Investigation into developmental potential and nuclear/mitochondrial function in early wood and plains bison hybrid embryos

Effect of cortisol on bovine oocyte maturation and embryo development in vitro

Glucocorticoids (GCs) are important mediators of key cellular events. Herein, we investigated the effect of adding cortisol to the IVM medium on the acquisition of developmental competency in bovine oocytes. Cortisol (0.01, 0.1, or 1 μg/mL) had no effect on cleavage rates or cell numbers of resulting blastocysts; however, supplementation with 0.1 μg/mL during IVM increased blastocyst rates of in vitro-fertilized bovine oocytes as compared to untreated controls (41 ± 10% vs. 21 ± 1.2%, P < 0.05, respectively). This concentration was chosen to assess changes in the relative expression of potential GC target genes. Oocytes matured in the presence of cortisol and their corresponding cumulus cells did not show changes in expression for genes analyzed as compared to untreated controls. Notably, blastocysts from oocytes matured in cortisol-supplemented medium expressed higher relative levels of glucose transporter 1 (GLUT1), fatty acid synthase (FASN), and heat shock protein 70 (HSP70). This study supports a role for cortisol in the acquisition of bovine oocyte competence. This is evidenced by increased blastocyst development rates and presumably related to elevated embryonic transcripts with roles in glucose and lipid metabolism, as well as the cellular response to stress.

In vitro development of bison embryos using interspecies somatic cell nuclear transfer

Interspecies somatic cell nuclear transfer (interspecies SCNT) has been explored in many domestic and non-domestic animal species. However, problems arise during the development of these embryos, which may be related to species-specific differences in nuclear-cytoplasmic communication. The objectives of this study were to investigate the possibility of producing bison embryos in vitro using interspecies SCNT and assess the developmental potential of these embryos. Treatment groups consisted of cattle in vitro fertilization (IVF) and cattle SCNT as controls and wood bison SCNT, plains bison SCNT and wisent SCNT as experimental groups. Cleavage and blastocyst rates were assessed, and blastocyst quality was determined using total cell number, apoptotic incidence and relative quantification of mitochondria-related genes NRF1, MT-CYB and TFAM. These results indicate that embryos can be produced by interspecies SCNT in all bison species/subspecies (13.34-33.54% blastocyst rates). Although increased incidence of apoptosis was observed in bison SCNT blastocysts compared to cattle SCNT controls (10.45-12.69 vs 8.76, respectively) that corresponded with significantly lower cell numbers (80-87 cells vs >100 cells, respectively), no major differences were observed in the expression of NRF1, MT-CYB and TFAM. This study is the first to report the production of bison embryos by interspecies SCNT. Blastocyst development in all three bison species/subspecies was greater than the rates obtained in previous studies by IVF, which supports the potential role of SCNT for in vitro embryo production in this species. Yet, further investigation of developmental competence and the factors influencing blastocyst quality and viability is required.