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  • Author: P. Mermillod x
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H. Khatir, C. Carolan, P. Lonergan and P. Mermillod

The aims of the present study were to characterize the follicular fluid from prepubertal calf follicles of known size and quality and to study the ability of follicular fluid to support cytoplasmic maturation of calf and cow oocytes. Follicular fluid was obtained from 67 calf follicles classified according to size (S: small < 6 mm, M: medium 6–8 mm and L: large > 8 mm in diameter) and quality (HY: healthy, EA: early atretic and A: atretic). Quality was first determined by mitosis:pycnosis ratios in granulosa cell smears and confirmed by insulin-like growth factor binding protein (IGFBP) patterns. There was approximately 90% agreement between the two methods of follicle classification and on this basis the calf follicular fluid was pooled into nine groups. The accuracy of this pooling was confirmed by evaluation of oestradiol concentrations in the nine pools of follicular fluid using radioimmunoassay. Increases in follicle size were characterized by a decreased intensity of bands for IGFBP-2, IGFBP-5 and IGFBP-4, an increase in the proportion of healthy follicles and a decrease in the proportion of follicles in the early stages of atresia. This finding is in agreement with previously published results in cows. All classes of calf follicular fluid contained lower concentrations of oestradiol than previously reported for corresponding classes of cow follicular fluid. Cow oocytes were matured in M199 alone, or supplemented with 10% fetal calf serum (FCS), or 10% calf follicular fluid from one of three pools (LHY, LEA, LA), fertilized, and cultured for 8 days in synthetic oviduct fluid. Addition of FCS or calf follicular fluid to cow oocytes during in vitro maturation increased the yield of blastocysts on day 8 over the control (23%, 21/91), FCS (39%, 37/96, P < 0.05), LA (41% 21/52, P < 0.05), LEA (32%, 28/88), LHY (36%, 32/88), although not significantly in all cases. The rate of hatching of blastocysts was also improved: control (38%, 8/21), FCS (54%, 20/37), LA (62%, 13/21), LEA (75%, 21/28, P < 0.02), LHY (59% 19/32). In contrast, the addition of either FCS, calf follicular fluid or cow follicular fluid did not improve development of calf oocytes compared with the unsupplemented control. In conclusion, it is probable that serum and follicular fluid contain factors that stimulate the acquisition by oocytes, during maturation, of developmental competence and to which prepubertal oocytes are unable to respond. Specific receptors for these factors may develop only around puberty.

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P. Lonergan, H. Khatir, C. Carolan and P. Mermillod

The aims of the present study were to assess the effect of various substances on meiotic resumption and subsequent development to the blastocyst stage of bovine oocytes. Immature cumulus–oocyte complexes were cultured for 24 h in (a) Medium 199 (M199) alone, or M199 supplemented with (b) 10% fetal calf serum (FCS), (c) 1 μg cycloheximide ml−1, (d) 2 mmol 6-dimethylaminopurine (6-DMAP) l−1, or (e) 0.1 mmol vanadate l−1. After 24 h, groups (a) and (b) were inseminated with frozen–thawed spermatozoa and subsequently cultured, while groups (c–e) were washed and cultured for a second 24 h in M199 + FCS, after which they were inseminated and cultured. At all time points a representative sample of oocytes were fixed and stained with orcein to observe the nuclear status, while others were labelled with [35S]methionine to study protein biosynthesis. Incubation with 6-DMAP, cycloheximide or vanadate completely blocked germinal vesicle breakdown with most oocytes remaining at the germinal vesicle stage after 24 h culture (89%, 100% and 85%, respectively). This inhibitory effect was fully reversible in the case of 6-DMAP and cycloheximide; after a second period of incubation, germinal vesicle breakdown occurred in almost all cases (99% and 100%, respectively), and most reached metaphase II (85% and 83%, respectively). In contrast, inhibition with vanadate was only reversible in 56% of oocytes, with only 6% reaching metaphase II. Cleavage rates at 72 h after insemination and blastocyst yields on day 8 of culture were, respectively: (i) M199, 72% and 34%; (ii) M199 + FCS, 80% and 45%; (iii) M199 + cycloheximide, 81% and 19%; (iv) M199 + 6-DMAP, 77% and 14%. 6-DMAP did not modify methionine incorporation. However, cycloheximide completely blocked protein synthesis when present during the period of labelling. Addition of epidermal growth factor to cycloheximide-inhibited oocytes was without effect. In contrast, epidermal growth factor overcame the effect of 6-DMAP in about 50% of oocytes, resulting in lower developmental rates after IVF. These results give an indication of the feasibility of in vitro meiotic inhibition as a tool in the study of the mechanisms involved in acquisition of competence.

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JJ Dufour, Y Cognie, P Mermillod, JC Mariana and RF Romain

Endocrine control of follicular growth was studied in mature Romanov ewes carrying (RF+) or not carrying (R+2) the Booroola Fec gene during an oestrous cycle after gonadotrophin-dependent follicles were suppressed by treatment with an antagonist of GnRH (Antarelix, 0.5 mg per day) and superovulatory treatment was administered. The left ovary was removed after 10 days of treatment (saline or Antarelix) and the right ovary was removed at the end of the superovulatory treatment. Ewes of both genotypes treated with Antarelix had lower plasma LH concentrations than did controls from day 0 to day 10. The inhibitory effect of Antarelix on LH concentration increased with day of treatment. The variability in FSH concentrations during the initial 10 days was reduced by Antarelix treatment in both genotypes. Plasma FSH concentrations were higher in RF+ ewes than in R+2 ewes. In both genotypes, FSH concentrations varied significantly with day of treatment, with the lowest concentrations at day 8 and the highest concentrations at day 5. RF+ ewes had a greater total and atretic number of antral follicles 0.62-1.12, 1.12-2.00 and 2.00-3.00 mm in diameter (classes 2, 3 and 4) than did R+2 ewes before and after superovulatory treatment. After superovulatory treatment, the total number of atretic and non-atretic follicles > 3.00 mm in diameter (class 5) increased in both genotypes. Superovulatory treatment also increased the number of total and atretic class 4 follicles in RF+ only. Conversely, superovulatory treatment decreased the mean number of class 3 follicles in both genotypes, while the number of atretic follicles was decreased only in R+2 ewes. Antarelix treatment significantly reduced the percentage of follicles > 2.00 mm in diameter in RF+ but not in R+2 ewes. Antarelix treatment before superovulatory treatment increased the total number of class 4 follicles in both genotypes but the increase was more significant in RF+ than in R+2 ewes. These results indicate that Antarelix pretreatment favours a greater superovulatory response in Romanov ewes carrying the Fec gene because ovulatory follicles are recruited from a wider range of follicular size classes.

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P. Mermillod, C. Wils, A. Massip and F. Dessy

Summary. On four occasions ovaries from a total of 35 cows were collected separately at the abattoir where they had been killed. The age of 20 of these cows was recorded. Oocytes from these ovaries were collected separately and were submitted to in vitro maturation, in vitro fertilization and in vitro culture procedures. Ovaries of 34 randomly chosen cows were pooled and treated as the control. Ova from individual cows were cultured in 10 μl droplets and those from pooled ovaries were cultured in groups of 50 in 50 μl droplets of oviductal cell-conditioned medium. The 35 cows treated individually supplied 493 oocytes (mean 14·1 oocytes per cow) with high individual variation (sd = 10·0; range = 0–38) and 47 expanded blastocysts (9·5% of oocytes; mean 1·3 blastocysts per cow; range = 0–6). Among these cows, 16 produced one or more blastocysts. Considerable variation in average development rates was detected over the four replicate experiments (11·3, 4·0, 9·0 and 13·5%). The 34 cows treated as the control supplied 397 oocytes (mean 11·7 oocytes per cow) and 44 expanded blastocysts (11·1% of oocytes; mean 1·3 blastocysts per cow) with high variations between replicates (11·1, 4·0 and 18·1%). No difference was observed between individual and pooled ovaries regarding either the number of oocytes, the rate of blastocyst formation, or the number of blastocysts per cow. No effect of age was detected.

The conclusion was that culture of zygotes in small groups does not impair bovine embryo development in vitro but that high individual variation in oocyte number and the rate of embryonic development may explain the variable results observed in this study between replicate experiments and in general in bovine IVF. These variations will impair the prediction of blastocyst production from individual cows of high genetic value.

Keywords: in vitro fertilization; cow; embryo; blastocyst; breeding; oviduct; conditioned medium

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A. Massip, P. Mermillod, C. Wils and F. Dessy

Blastocysts derived from bovine zygotes fertilized and matured in vitro and cultured for 7 days in conditioned medium were frozen in 1.36 mol glycerol l−1 and 0.25 mol sucrose l−1. In vitro survival after thawing was unaffected by dilution rate in 0.25 mol sucrose l−1. The proportion of blastocysts that re-expanded after 24 h was 81% (70 of 86) and 47% (33 of 70) hatched. Seven pregnancies beyond 2 months resulted from transfer of 21 blastocysts to 19 recipients. Total embryonic loss was 46.2%, of which 31% occurred between days 21 and 35. In vitro survival after thawing was influenced by culture conditions, the best being culture with oviduct epithelial cells, where 55–82% of blastocysts re-expanded, of which 41–54% hatched. Conditioned medium also supported re-expansion, but low hatching (6%), whereas M199 plus fetal calf serum allowed only limited re-expansion (19–40%). This behaviour was not a consequence of freezing. It is suggested that blastocysts produced in vitro have reduced metabolic activity leading to high embryonic loss before or just at the time of implantation and that oviduct cells create a favourable environment after thawing, allowing hatching in vitro.

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F. Revel, P. Mermillod, N. Peynot, J. P. Renard and Y. Heyman

The developmental competence of oocytes from 3-month-old calves was studied through in vitro maturation, fertilization and culture up to the blastocyst stage and by embryo transfer into a foster mother. Oocytes were recovered from antral follicles of calves after or without ovarian stimulation with exogenous FSH and their developmental potential was compared with that of oocytes recovered from cow ovaries. Fertilization and cleavage rates from calf oocytes did not differ significantly from those of cow oocytes. However, after 7 days of culture, the blastocyst formation rate was significantly lower for calves (9% and 11% for nontreated and treated animals, respectively) than for cows (over 20%). Transfer of blastocysts obtained from calf oocytes resulted in a lower pregnancy rate (1 of 23 recipients; 4%) than that achieved with cow oocytes (10 of 26; 38%). The recipient cow that was pregnant from calf embryos delivered a full-term live calf. These data show that some key regulative event that determines the ability to form blastocysts in cattle has not been fully achieved in oocytes from 3-month-old calves.

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B Oussaid, P Lonergan, H Khatir, A Guler, D Monniaux, JL Touze, JF Beckers, Y Cognie and P Mermillod

A GnRH antagonist (Antarelix) was used to suppress endogenous pulsatile secretion of LH and delay the preovulatory LH surge in superovulated heifers to study the effect of a prolonged follicular phase on both follicle and oocyte quality. Oestrous cycles were synchronized in 12 heifers with progestagen (norgestomet) implants for 10 days. On day 4 (day 0 = day of oestrus), heifers were stimulated with 24 mg pFSH for 4 days and luteolysis was induced at day 6 with PGF2 alpha (2 ml Estrumate). Animals in the control group (n = 4) were killed 24 h after the last FSH injection. At this time, heifers in group A36h (n = 4) and group A60h (n = 4) were treated with 1.6 mg of Antarelix every 12 h for 36 and 60 h, respectively, and then killed. After dissection of ovarian follicles, oocytes were collected for individual in vitro maturation, fertilization and culture; follicular fluid was collected for determination of steroid concentrations, and granulosa cells were smeared, fixed and stained for evaluation of pycnosis rates. Granulosa cell smears showed that 90% of follicles were healthy in the control group. In contrast, 36 and 58% of the follicles in group A36h showed signs of early or advanced atresia, respectively, while 90% of the follicles in group A60h showed signs of late atresia. Intrafollicular concentrations of oestradiol decreased (P < 0.0001) from healthy follicles (799.14 +/- 40.65 ng ml-1) to late atretic follicles (3.96 +/- 0.59 ng ml-1). Progesterone concentrations were higher (P < 0.0001) in healthy follicles compared with atretic follicles, irrespective of degree of atresia. Oestradiol:progesterone ratios decreased (P < 0.0001) from healthy (4.58 +/- 0.25) to late atretic follicles (0.07 +/- 0.009). The intrafollicular concentrations of oestradiol and progesterone were significantly higher (P < 0.0001) in the control than in the treated groups. The oestradiol:progesterone ratio was higher (P < 0.0001) in the control (4.55 +/- 0.25) than in the A36h (0.40 +/- 0.05) and A60h (0.07 +/- 0.009) groups. Unexpectedly, the cleavage rate of fertilized oocytes, blastocyst rate and number of cells per blastocyst were not significantly different among control (85%, 41% and 95 +/- 8), A36h (86%, 56% and 93 +/- 5) and A60h (88%, 58% and 79 +/- 4) groups. In addition, there were no significant differences in the blastocyst rates from oocytes derived from healthy (45%), early atretic (54%), advanced atretic (57%) and late atretic follicles (53%). In conclusion, the maintenance of the preovulatory follicles in superovulated heifers with a GnRH antagonist induced more atresia and a decrease in oestradiol and progesterone concentrations. However, the developmental potential in vitro to day 8 of the oocytes recovered from these atretic follicles was not affected.

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A Vitorino Carvalho, E Canon, L Jouneau, C Archilla, L Laffont, M Moroldo, S Ruffini, E Corbin, P Mermillod and V Duranthon

During the last few years, several co-culture systems using either BOEC or VERO feeder cells have been developed to improve bovine embryo development and these systems give better results at high oxygen concentration (20%). In parallel, the SOF medium, used at 5% O2, has been developed to mimic the oviduct fluid. Since 2010s, the SOF medium has become popular in improving bovine embryo development and authors have started to associate this medium to co-culture systems. Nevertheless, little is known about the putative benefit of this association on early development. To address this question, we have compared embryo transcriptomes in four different culture conditions: SOF with BOEC or VERO at 20% O2, and SOF without feeders at 5% or 20% O2. Embryos have been analyzed at 16-cell and blastocyst stages. Co-culture systems did not improve the developmental rate when compared to 5% O2. Direct comparison of the two co-culture systems failed to highlight major differences in embryo transcriptome at both developmental stages. Both feeder cell types appear to regulate the same cytokines and growth factors pathways, and thus to influence embryo physiology in the same way. In blastocysts, when compared to culture in SOF at 5% O2, BOEC or VERO seems to reduce cell survival and differentiation by, at least, negatively regulating STAT3 and STAT5 pathways. Collectively, in SOF medium both blastocysts rate and embryo transcriptome suggest no influence of feeder origin on bovine early development and no beneficial impact of co-culture systems when compared to 5% O2.