Beneficial influence of Vero cells on in vitro maturation and fertilization of bovine oocytes

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.

In vitro embryo production efficiency in cattle and its association with oocyte adenosine triphosphate content, quantity of mitochondrial DNA, and mitochondrial DNA haplogroup

Mitochondria have a broad range of functions that affect reproduction, and structural as well as quantitative variation in mtDNA has been associated with gamete quality and reproductive success. To investigate the mitochondria effect on in vitro embryo production, we collected oocytes by ultrasound-guided follicular aspiration from donor cows known to differ in the developmental capacity, measured by the blastocyst formation rate, of their oocytes. To evaluate the potential effects of mtDNA and mitochondrial function on oocyte quality, the donor cows' mtDNA control region was sequenced and, after pairwise comparisons of polymorphisms, animals were grouped into two major haplogroups. The number of mtDNA molecules per oocyte was quantified by real-time PCR, and the adenosine triphosphate (ATP) content was measured in each oocyte to identify variations between haplogroups. Overall, ATP stocks in oocytes of the two haplogroups differed significantly (P < 0.05; means +/- SEM) both at the germinal vesicle and metaphase II stages (2.8 +/- 0.06 pmol vs. 2.6 +/- 0.07 pmol and 2.9 +/- 0.1 pmol vs. 2.3 +/- 0.06 pmol, respectively). The proportion of development to blastocyst was significantly different between haplogroups (22.3 +/- 2.1 % vs. 36.7 +/- 2.9 %). The number of mtDNA molecules per oocyte was highly variable (377 327 +/- 14 104, ranging from 2.0 x 10(3) to 1.2 x 10(6)) but not significantly different between the two haplogroups; significant differences were observed between animals without any apparent relationship to blastocyst production. These data suggest that mitochondria and mtDNA haplogroup affect the developmental capacity of bovine oocytes in vitro.

Preliminary results on variability in oocyte recovery and developmental competence in cattle derived from embryonic cloning: work in progress

To investigate female gamete developmental competence and variability in cloned cattle, we performed ovum pick-up and in vitro fertilization in four sets of cloned heifers (n = 10, two sets of triplets and two sets of twins), and four groups of non-genetically related control animals (n = 13). A total of 304 OPU were performed and 1798 oocytes were recovered. Mean oocyte production per female per OPU (+/-S.D.) was similar for clone or control animals (5.7+/-2.9 versus 6.1+/-4.5, respectively), however, in two sets of clones variance for the number of oocytes recovered differed significantly (7.1 versus 23.9 and 7.3 versus 26.7, respectively P<0.001) between clone groups and their respective controls, cloned animals being more homogenous. After in vitro maturation, fertilization with semen from the same bull, and culture, the proportion of oocytes from cloned animals that developed into blastocysts was 35.0+/-29.2% and was not significantly different from controls (29.4+/-30.9). The CV for oocyte recovery, and blastocyst rates was lower in all groups of cloned animals than in controls. Nevertheless, within each set of clones, CV values indicated some degree of variability between animals, thus confirming that cloned cattle are not the exact phenotypic copy of each other. Despite the large number of oocytes analyzed, results should be interpreted with caution due to the limited number of cloned animals.

Improvement of development of vitrified two-cell mouse embryos by vero cell coculture

PURPOSE

The purpose of this study was to determine the developmental potential of two-cell mouse embryos resulting from vitrification could increased using monolayer of Vero cells.

METHODS

Two-cell mouse embryos were divided into vitrified and nonvitrified groups. Embryos in the vitrified group were frozen with a combination of 10% ethylene glycol, 30% ficoll, and 0.5% M sucrose (EFS10) as cryoprotectants, and thawed rapidly with 0.5 M sucrose. The survived embryos were cultured either with Vero cells monolayer or in T6 medium. Accordingly the embryos of the nonvitrified group were also cultured. The rates of the development in all the groups were daily determined and statistically compared. At the end of the cultivation period, several expanded blastocysts from each group were stained with ethidium bromide and the mean number of the blastomers were counted and statistically compared.

RESULTS

After 4 days of culture, the developmental potential of vitrified-thawed embryos were significantly reduced in Vero cell-free medium, and the mean cell number of embryos reaching the expanded blastocyst stage were also lower than that of nonvitrified embryos. With exception of last day of culture, Vero cell coculture, resulted in a significant increase in the rate of development of vitrified-thawed embryos as well as improved the mean cell number of expanded blastocysts. On the other hand, the mean cell number of expanded blastocysts of nonvitrified group was significantly improved in coculture group. However, the rate of embryo development except for the first day of culture was similar to that of medium alone.

CONCLUSIONS

The developmental potential of vitrified-thawed embryos appears to be retarded in conventional medium and Vero cell monolayer is capable to eliminate the postthaw deleterious effect of vitrification during the first 3 days of cultivation, but not for a longer period.

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.