Preimplantation development following in vitro fertilization of mouse oocytes: effects of timing of superovulation and preincubation in vitro

The proteome, not the transcriptome, predicts that oocyte superovulation affects embryonic phenotypes in mice

Superovulation is the epitome for generating oocytes for molecular embryology in mice, and it is used to model medically assisted reproduction in humans. However, whether a superovulated oocyte is normal, is an open question. This study establishes for the first time that superovulation is associated with proteome changes that affect phenotypic traits in mice, whereas the transcriptome is far less predictive. The proteins that were differentially expressed in superovulated mouse oocytes and embryos compared to their naturally ovulated counterparts were enriched in ontology terms describing abnormal mammalian phenotypes: a thinner zona pellucida, a smaller oocyte diameter, increased frequency of cleavage arrest, and defective blastocyst formation, which could all be verified functionally. Moreover, our findings indicate that embryos with such abnormalities are negatively selected during preimplantation, and ascribe these abnormalities to incomplete ovarian maturation during the time of the conventional superovulation, since they could be corrected upon postponement of the ovulatory stimulus by 24 h. Our data place constraints on the common view that superovulated oocytes are suitable for drawing general conclusions about developmental processes, and underscore the importance of including the proteins in a modern molecular definition of oocyte quality.

Effect of Cetrorelix administration on ovarian stimulation in aged mice

In mice, ovarian stimulation via hormone administration is an effective method for obtaining many ova simultaneously, but its effect is reduced by the influence of aging. In this study, we demonstrate that this problem can be improved by administering the gonadotropin-releasing hormone antagonist Cetrorelix prior to ovarian stimulation. Before 12-month-old female mice were injected with 5 IU pregnant mare serum gonadotropin and 5 IU human chorionic gonadotropin, we administered 5 µg/kg Cetrorelix for 7 consecutive days (7 times) or 3 times once every 3 days. As a result, 8.7 ± 1.9 (mean ± SEM, n=10) and 9.8 ± 1.3 (n=10) oocytes were obtained, respectively, as opposed to 4.7 ± 1.2 oocytes (n=9) in the case of no administration. Collagen staining of ovarian tissue showed that Cetrorelix administration reduced the degree of fibrosis, which improved ovarian function. In addition, equivalent fertilization and fetal development rates between control and Cetrorelix-treated aged mouse-derived oocytes were confirmed by in vitro fertilization and embryo transfer (Fertilization rate; control: 92.2% vs. 3 times: 96.9%/7 times: 88.5%, Birth rate; control: 56.4% vs. 3 times: 58.3%/7 times: 51.8%), indicating the normality of the obtained oocytes. It is concluded that Cetrorelix improved the effect of superovulation in aged mice without reducing oocyte quality. This procedure will contribute to animal welfare by extending the effective utilization of aged female breeding mice.

The optimal time for intracytoplasmic sperm injection in the human is from 37 to 41 hours after administration of human chorionic gonadotropin

Fertilization rates increased continuously with the time elapsed after administration of hCG, reaching a peak of 84% when intracytoplasmic sperm injection (ICSI) was performed >41 hours after hCG administration. However, the highest implantation rate, 24%, was achieved when ICSI was performed 37-41 hours after hCG administration.

In vitro fertilization in mice: Strain differences in response to superovulation protocols and effect of cumulus cell removal

Strain differences have proven to be crucial components in mouse in vitro fertilization (IVF) and superovulatory protocols. To maximize the yield of IVF-derived mouse eggs, a series of experiments was conducted using different injection timing intervals for administration of pregnant mare serum gonadotropin (PMSG) and hCG to induce follicular development and ovulation. Strains were chosen that were representative of those commonly used in genetic engineering experimentation. These strains included ICR outbred, C57BL/6 inbred, and B6SJLF1 hybrid (C57BL/6J x SJL/J F1) mice. Females were superovulated using 4 PMSG/hCG/IVF timing regimens (group), with sperm obtained from males of the same strain. Group designations were based on the following PMSG/hCG and hCG/oocyte collection intervals, respectively: Group 1, 55 and 21.5 h; Group 2, 60 and 14.5 h; Group 3, 55 and 14.5 h; Group 4, 48 and 14.5 h. After overnight culture of ova, fertilization rates (development to the 2-cell stage) were assessed. A logistic regression was performed using indicator variables for both strain and group. There was a significant strain influence on ova fertilization rate, based on the coefficients of mouse strain (ICR, beta = -1.1067, P = 8E-17 and C57BL/6, beta = -0.5172, P = 8E-06). Additionally, group affected the proportion of fertilized ova obtained (coefficient of Group 1, beta = -1.3152, P = 0.00 and Group 3, beta = 0.9531, P = 3E-12). From the coefficients for the interaction terms, the effect of groups varies across mouse strain. Therefore, the treatment that produces the highest fertilization rate is related to and contingent upon the strain of mouse. In the second study, the Group 3 protocol was used to evaluate fertilization differences between cumulus-intact and cumulus-free oocytes. Again, there was a significant strain influence on ova fertilization rate based on the coefficients of mouse strain (ICR, beta = -2.6639, P = 0.00; C57BL/6, beta = -2.5114, P = 0.00). However, there was no difference between Cumulus and No Cumulus groups (cumulus coefficient, beta = 0.1640, P = 0.59872), indicating that there was no affect of cumulus presence on fertilization rate. In summary, responses to standardized mouse IVF protocols vary significantly. The efficiency of IVF procedures can be optimized between and within specific mouse strains by the timing of superovulatory regimens. However, absence of cumulus cells during the IVF procedure does not adversely affect fertilization rate.

In vitro fertilization of gonadotropin-stimulated leopard cat (Felis bengalensis) follicular oocytes

Based on techniques developed for the domestic cat, in vitro fertilization (IVF) studies were conducted in the taxonomically related leopard cat (Felis bengalensis). Adult females received pregnant mares' serum gonadotropin (PMSG) followed 80 or 84 h later by human chorionic gonadotropin (hCG) on two to four occasions over a 40-day to 27-month interval. Oocytes were collected laparoscopically from ovarian follicles 25-27 h after hCG and co-cultured with processed, homologous spermatozoa (37 degrees C, 5% CO2 in air, humidified atmosphere) for 30-36 h. There was no apparent ovarian refractoriness to repeated treatments with exogenous gonadotropins. Overall, the mean number of mature follicles present and the total number of oocytes and proportion of immature oocytes collected did not differ (P greater than 0.05) between the 80 h (4.9 +/- 0.9; 4.7 +/- 1.2; 14.9%, respectively) and 84 h (5.6 +/- 1.4; 5.4 +/- 1.7; 22.2%, respectively) gonadotropin interval groups. However, the proportion of mature leopard cat oocytes fertilized in vitro, as determined by embryonic cleavage, was increased (P less than 0.005) by extending the interval between PMSG and hCG from 80 (17.5%) to 84 (52.4%) h. These data 1) demonstrate that, compared to the domestic cat, the ovaries of the leopard cat are less responsive to a given PMSG/hCG treatment; 2) indicate that leopard cat follicular oocytes can be recovered readily by laparoscopy and are capable of becoming fertilized in vitro; and 3) suggest that IVF may be a viable approach for producing embryos and perhaps enhancing captive propagation of rare Felidae.

Tripling of serum progesterone (P4) and embryonic morphological features in conception and nonconception cycles, after human in vitro fertilization

A series of 26 in vitro fertilization (IVF) cycles was studied for changes of serum progesterone levels before and after injection of human chorionic gonadotropin (hCG) by a comparison of the number of follicles punctured, number of oocytes recovered, morphological features of oocytes, fertilization rate, cleavage rate, and quality of embryos before their transfer. Subjects were further divided into three groups according to their pregnancy outcome. Five pregnancies were generated and reached the stage of clinical confirmation of live baby delivery or live fetus by ultrasound scanning of the uterine contents. Six patient cycles that had a prolonged luteal phase and beta-hCG levels greater than 40 MIU/ml were described as biochemical pregnancies. Fifteen patient cycles showed no sign of pregnancy. The significant finding of this study is related to the serum progesterone level increase from 20 to 34 hr after hCG injection. The nonpregnancy group yielded a 1.2-fold increase compared with the biochemical pregnancy and pregnancy groups, which had a 3-fold increase. The usage of this multiple effect of progesterone may aid in the prediction of the "high-quality embryo" that might result from a given treatment cycle, indicate the completion of luteinization, the proper timing of hCG to induce final oocyte maturation, and the necessary length of preincubation, and aid in the prediction as to whether or not a pregnancy is likely to result.

Effects of high-dose and multiple-dose gonadotropin stimulation on mouse oocyte quality as assessed by preimplantation development following in vitro fertilization

The effects of increasing the level of ovarian stimulation on preimplantation embryonic development were assessed using a mouse in vitro fertilization system. When F1 hybrid (C57BL/6 X CBA/Ca) mice received a single injection of 5 IU pregnant mare's serum gonadotropin (PMSG) followed 60 hr later by 5 IU human chorionic gonadotropin (hCG) approximately 50% of the resultant postovulatory oocytes developed to the blastocyst stage following in vitro fertilization. Increasing the single dose of PMSG to 10 or 15 IU resulted in significant reductions in the frequency of development to the blastocyst stage. When one or two additional doses of 5 IU PMSG were administered 24 and 48 hr after an initial injection of 5 IU, lower frequencies of oocytes with the potential for full preimplantation development were again observed. This reduction in gamete quality was significantly greater when the final dose of PMSG was administered only 12 hr prior to hCG. The results suggest that excessive gonadotropin stimulation may compromise the quality of the preimplantation embryos obtained following in vitro fertilization and that the timing of gonadotropin administration may also be critical.