Effect of IGFBP-4 during In Vitro Maturation on Developmental Competence of Bovine Cumulus Oocyte Complexes

Insulin-like growth factors (IGFs) are essential for oocyte maturation. Their bioavailability is regulated by their respective binding proteins (IGFBPs) and proteases. IGFBP-4 blocks the biological effects of IGFs. High IGFBP-4 expression has been associated with follicle atresia. We hypothesized that IGFBP-4 affects oocyte developmental competence during maturation. Therefore, the aim of this study was to examine the effect of IGFBP-4 on the developmental rate of bovine cumulus-oocyte complexes (COCs) during in vitro embryo production. Abattoir-derived COCs were matured with rbIGFBP-4 (2000, 540, and 54 ng/mL) compared to a control. Cumulus expansion, oocyte maturation, cleavage, blastocyst, and hatching rates were evaluated. Furthermore, blastocyst gene expression of SOCS2, STAT3, SLC2A1, SLCA3, BAX, and POU5F1 transcripts were quantified using RT-qPCR. No statistical differences were detected among the groups for cumulus expansion, maturation, cleavage, blastocyst rates, or all gene transcripts analyzed. However, at day 8 and 9, the number of total hatching and successfully hatched blastocysts was lower in 2000 ng/mL rbIGFBP-4 compared to the control (day 8: total hatching: 17.1 ± 0.21 vs. 31.2 ± 0.11%, p = 0.02 and hatched blastocyst 6.7 ± 0.31 vs. 21.5 ± 0.14%, p = 0.004; day 9 total hatching 36.4 ± 0.18 vs. 57.7 ± 0.10%, p = 0.009 and hatched blastocyst 18.2 ± 0.21 vs. 38.1 ± 0.11%, p = 0.004). We concluded that high concentrations of rbIGFBP-4 might negatively affect the subsequent ability of the embryo to hatch and possibly compromise further elongation.

Melatonin improves rate of monospermic fertilization and early embryo development in a bovine IVF system

The developmental competence of male and female gametes is frequently reduced under in vitro conditions, mainly due to oxidative stress during handling. The amino-acid derived hormone melatonin has emerged as a potent non-enzymatic antioxidant in many biological systems. The goal of the present study was to evaluate the effects of melatonin on post-thaw sperm quality, fertilizing ability, and embryo development and competence in vitro after in vitro fertilization. Frozen-thawed bovine spermatozoa were incubated either in the presence of 10⁻¹¹ M melatonin (MT), or its solvent (ethanol; Sham-Control), or plain Tyrode’s Albumin Lactate Pyruvate medium (TALP, Control). Computer-Assisted Sperm Analysis (CASA) and flow cytometry data after 30 min, 120 min, and 180 min incubation did not reveal any significant effects of melatonin on average motility parameters, sperm subpopulation structure as determined by hierarchical cluster, or on the percentage of viable, acrosome intact sperm, or viable sperm with active mitochondria. Nevertheless, in vitro matured cumulus-oocyte-complexes fertilized with spermatozoa which had been preincubated with 10⁻¹¹ M melatonin (MT-Sperm) showed higher (P < 0.01) rates of monospermic fertilization, reduced (P < 0.05) polyspermy and enhanced (P < 0.05) embryo development compared to the Control group. Moreover, the relative abundance of MAPK13 in the in vitro-derived blastocysts was greater (P < 0.05) than observed in the Control group. In conclusion, adding melatonin to the sperm-preparation protocol for bovine IVF improved proper fertilization and enhanced embryonic development and competence in vitro.

Melatonin enhances in vitro developmental competence of cumulus-oocyte complexes collected by ovum pick-up in prepubertal and adult dairy cattle

Bovine oocytes from prepubertal donors have been used for in vitro embryo production to decrease the generation interval. However, reduced cumulus-oocyte competence, mainly attributed to increased apoptosis, has been observed in oocytes/embryos collected from prepubertal donors. Here, we investigated the effects of the potent antioxidative molecule melatonin on cumulus-oocyte competence and embryo development in prepubertal and adult dairy cattle in vitro. A total of fifteen Holstein Friesian calves, six to ten months old (7.6 ± 1.34 months of age). And fifteen adult cows with one to four calvings (2.3 ± 0.96 calvings) were enrolled as ovum pick up (OPU) donors in this study. Cumulus-oocyte complexes (COCs) were cultured either in the presence or absence of melatonin (0.01 nM). The proportion of cleavage stages, blastocysts, and advanced blastocysts was determined. Embryo quality was assessed via differential staining to determine the total embryonic cells and allocation to the inner cell mass (ICM) and trophectoderm (TE) cells. Melatonin treatment yielded a greater percentage of blastocysts compared to the control group, i.e. oocytes from both adult cows (P = 0.0485; 24.8 ± 3.5% vs. 16.0 ± 3.4%, respectively), and from prepubertal donors (P = 0.0007; Melatonin 23.1 ± 5.1% vs. Control: 11.1 ± 3.5%). Adult cows had significantly (P = 0.0370) greater advanced blastocyst rates than those found in the prepubertal group (13.9%± vs. 7.0±%, respectively). Additionally, the number of ICM, total cells, and the ratios ICM: Total, ICM: TE, respectively, were greater (P < 0.05) after melatonin treatment compared with the control group (39.1 ± 2.8, 98.6 ± 5.7, 0.4 ± 0.01, and 0.7 ± 0.04 vs. 27.3 ± 2.9, 81.2 ± 5.8, 0.34 ± 0.01, and 0.52 ± 0.04, respectively). Blastocysts derived from adult cows had a greater number of TE (P = 0.01) and total embryonic cells (P = 0.0095) compared to the prepubertal donor group (63.5 ± 3.2 and 101.05 ± 4.8 vs. 48.9 ± 4.3 and 78.8 ± 6.5, respectively). Nevertheless, embryonic cell counting in embryos derived from prepubertal COCs equated to that observed from adult donors after melatonin exposure. In conclusion, these results indicate that the presence of melatonin during in vitro maturation improves cumulus-oocyte competence, embryo development, and quality by increasing the allocation of embryonic cells to the ICM compartment and the total number of embryonic cells in both adult and prepubertal bovine donors.