Kinetics of first polar body extrusion and the effect of time of stripping of the cumulus and time of insemination on developmental competence of bovine oocytes

Oocyte Selection for In Vitro Embryo Production in Bovine Species: Noninvasive Approaches for New Challenges of Oocyte Competence

Simple Summary

The efficiency of producing embryos using in vitro technologies in cattle species remains lower when compared to mice, indicating that the proportion of female gametes that fail to develop after in vitro manipulation is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting embryo production, the precise identification of noninvasive markers that predict oocyte competence is of major interest. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, a large slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better embryonic development. In addition, the combination of oocyte and zygote selection, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in vitro technologies in livestock species.

Abstract

The efficiency of producing embryos using in vitro technologies in livestock species rarely exceeds the 30–40% threshold, indicating that the proportion of oocytes that fail to develop after in vitro fertilization and culture is considerably large. Considering that the intrinsic quality of the oocyte is one of the main factors affecting blastocyst yield, the precise identification of noninvasive cellular or molecular markers that predict oocyte competence is of major interest to research and practical applications. The aim of this review was to explore the current literature on different noninvasive markers associated with oocyte quality in the bovine model. Apart from some controversial findings, the presence of cycle-related structures in ovaries, a follicle size between 6 and 10 mm, large number of surrounding cumulus cells, slightly expanded investment without dark areas, large oocyte diameter (>120 microns), dark cytoplasm, and the presence of a round and smooth first polar body have been associated with better competence. In addition, the combination of oocyte and zygote selection via brilliant cresyl blue (BCB) test, spindle imaging, and the anti-Stokes Raman scattering microscopy together with studies decoding molecular cues in oocyte maturation have the potential to further optimize the identification of oocytes with better developmental competence for in-vitro-derived technologies in livestock species.

Influence of the duration of in vitro maturation and gamete co-incubation on the efficiency of in vitro embryo development in Italian Mediterranean buffalo (Bubalus bubalis)

The aim of this study was to investigate the effect of the duration of oocyte in vitro maturation (IVM) and gamete co-incubation on the in vitro embryo (IVEP) production efficiency in River buffalo. In Experiment 1, abattoir-derived cumulus oocyte complexes were fixed at 0, 3, 6, 9, 12, 15, 18, 21 and 24 h after the start of in vitro maturation to study the kinetics of nuclear maturation. In Experiment 2, cumulus oocyte complexes were fertilized in vitro following in vitro maturation for 18, 21, 24, 27 or 30 h. After 20 h of gamete co-incubation, presumptive zygotes were denuded and cultured in vitro in synthetic oviduct fluid (SOF) medium. In Experiment 3, following in vitro maturation and fertilization, presumptive zygotes were removed from fertilization drops at 8, 12, 16 and 20 h post-insemination (pi) and placed in culture as described above. Representative samples of oocytes were fixed at 4, 8, 12, 16 and 20 h to evaluate the sperm penetration rate and the incidence of polyspermy at different co-incubation times. The main conclusions of the study are that: (1) the majority of buffalo oocytes accomplish nuclear maturation between 21 and 24 h after the start of in vitro maturation; (2) both cleavage and blastocyst rates linearly decrease with increasing duration of in vitro maturation (from 18 to 30 h); (3) sperm-oocyte incubation for at least 16 h is required for maximum blastocyst yields.

Effect of duration of in vitro maturation on nuclear maturation and fertilizability of feline oocytes

This study was conducted to improve in vitro production of embryos from domestic cats using TCM-199 as an IVM medium. The time sequence of nuclear maturation and the optimal timing of in vitro insemination were examined. Most oocytes were at the germinal vesicle stage immediately after collection; however, 8.3% had already resumed meiosis before IVM culture. After 30 h of IVM culture, the percentage of oocytes at metaphase II (MII) reached a peak (75.5%) and did not change (P>0.05) from 30 to 48 h after IVM culture. The percentage of oocytes with two pronuclei was higher (P<0.05) for oocytes matured for 30 and 36 h (38.2 and 33.0%, respectively) than for those after IVM culture for only 24 h (18.5%). Total sperm penetration rate was highest (P<0.05) for oocytes that had been matured for 30 h (46.1%). After 30 h of IVM and 18 h of IVF culture, 66.3 and 24.8% of inseminated oocytes had cleaved and developed to the blastocyst stage, respectively. We concluded that IVM of feline oocytes for 30 h in TCM-199 resulted in optimal nuclear maturation and sperm penetration.

The effects of duration of in vitro maturation of bovine oocytes on subsequent development, quality and transfer of embryos

We examined the effects of IVM duration on rates of Korean Native Cow (KNC) first polar body extrusion, embryo development and offspring. Cumulus oocytes complexes were cultured in vitro for up to 24h. Extrusion of the first polar body was highest at 16h. At selected times during IVM, oocytes were fertilized and in vitro development was compared to blastocysts collected from superovulated KNC. After fertilization, the cleavage rate did not differ for oocytes with different durations of IVM, but the development rates of the 8-cell and blastocyst stages were significantly higher in IVM 18-h than other durations. The mean inner cell mass, trophectoderm and total cell numbers of in vivo blastocysts (40.0+/-3.8, 87.5+/-3.5 and 127.5+/-1.6, respectively) were similar to those for IVM 18-h group. When in vitro- and in vivo-derived blastocysts were transferred to Holstein heifer recipients, pregnancy and abortion rates did not differ among treatments. Mean gestation length was significantly shorter for in vivo-derived blastocysts than those derived from oocytes with 24h of IVM. Birth weight produced by the IVM 24-h group (32.0+/-2.2kg) was significantly higher than that of in vivo and IVM 18-h groups. The sex ratio of calves was similar between the in vivo and the IVM 24-h group, but all calves derived from the IVM 18-h group were males. Therefore, duration of bovine oocyte IVM played a critical role in embryo development and blastocyst cell number. In addition, it also affected birth weight and sex ratio.

Growth hormone insufficiency and its impact on ovarian function

Growth hormone (GH) and the insulin-like growth factor-I (IGF-I) play significant roles in pubertal development, menarche, the menstrual cycle, fertility, and reproduction. Growth hormone deficiency or insufficiency causes a delay in the onset of puberty and in its normal course unless treated with synthetic GH. It seems that GH affects the ovary during puberty both indirectly through the gonadotropins and IGF-I, and directly through its effect on steroidogenesis. The GH axis is activated by small increases in circulating estrogens, which initiate large increases in GH during puberty. The reproductive function of the female is also affected by GH. GH acts on the ovary affecting gametogenesis and steroidogenesis. GH receptor mRNA and protein have been found in ovarian cells, and this suggests that the direct action of GH provides an important modulatory effect on gonadotropin-dependent and -independent functions. It also affects the maturation of the follicle and gamete, and thereby plays a facilitatory role in fertility. The majority of women with GH-deficiency, but not all, require assisted reproductive technologies to induce ovulation. Many women with polycystic ovary syndrome (PCOS) have an impaired GH response to stimulation with Levo-Dopa and GH releasing hormone (GHRH). Hyperandrogenism in PCOS may contribute to the reduced GH secretion because testosterone directly stimulates somatostatin release. Reduction of the excessive androgens facilitates the dopaminergic control of GH. In conclusion, GH-insufficient states disrupt ovarian function, causing problems in sexual maturation, the menstrual cycle, and the reproductive ability of the female.

Analysis of differential maternal mRNA expression in developmentally competent and incompetent bovine two-cell embryos

The main objective of this study was to identify mRNA transcripts associated with embryonic developmental competence. In cattle, mRNA transcripts, ribosomes, and proteins accumulated during the growth phase are drawn on to sustain maturation, fertilization, and the initial cell cycle divisions up to the 8- to 16-cell stage. Early cleaving mammalian zygotes are more likely to develop to the blastocyst stage than their later cleaving counterparts, thus reflecting the intrinsic quality of the oocytes from which they originated. We describe the combination of this well-established model for the retrospective determination of developmental competence in mammalian oocytes with a technique for wide screening of differential gene expression in different biological populations. Immature cumulus oocyte complexes were recovered from surface visible follicles on abattoir ovaries, washed, and submitted to routine in vitro maturation and fertilization. Two-cell embryos were removed from culture at 3-hr intervals from 24 to 42 hr post insemination (pi). Two populations of two-cell embryos were identified; those that cleaved early (before 27 hpi) and those that cleaved late (after 33 hpi). Suppressive subtractive hybridization was carried out on cDNA from the two populations, following which, differentially expressed amplicons were subcloned and sequenced. The sequences were submitted to the nonredundant and expressed sequence tag (EST) databases at NCBI using the BLAST algorithm. The differential expression of three selected candidate genes that were identified as putatively upregulated in the early cleaving zygotes were chosen for further investigations; histone H3, cyclin B1, and GDF-9B. Using quantitative real time PCR we have shown that histone H3A is significantly more abundant in embryos that cleave earliest.

Fertilization of mouse oocytes from in vitro-matured preantral follicles using classical in vitro fertilization or intracytoplasmic sperm injection

Early preantral mouse follicles with a diameter of 110-160 microm were cultured in vitro for 10 or 12 days. Mature oocytes were retrieved following hCG, and fertilization was attempted either by in vitro fertilization (IVF) or intracytoplasmic sperm injection (ICSI). Two-cell and blastocyst formation rates and blastocyst cell numbers were compared between 10-day and 12-day in vitro-matured oocytes versus in vivo-matured oocytes. Uncleaved IVF oocytes were subjected to chromosome analysis. The 2-cell formation rate was significantly improved by ICSI compared with IVF both in 10-day (72.1% versus 56.1%; P = 0.03) and 12-day cultures (74.1% versus 54.5%; P = 0.028). Cytogenetic analysis of uncleaved MII oocytes following IVF showed that about 30% of MII oocytes showed no sign of sperm penetration. The blastocyst formation rate was significantly lower in 12-day versus 10-day cultures, whether fertilization was by IVF (40.7% versus 62.4%, P = 0.016) or by ICSI (32.5% versus 57.1%, P = 0.035). Blastocyst cell numbers from IVF and ICSI 10-day groups were similar and both significantly higher (P < 0.001) than from IVF 12-day cultures. All above expressed values were significantly higher for in vivo-matured oocytes. In conclusion, fertilization of oocytes from in vitro-matured mouse preantral follicles can be optimized with ICSI, giving significantly higher 2-cell formation rates than IVF. Blastocyst formation rate was not influenced by the technique of fertilization but rather by the extent of the in vitro culture period. Best results on preimplantation development of oocytes for in vitro-matured preantral follicles were obtained with ICSI on oocytes from 10-day in vitro cultures.

Optimization of in vitro bovine embryo production: effect of duration of maturation, length of gamete co-incubation, sperm concentration and sire

The aim of these experiments was to investigate the effect of duration of IVM, duration of gamete co-incubation, and of sperm dose on the development of bovine embryos in vitro. In addition, the speed of sperm penetration of six bulls of known differing in vivo and in vitro fertility was examined. In Experiment 1, following IVM for 16, 20, 24, 28 or 32 h, cumulus oocyte complexes (COCs) were inseminated with 1 x 10(6) spermatozoa/ml. After 24 h co-incubation, presumptive zygotes were denuded and placed in droplets of synthetic oviduct fluid (SOF). In Experiment 2, following IVM and IVF, presumptive zygotes were removed from fertilization wells at 1, 5, 10, 15 or 20 h post insemination and placed in culture as described above. In Experiment 3, following IVM, COCs were inseminated with sperm doses ranging from 0.01 x 10(6) to 1 x 10(6) spermatozoa/ml. Following co-incubation for 24 h, presumptive zygotes were placed in culture as described above. In Experiment 4, following IVM, oocytes were inseminated with sperm from six bulls of known differing field fertility. To assess the rate of sperm penetration, oocytes were subsequently fixed every 3 h (up to 18 h) following IVF. Based on the results of Experiment 4, in Experiment 5, following IVM for 12, 18 or 24 h, COCs were inseminated with sperm from two sires with markedly different penetration speeds. After 24 h co-incubation, presumptive zygotes were denuded and placed in culture. The main findings from this study are that (1) the optimal duration of maturation of bovine oocytes in vitro to maximize blastocyst yield is 24 h, (2) sperm-oocyte co-incubation for 10 h is sufficient to ensure maximal blastocyst yields, (3) sperm concentrations of 0.25 x 10(6) and 0.5 x 10(6) spermatozoa/ml yielded significantly more blastocysts than any other concentration within the range of 0.01 x 10(6) 1 x 10(6) spermatozoa/ml, (4) there are marked differences in the kinetics of sperm penetration between sires and this may be a useful predictor of field fertility, and (5) the inferior development associated with slower penetration rates may in part be overcome by carrying out IVF at a time when the actual penetration is most likely to coincide with the completion of maturation.

Effect of urea during in vitro maturation on nuclear maturation and embryo development of bovine cumulus-oocyte-complexes

High concentrations of urea in reproductive tract fluids are detrimental to bovine reproduction. Therefore, in experiment 1, the effect of 6 mM urea on nuclear maturation of cumulus-oocyte-complexes (COC) collected from abattoir ovaries was studied. After 4, 8, 12, 16, 20, and 24 h of in vitro maturation, the nuclear stages of samples of the COC were determined. During the first 8 h of maturation, germinal vesicle breakdown and chromosome condensation, resulting in the metaphase I stage, occurred at higher rates in the presence of urea. Segregation of the chromatids and extrusion of the polar body seemed to be impaired in the presence of urea, resulting in a higher percentage of oocytes arrested in metaphase I or telophase, and a lower percentage of oocytes in metaphase II after 24 h of maturation. Overall, nuclear progression of COC matured in the presence of urea differed from COC matured in control medium. In experiment 2, COC were matured for 24 h either in the presence or absence of 6 mM urea followed by in vitro fertilization and culture. After fertilization, a sample of the COC was fixed and stained to determine the fertilization rate. The cleavage rate was determined 3 d after start of maturation, and the stage of embryonic development was recorded 7 and 9 d after start of maturation. Based on cultured oocytes, urea in the maturation medium decreased the subsequent percentage of fertilization, cleavage, and development on d 7 and 9 (43.2, 56.1, 14.8, and 18.2%, respectively for urea vs. 64.1, 68.8, 22.4, and 23.9%, respectively for the control group). Embryonic development as a percentage of cleaved oocytes was not significantly affected by urea. Therefore, negative effects of urea were evident primarily during oocyte maturation and fertilization.

The promotory effect of growth hormone on the developmental competence of in vitro matured bovine oocytes is due to improved cytoplasmic maturation

In a previous study we have shown that the addition of growth hormone (GH) during in vitro maturation accelerates nuclear maturation, induces cumulus expansion, and promotes subsequent cleavage and embryonic development. The aim of this study was to investigate whether the promotory effect of GH on subsequent cleavage and blastocyst formation is due to an improved fertilization and whether this effect is caused by an improved cytoplasmic maturation of the oocyte. Therefore, bovine cumulus oocyte complexes (COCs) were cultured for 22 hours in M199 supplemented with 100 ng/ml bovine GH (NIH-GH-B18). Subsequently the COCs were fertilized in vitro. Cultures without GH served as controls. To verify whether the promoted fertilization is caused by the effect of GH on cumulus expansion or oocyte maturation, cumulus cells were removed from the oocytes after in vitro maturation (IVM) and denuded MII oocytes were selected and fertilized in vitro. Both IVM and in vitro fertilization (IVF) were performed at 39 degrees C in a humidified atmosphere with 5% CO2 in air. At 18 hours after the onset of fertilization, the nuclear stage of the oocytes was assessed using 4,6-diamino-2-phenylindole (DAPI) staining. Oocytes with either an metaphase I (MI) or MII nuclear stage and without penetrated sperm head were considered unfertilized; oocytes with two pronuclei, zygotes, and cleaved embryos were considered normally fertilized; and oocytes with more than two pronuclei were considered polyspermic. To evaluate cytoplasmic maturation, the distribution of cortical granules 22 hours after the onset of IVM, and sperm aster formation 8 hours after the onset of fertilization were assessed. In addition, to assess the sperm-binding capacity, COCs were fertilized in vitro, and 1 hour after the onset of fertilization the number of spermatozoa bound to the oocytes was counted. The addition of GH during IVM significantly (P < 0.001) enhanced the proportion of normal fertilized oocytes. Removal of the cumulus cells prior to fertilization and selection of the MII oocytes did not eliminate the positive effect of GH on fertilization. No effect of GH on the sperm-binding capacity of the oocyte was observed. In addition, GH supplementation during IVM significantly (P < 0.001) enhanced the migration of cortical granules and sperm aster formation. It can be concluded that the promotory effect of GH on the developmental competence of the oocyte is due to a higher fertilization rate as a consequence of an improved cytoplasmic maturation.

In vitro maturation of bovine oocytes in the presence of growth hormone accelerates nuclear maturation and promotes subsequent embryonic development

Regulatory effect of GH on follicular growth and development in the cow is well documented. The aim of this study was to investigate the role of GH on in vitro bovine oocyte maturation. Therefore bovine cumulus oocyte complexes (COCs) were cultured in M199 without FCS and gonadotropins and in the presence of 10, 100, or 1,000 ng/ml bovine GH (NIH-GH-B18). The COCs were incubated at 39 degrees C in a humidified atmosphere with 5% CO2 in air and nuclear stage was assessed after 2, 4, 8, 16, 22, and 24 hr of incubation using DAPI staining. To assess the effect of GH on developmental capacity of the oocytes, COCs were incubated in the presence of GH for 22 hr, followed by IVF and in vitro embryo culture. Cultures without GH served as controls. For subsequent development, the embryos were cultured in M199 supplemented with 10% FCS on a monolayer of BRL cells. Embryos were scored morphologically and the efficiency of the culture system was evaluated as (1) the percentage of cleaved embryos 4 days after IVF, (2) the percentage of blastocysts on day 9 expressed on the basis of the number of oocytes at the onset of culture, and (3) the percentage of hatched blastocysts on day 11 expressed on the basis of the total number of blastocysts present at day 9. GH (100 and 1,000 ng/ml) significantly accelerated nuclear maturation (P < 0.001). At 4 and 8 h the percentage of oocytes in GV stage after GH treatment (54% and 19%) was significantly lower than the control (64% and 41%). Similarly at 16 and 22 h the percentage of oocytes in MII stage was significantly higher in the GH-treated group; (58% and 77%) and (46% and 62%) for GH and control respectively. The number of oocytes in MII beyond 22 hr of culture did not differ; 100 and 1,000 ng/ml GH induced significant cumulus expansion (P < 0.05), which was not observed in the absence of GH. Addition of 100 and 1,000 ng/ml GH during maturation significantly (P < 0.01) enhanced subsequent cleavage rate from (64% and 67%) in control to (75% and 81%) in GH-treated group; embryonic development in terms of day 9 blastocyst formation was also significantly increased in the presence of GH (29% and 34%) compared to the control (18% and 24%). The hatchability of the blastocysts was not influenced by GH. From the present data, it can be concluded that GH present during IVM has a beneficial effect on subsequent development.