Evaluation of culture systems containing bovine oviduct epithelial cells or granulosa cells to mature and maintain the developmental competence of bovine oocytes in vitro

Effect of ammonium chloride on the growth and metabolism of bovine ovarian granulosa cells and the development of ovine oocytes matured in the presence of bovine granulosa cells previously exposed to ammonium chloride

Three experiments determined first, the effect of increasing ammonium chloride (NH(4)Cl) concentrations on the growth and metabolism of bovine granulosa cells isolated from small and medium-sized bovine ovarian follicles; secondly, whether the changes in granulosa cell growth and metabolism induced by NH(4)Cl were reversible; and thirdly, whether granulosa cells, previously conditioned with NH(4)Cl, were able to support maturation of oocytes in vitro. In Experiment 1, using a 2 (follicle size class) x 5 (NH(4)Cl concentration) factorial design, granulosa cells from small or medium-sized ovarian follicles were incubated for 96 h with 0, 0.2, 0.4, 0.8 or 1.6 micromol NH(4)Cl/ml. Experiment 2 used a split plot factorial design where granulosa cells were incubated for 96 h in the presence or absence of 1 micromol/ml NH(4)Cl and then incubated in the absence or presence of 1 micromol/ml NH(4)Cl for a further 48 h. Finally in Experiment 3, ovine oocytes were matured on layers of bovine granulosa cells which had not been conditioned with NH(4)Cl or conditioned with 0.5 or 1.0 micromol/ml NH(4)Cl and development of embryos to the blastocyst stage followed and blastocyst quality assessed. In Experiment 1, incubation of granulosa cells in increasing concentrations of NH(4)Cl reduced cell growth, increased cell protein concentrations and increased the amounts of MTT (3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyltetrazolium bromide) oxidised and oestradiol and progesterone produced per 10(5) cells. Cells from medium-sized follicles were more sensitive to NH(4)Cl concentration and oxidised more MTT and produced less progesterone at high NH(4)Cl concentrations than cells from small-sized follicles. When, in Experiment 2, NH(4)Cl was removed from cell culture after 96 h incubation, cells previously exposed to NH(4)Cl grew at a slower rate during the subsequent 48 h, contained more cellular protein, oxidised more MTT and produced more oestradiol and progesterone than cells not previously exposed to NH(4)Cl. Maturation of ovine oocytes in coculture with bovine granulosa cells not exposed to NH(4)Cl (Experiment 3) increased egg cleavage rate and the proportion of cleaved eggs which developed to the blastocyst stage. Conditioning of granulosa cells with NH(4)Cl supported egg cleavage and development to the blastocyst stage at rates similar to those observed in the absence of granulosa cells. In conclusion, these experiments showed that the in vitro growth and metabolism of granulosa cells were altered by concentrations of NH(4)Cl similar to ammonium ion concentrations measured in follicular fluid and that these effects were not immediately reversible. Furthermore, the ability of granulosa cells conditioned with NH(4)Cl to support in vitro maturation of oocytes was impaired.

Practical measures to improve in vitro blastocyst production in the bovine

Media, chemicals, sera and protocols used for in vitro production of bovine embryos are different from one laboratory to another. This paper describes some of the critical steps required to produce embryos in vitro, suggests quality control measures to lower variations in blastocyst yield and describes different tests which may be used when implementing new procedures in a routine production system.

Evaluation of mitomycin-treated vero cells as a co-culture system for IVM/IVF-derived bovine embryos

Support of the in vitro development of IVM/IVF-derived bovine embryos by Vero cells was evaluated by comparing the following treatment groups: 1) proliferating (Unt-Vero) vs nonproliferating (Mit-Vero) cells; 2) supplementation of medium with estrous cow serum (ECS) vs bovine serum albumin (BSA); 3) Mit-Vero cells vs bovine oviduct epithelial cells (BOECs); and 4) addition of leukemia inhibitory factor (LIF) to Mit-Vero cell co-cultures at Day 1 vs Day 4. Mit-Vero cells stimulated higher rates of blastocysts (Day 7, 40 vs 27%) and hatched blastocyst (Day 10, 38 vs 12%) formation than Unt-Vero cells. These rates were comparable to those obtained with BOECs; blastocyst hatching was slightly higher following co-culture with Mit-Vero cells (36%) than BOECs (29%). Blastocyst formation was similar in ECS- vs BSA-supplemented medium; however, hatching was greatest (37%) during co-culture in medium +10% ECS. While the addition of LIF throughout the co-culture period was ineffective, addition of the cytokine beginning at Day 4 slightly increased blastocyst formation rates. Evaluation of LIF secretion using ELISA revealed detectable levels of the cytokine in Mit-Vero-conditioned medium (50 pg/10(5) cells); this may explain the minimal influence of exogenous LIF during embryo co-culture. Mit-Vero cells provided comparable support of bovine embryo development when used even up to 2 wk after establishment as monolayers. In conclusion, Mit-Vero cells provide a readily-available, safe and easy-to-use co-culture method which is at least as supporting of bovine embryo development as BOECs. One contribution of these cells may be secretion of the cytokine LIF.

Developmental competence of bovine embryos derived from oocytes collected at various stages of the estrous cycle

The developmental competence of bovine oocytes collected from donors at various stages of the estrous cycle and fertilized in vitro was investigated by comparing the yields of embryos obtained from oocytes isolated from the ovaries of cows slaughtered on estrous cycle Days 7 and 14, 8 and 15, 9 and 16 and on Days 19, 20 and 2. The percentages of oocytes that developed into blastocysts at Day 8 after exposure to spermatozoa were: 11.9 vs 20.0; 13.2 vs 30.5; 20.8 vs 29.8; and 11.7, 4.4 and 16.9, respectively. A significantly higher proportion of oocytes developed into blastocysts following isolation on cycle Days 14 to 16 (24.3 %) than following recovery on Days 7 to 9 (13.0 %; P < 0.05), Days 19 to 20 (6.6 %; P < 0.05) or Day 2 (16.9 %; P < 0.05). Embryo development was also faster in oocytes isolated at the end of the luteal phase (Days 14 to 16). These results demonstrate that the stage of the estrous cycle may influence the developmental potential of oocytes and in vitro embryo production.

Presence of granulosa cells during oocyte maturation improved in vitro development of IVM-IVF bovine oocytes that were collected by ultrasound-guided transvaginal aspiration

The effects of granulosa cells in maturation media on male pronuclear formation and in vitro development of in vitro-matured and fertilized (IVM-IVF) bovine oocytes were examined. In Experiment 1, cumulus-oocyte complexes (COCs) were aspirated from follicles of slaughterhouse ovaries and classified into 4 morphological categories according to the surrounding cumulus cells: Grade 1 (> 4 layers), Grade 2 (3 to 4 layers), Grade 3 (1 to 2 layers) and Grade 4 (denuded). Oocytes were co-cultured with or without granulosa cells (1 x 10(6) cells/ml) for 21 to 22 h. At 18 and 192 h after insemination, the abilities of oocytes to form a male pronucleus and develop up to the blastocyst stage in vitro were determined, respectively. The presence of granulosa cells during maturation did not affect (P < 0.05) the ability of oocytes in Grades 1 and 2 to form a male pronucleus and to develop to the blastocyst stage in Grades 1 and 4. However, the incidence of male pronuclear formation in Grades 3 and 4 and in vitro development to the blastocyst stage in Grades 2 and 3 was higher (P < 0.05) when COCs were cultured in the presence of granulosa cells than when cultured in the absence of granulosa cells. In Experiment 2, COCs collected by ultrasound-guided aspiration were co-cultured with or without granulosa cells, fertilized and cultured as described above. The incidence of blastocysts at 192 h after insemination was higher (P < 0.05) when COCs were cultured for maturation in the presence of granulosa cells (24%) than in the absence of granulosa cells (12%). These results demonstrate that supplementation of maturation medium with granulosa cells improves the quality of oocytes with relatively few cumulus cell layers, as determined by male pronuclear formation and in vitro development. We also conclude that this supplementation effectively improves the developmental ability of bovine IVM-IVF oocytes that were collected by ultrasound-guided transvaginal aspiration.