sufficient for the completion of nuclear maturation.     

Successful in vitro production of embryos in the red deer (Cervus elaphus) and the sika deer (Cervus nippon)

The aim of our study was to define the conditions for IVM and IVF of oocytes in 2 common deer species as models for endangered related subspecies. Immature oocytes were recovered during the breeding season from postmortem ovaries (red deer) or by repeated laparoscopic follicular aspiration (sika deer). Oocytes were cultured for 24 h in IVM medium supplemented with EGF or FSH and follicular fluid. Stag semen was collected by electroejaculation (both species) or by epididymal flushing (red deer) and cryopreserved. For IVF, oocytes were exposed to different concentrations of thawed spermatozoa in a modified Tyrode albumin lactate pyruvate medium supplemented with 20% (v/v) estrus sheep serum for 18 h. After IVF, presumptive zygotes were allowed to develop in vitro for 7 days in synthetic oviduct fluid (SOF) supplemented with fetal calf serum (10%, v/v). In both species, the presence of ovine FSH and follicular fluid improved the in vitro maturation rate. In the sika deer, the optimal sperm concentration for IVF was 10(6)/mL and some fertilized oocytes reached the early morula stage (20 to 25 cells). In the red deer, after IVF with ejaculated or epididymal spermatozoa (2.0 x 10(6)/mL), 20% of zygotes developed to the blastocyst stage (50 to 80 cells).     

In vitro maturation, in vitro fertilization and embryonic development of canine oocytes

In this study we have investigated the efficiency of in vitro maturation (IVM) as a basic way to study the development of canine oocytes after in vitro fertilization (IVF). We decided, therefore, to perform two-part experiments. Firstly, experiment I compared the effects of TCM199 without fetal bovine serum (FBS) with TCM199 supplemented with 5% FBS on the in vitro nuclear maturation rate of canine oocytes. For the efficiency of meiotic development to the metaphase II (MII) stage, we found that 4.7% (4/64) of all oocytes grown in TCM199 without FBS developed to the MII stage compared with only 1.7% (1/59) of those grown in TCM199 with 5% FBS for 48 h. Therefore, FBS did not increase in vitro nuclear maturation. In experiment II, the cleavage rate of canine oocytes used for IVF was investigated following heparin treatment. Canine oocytes were fertilized in four groups: Fert-TALP medium without heparin (Fert I) or Fert-TALP medium supplemented with 10, 20 or 30 microg/ml heparin (Fert II, Fert III, Fert IV, respectively). Oocytes that were grown for 24 h in Fert I following fertilization showed the highest rate of all of the groups, 6.5% (5/77) and developed to the early morula stage. Markedly, the oocytes cultured in Fert I for 24 h following insemination had a higher rate of embryonic development than other groups. We can assert that, unlike findings in other mammals, heparin treatment in canine IVF does not increase the efficiency of the fertilization rate and is therefore not an important factor.     

Effect of conditioned medium of mouse embryonic fibroblasts produced from EC-SOD transgenic mice in nuclear maturation of canine oocytes in vitro

The rate of in vitro maturation (IVM) of canine oocytes has not improved in comparison to that of other mammalian species. This study aims to improve the efficiency of canine oocytes IVM using the antioxidant, extracellular superoxide dismutase (EC-SOD). Thus, the effect of conditioned medium of EC-SOD transgenic mouse embryonic fibroblasts cultured with MEF culture medium (DMEM + 5% FBS) for in vitro nuclear maturation in canine oocytes was investigated. In experiment I, oocytes were collected from the ovaries of domestic bitches, which were allotted to one of two groups: (1) TCM199 + 1% FBS (n = 108) or (2) DMEM + 5% FBS (n = 112), cultured for 48 h and investigated for in vitro nuclear maturation of canine oocytes using Hoechst staining. Meiotic progression to metaphase II in group 1 was 1.8% compared to 1.8% in group 2. In experiment II, EC-SOD levels were examined in NTg-CMEF and Tg-CMEF at 0, 2 and 4 days obtained from EC-SOD transgenic mice generated in our laboratory. The concentration of EC-SOD in Tg-CMEF at day 2 (371.7 +/- 3.1 ng/ml) was the highest for all groups (P < 0.05). EC-SOD levels in Tg-CMEF were higher than in NTg-CMEF; therefore, the efficiency of Tg-CMEF for IVM was investigated. In experiment III, oocytes were allotted to one of three groups: (1) Tg-CMEF at day 0 (n = 84), (2) Tg-CMEF at day 2 (n = 92) or (3) Tg-CMEF at day 4 (n = 98), cultured for 48 h and the IVM of canine oocytes investigated. The mean percentage of MII oocytes in IVM was 2.4, 4.4 and 2.0% for groups 1, 2 and 3, respectively. In experiment IV, the effects of conditioned medium of EC-SOD transgenic mouse embryonic fibroblasts (Tg-CMEF) cultured in MEF culture medium were compared with conditioned medium acquired from non-transgenic mouse embryonic fibroblasts (NTg-CMEF) on IVM of canine oocytes. In this experiment, meiotic progression to metaphase II was 7.1% in Tg-CMEF versus 0% in NTg-CMEF (P < 0.05). Tg-CMEF was more effective than NTg-CMEF. In conclusion, it was verified that canine oocytes were able to effectively progress to metaphase II in IVM when cultured in Tg-CMEF.     

The effects of bovine serum albumin and fetal bovine serum on the development of pre- and postcleavage-stage bovine embryos cultured in modified CR2 and M199 media

The effects of protein supplementation on bovine embryo development in vitro was evaluated using a 4 × 2 factorial arrangement with ten replications. A total of 6438 oocytes collected from abattoir ovaries were used. Bovine serum albumin (BSA) and fetal bovine serum (FBS) were added in various combinations to simple (modified CR2) and complex (M199) media during culture of precleavage-stage IVM/IVF-derived ova from 18 h after insemination to 72 h and postcleavage-stage embryos after 72 h of culture. Cleavage rates did not differ (p > 0.05) between media supplemented with FBS or with BSA. However, the postcleavage development to the blastocyst stage of in vitro-derived bovine embryos is better in media supplemented with FBS than BSA. A greater (p < 0.05) proportion of cleaved occytes developed to blastocysts and hatched blastocysts in media supplemented with FBS during postcleavage culture. The percentage of embryos that stopped development at the morula stage was significantly (p < 0.05) greater in media supplemented with BSA during postcleavage culture. Viability of blastocysts produced in CR2 and M199 supplemented with FBS were further assessed by transfer to recipients. In CR2, 25 transferred blastocysts resulted in seven pregnancies and the birth of three normal calves. In M199, 24 transferred blastocysts resulted in five pregnancies and the birth of two normal calves. There was no difference (p > 0.05) in rate of embryo development between CR2 and M199.     

In vitro maturation rates of canine oocytes from anoestrous bitches in simple media

The meiotic competence of canine oocytes collected from anoestrous bitch ovaries and cultured for 72 h in different media was studied. The base culture medium was TCM 199 enriched with 10% fetal bovine serum (TCM); the effect of supplementation with EGF (50 ng x mL(-1)) or ITS (insulin: 10 microg x mL(-1); transferrin: 5.5 microg x mL(-1); selenium: 5 microg x mL(-1)) was also studied. TCM was also compared to a Synthetic Oviductal Fluid (SOF). All the media contained FSH (0.1 UI x mL(-1)), LH (10 UI x mL(-1)), 17beta-oestradiol (4 microg x mL(-1)) and kanamycin. Despite the anoestrous stage of the donor bitches, resumption of meiosis occurred in a high proportion of the oocytes, (mean value 77.3%). The number of oocytes showing the 'germinal vesicle breakdown' nuclear stage was not influenced by the type of the culture medium used. ITS had a positive effect on nuclear progression to later stages (from metaphase I to metaphase II); however, this effect was not statistically significant.     

In vitro maturation of canine oocytes co-cultured with bovine and canine granulosa cell monolayers

The present study investigated the effects of bovine granulosa cell monolayers (BGML) and canine granulosa cell monolayers (CGML) on nuclear maturation of canine oocytes with and without cumulus cells. Cumulus-oocyte complexes (COCs) or cumulus-free oocytes were cultured in Dulbecco's Modified Eagle's Medium (DMEM, control group), DMEM with BGML (BGML group), or DMEM with CGML (CGML group) for 72 h at 38.5 °C in 5% CO₂, 5% O_2, and 90% N₂. All media were supplemented with 10% of FCS, 50 ng/mL of EGF, 2 μg/mL of estradiol-17β, 0.1 IU/mL of hCG, 0.1 IU/mL of FSH, 0.25 mM of pyruvic acid, 100 μM of β-mercaptoethanol, 100 IU/mL of penicillin, and 100 μg/mL of streptomycin. In cumulus-enclosed oocytes retrieved from ovaries at estrus and/or diestrus, the highest percentage of M-II oocytes (P < 0.05) was present in the BGML group (27.0%) compared with the CGML group (7.9%) and the control group (3.5%). In cumulus-free oocytes collected from ovaries at estrus and/or diestrus, the proportions of M-II oocytes co-cultured with the CGML were low (3.0%) and similar (P > 0.05) to proportions achieved with control (3.0%). However, the presence of BGML improved (P < 0.05) the ability of denuded oocytes to develop into M-II (10.2%). The BGML group had the highest overall meiotic resumption (P < 0.05), and least oocyte degeneration (P < 0.05) among experimental groups. In conclusion, BGML had a positive impact on the in vitro maturation system, as well as meiotic resumption of canine oocytes.     

In vitro maturation of bitch oocytes from advanced preantral follicles in synthetic oviduct fluid medium: serum is not essential

The ability of oocytes from preantral follicles to mature in vitro was assessed using a synthetic oviduct fluid (SOF) medium. Advanced preantral follicles (approximately 210 microm diameter) were isolated from the ovaries of domestic bitches and assigned to one of four treatment groups: (1) SOF (n = 230); (2) SOF + 3 mg/ml bovine serum albumin (+BSA, n = 220); (3) SOF + 20% fetal bovine serum (+FBS, n = 227); or (4) SOF + 3 mg/ml BSA + 20% FBS (+BSA+FBS, n = 232), then cultured for up to 72 h. A group of control follicles was not cultured (n = 103). The percentages of oocytes reaching metaphase I to metaphase II stages (MI to MII) did not differ between treatments at each culture period. Within treatments, the percentages of oocytes at MI to MII stages did not differ with duration of culture. However, when compared to the control group (0.97%) the percentages of oocytes at MI to MII increased (P < 0.05) in the SOF group after 48 h (10.0%) and 72 h (12.2%) of culture. In the +BSA (10.1%) and +FBS (9.7%) groups, the percentages of oocytes at MI to MII increased (P < 0.05) above control values only after 72 h of culture. The percentage of oocytes at MI to MII did not significantly increase in the +BSA+FBS group (3.9,6.6 and 7.6% at 24,48 and 72 h of culture, respectively) compared to the control group. These results indicate that under the described conditions supplementation of culture medium with BSA or FBS is not essential, and the simple medium SOF can support nuclear maturation of a small proportion of bitch oocytes in vitro.     

Effect of growth factors, EGF and IGF-I, and estradiol on in vitro maturation of sheep oocytes

The objective of these experiments was to determine the effect of exogenous addition of insulin-like growth factor-I (IGF-I, 100 ng/mL), epidermal growth factor (EGF, 10 ng/mL) and estradiol (E2, 100 ng/mL) to the maturation medium of sheep oocytes on their subsequent development in vitro. Addition of IGF-I to the maturation medium did not improve nuclear or cytoplasmic maturation of sheep oocytes at the concentration tested. However, EGF improved significantly the resumption of meiosis (84% oocytes in metaphase II stage after IVM vs. 59% in medium alone). Cleavage rate and blastocyst development rates were improved (P<0.01) after addition of EGF (60% and 29%, respectively), as compared with maturation in TCM 199 alone (39% and 19%, respectively), but remained lower than rates observed after maturation in complete medium containing follicular fluid (FF, 10%) and FSH (81% and 35%, respectively). No additive effect of EGF over FSH was observed during these experiments. Addition of FF to FSH containing maturation medium improved significantly both cleavage (P<0.001) and blastocyst rates (P<0.05). Addition of E2 to the IVM medium is not required when medium already contains FF. However, in defined conditions supplementation of maturation medium with E2 had a positive effect. These results suggest that EGF, FSH and E2 may play an important role in the nuclear and cytoplasmic maturation of sheep oocytes in vitro.     

Assessment of canine oocyte viability after transportation and storage under different conditions

To improve assisted reproductive technologies in the domestic dog, different transport treatments were evaluated for their ability to maintain viability of canine oocytes, as assessed by esterase activity 8h after storage or after 48 h of in vitro maturation (IVM) culture. In Experiment 1, ovaries were transported within reproductive tracts or were excised and stored at either 20 or 37 degrees C in phosphate buffered saline. Oocytes collected from reproductive tracts transported at 37 degrees C had the greatest viability after storage (P<0.05). However, after IVM there were no significant differences among any of the four storage conditions in oocyte viability or meiotic resumption (P=0.05). In Experiment 2, isolated oocytes were transported in either TCM-199 with Hank's salts and Hepes buffer or in TL-Hepes at either 20 or 37 degrees C, or in maturation medium equilibrated with 5% CO(2) at 37 degrees C. In Experiment 2, oocytes transported in Hepes buffered media at 37 degrees C had greater viability rates after storage than did those transported in these same media at 20 degrees C or in sodium bicarbonate buffered medium at 37 degrees C (P<0.001). After IVM, oocytes transported in the 37 degrees C treatment groups had greater viability rates than did those transported at 20 degrees C (P<0.01). Overall, isolated oocytes transported at 37 degrees C had greater rates of meiotic resumption than did those transported at 20 degrees C (P<0.05). Taken together, these data indicate that canine oocytes exhibited sensitivity to lesser temperatures and maintained greater rates of viability during transport at 37 degrees C. Isolated oocytes maintained greater viability than oocytes transported in situ. Hepes buffered media increased viability rates for isolated oocytes transported at 37 degrees C compared to a similar medium buffered with sodium bicarbonate.     

Meiotic competence of bovine fetal oocytes following in vitro maturation

The in vitro ability between fetal and cow oocytes to resume meiosis and progression to metaphase-II (M-II) was compared. Cumulus oocyte complexes (COCs) were harvested from 2 to 6 mm follicles from ovaries of 7.5 month to term fetuses and adult cows. Cumulus cells were removed using 3 mg/ml hyaluronidase and repeated pipetting. Denuded oocytes were fixed in 3% glutaraldehyde, stained with DAPI and evaluated under fluorescent microscopy for nuclear status before in vitro maturation (IVM). COCs from fetal and adult ovaries were also matured in 200 microl droplets of medium 199 supplemented with 10 microg/ml FSH, 10/ml LH, 1.5 microg/ml estradiol, 75 microg/ml streptomycin, 100 IU/ml penicillin, 10 mM hepes and 10% FBS for 24 h at 39 degrees C and 5% CO(2). Matured oocytes were fixed, stained and evaluated as explained above for nuclear status namely stage of germinal vesicle (GV) development and subsequent meiotic competence. Data were analyzed using chi-square analysis. The majority of fetal oocytes (P<0.05) before IVM were at GV stages GV-I (27.7%), GV-II (37.6%) and GV-V (22.8%) compared to cow oocytes, which were at GV stages IV (28.3%) and V (46.7%). After IVM, fewer fetal oocytes were at earlier stages of GV development and majority (P<0.05) were at GV-V (24.0%), premetaphase (17.4%) and metaphase-I (M-I: 7.2%) stages. However, after IVM, more cow oocytes matured to M-II than did fetal oocytes (93.7% versus 26.9%; P<0.05). In conclusion, fetal oocytes do not mature in vitro as well as cow oocytes. Our findings suggest that the low meiotic competence of fetal oocytes can be attributed to their being at earlier stages of GV development before IVM.     

Size of the donor follicle, but not stage of reproductive cycle or seasonality, influences meiotic competency of selected domestic dog oocytes

Ability of ovarian oocytes from the domestic dog to complete nuclear maturation in vitro (IVM) varies markedly among donors and generally is 20% or less of all oocytes cultured. To identify the cause(s) underlying these significant variations in meiotic maturation (to metaphase II; MII), we retrospectively analyzed data from 1,643 oocytes recovered from 90 bitches for which stage of reproduction and season of year were known. Neither stage of reproduction (proestrus/estrus, diestrus, anestrus, or prepuberty) nor season (P > 0.05) influenced the ability of oocytes to achieve nuclear maturation in vitro. A second study was conducted to examine the impact of follicular size on meiotic maturation. Populations of large oocytes were recovered from four categories of follicles (ranging from <0.5 to > 2 mm in diameter) and cultured in TCM 199 for 48 hr. Follicular size influenced (P < 0.05) meiotic competence. Mean percentages of MII oocytes were 16.9 +/- 9.2, 26.1 +/- 7.6, 38.4 +/- 9.2, and 79.5 +/- 10.9 for oocytes recovered from < 0.5 mm, > or = 0.5-< 1 mm, 1-2 mm, and > 2 mm diameter follicles, respectively. In summary, stage of reproduction and season have no impact on the ability of dog oocytes to achieve nuclear maturation in vitro. However, we demonstrated for the first time that dog oocytes acquire meiotic competency during follicular development. IVM success of selected oocytes from large size follicles (almost 80%) is about 60% higher than measured in most previous studies involving randomly collected oocytes.     

Embryonic development of in vitro matured and in vitro fertilized dog oocytes

In several studies, early cleavage stage canine embryos have been derived from in vitro fertilized oocytes cultured under various conditions. Despite these results, IVF protocols for canine oocytes have yielded low fertilization rates. In this study, Experiment I compared the effects of tissue culture medium (TCM)-199 supplemented with either (A) 1 microg/ml estradiol or (B) 20 microg/ml estradiol + 1 microg/ml human somatotropin (hST) on the in vitro nuclear maturation rate of canine oocytes. Meiotic progression to the metaphase I and II (MI/MII) stages at 72 hr of in vitro culture (IVC) was 10.2% (11/108) in medium A versus 14.1% (30/142) in medium B (P = 0.802). In Experiment II, cleavage rate was determined among oocytes recovered from ovaries of bitches at different reproductive stages. Oocytes (n = 888) were retrieved from bitches at the follicular, anestrous, and luteal stages and selected for high morphological quality. Oocytes were matured for 48 hr in TCM-199 supplemented with 1 microg/ml hST + 20 microg/ml estradiol. Oocytes were in vitro fertilized with fresh canine spermatozoa that had been isolated on a Percoll gradient, and were cultured in synthetic oviduct fluid (SOF) medium with bovine serum albumin (BSA; 4 mg/ml) up to 5 days in 5% CO(2) in air at 37 degrees C. A proportion of oocytes (30.6%) with identifiable nuclear material had cytoplasm penetrated or fertilized by sperm. The percentage of oocytes developing into early stage embryos was 10.1% (27/267). Although pronuclear development was observed to be higher for oocytes recovered at the follicular phase, the cleavage rate was similar among oocytes recovered from bitches at the follicular, anestrus, and luteal stages. There was no correlation between the proportion of capacitated or acrosome reacted spermatozoa and pronuclei formation and/or percent cleavage. It was concluded that TCM-199 supplemented with 1 microg/ml hST and estradiol (20 microg/ml) supports nuclear and cytoplasmic maturation of canine oocytes. In this study, meiotic competence was verified by the in vitro production (IVP) and development of embryos up to the 8 cell-stage. Furthermore, the results indicate that, under the described conditions and despite the influence of reproductive status of the bitch on the developmental competence of in vitro fertilized oocytes to the pronuclei stage, cleavage was independent of donor's reproductive estrous cycle stage.     

Influence of follicular components on oocyte meiosis in vitro

Oocytes and follicular components obtained from ovaries recovered from mature Hereford cows at slaughter were used to determine follicular influence on oocyte maturation. Some oocytes were fixed immediately to determine the stage of maturation. The remaining oocytes were cultured for 32 to 34 hr in various environments to determine the influences of the granulosum and follicular fluids on meiotic changes. All noncultured oocytes had dictyate nuclei except one in premetaphase. Oocytes cultured in 50 or 100% follicular fluid or in contact with stratum granulosum cells showed some meiotic inhibition both before and after germinal vesicle breakdown (GVB). The least resumption of meiosis occurred in oocytes cultured in their intact follicles.     

Effects of thiol compounds on in vitro maturation of canine oocytes collected from different reproductive stages

Various thiol compounds are known to improve cytoplasmic and/or nuclear maturation of oocytes in vitro. The present study examined the effects of two thiol compounds, cysteine (0.1, 0.5, and 1.0 mM) and cysteamine (50, 100, and 200 microM), on cytoplasmic and nuclear maturation of canine oocytes. Oocytes collected from different reproductive stages were cultured in TCM-199 supplemented with 10% fetal bovine serum, 2.2 mg/ml sodium carbonate, 2.0 microg/ml estrogen, 0.5 microg/ml FSH, 0.03 IU/ml hCG, and 1% penicillin-streptomycin solution for 72 h. Data were analyzed by two-way ANOVA after arcscine transformation and protected by Bonferroni post hoc test. The effects of cysteine and cysteamine on canine IVM were varied depending on the reproductive stage of oocyte donor bitches. In the follicular stage, significantly more oocytes reached the metaphase II (M II) stage when cultured with 0.5 or 1.0 mM cysteine (16.7% and 16.9%, respectively) compared to the control (6.2%). In the follicular stage, cysteamine increased oocyte maturation rate upto the M II stage (15.1% to 17.0%) compared to the control (4.4%). Both the 0.5 mM cysteine and 100 microM cysteamine, alone or together, increased the intracellular GSH level of canine oocytes compared to the control. Irrespective of reproductive stage, no further beneficial effects on nuclear or cytoplasmic maturation were observed when 0.5 mM cysteine and 100 microM cysteamine were supplemented together. In conclusion, addition of 0.5 mM cysteine and 100 microM cysteamine to the maturation medium improved IVM of canine oocytes.