Sexual maturity and reproductive phase of oocyte donor influence the developmental ability and apoptosis of cloned and parthenogenetic porcine embryos

This study investigated the influence of the sexual maturity and reproductive phase of oocyte donor on the developmental ability and quality of porcine embryos produced by somatic cell nuclear transfer (SCNT) or parthenogenesis (PA). Blastocyst quality was evaluated in terms of hatching ability, total nuclei number and types of apoptosis. Results revealed that maturation rate was not influenced by the reproductive status of the oocyte donor. However, when subjected to PA or SCNT, embryos derived from sexually mature sow oocytes developed to blastocysts at higher rates and had higher cell number than those derived from immature gilt oocytes (p < 0.05). Significant effect of reproductive phase, luteal versus follicular, was also noted with luteal stage oocytes yielding higher (p < 0.05) rate of blastocyst formation (PA: 54.3 ± 1.3% versus 44.8 ± 0.3%; SCNT: 29.4 ± 0.2% versus 22.7 ± 0.1%). Blastocysts derived from luteal phase oocytes also had higher (p < 0.05) hatching ability (PA: 44.2 ± 1.1%; SCNT: 39.6 ± 4.7%) and cell number (PA: 77.4 ± 4.9; SCNT: 54.9 ± 2.4) than those derived from follicular phase oocytes (PA: 34.9 ± 0.9%, 67.2 ± 3.9; SCNT: 34.6 ± 2.7%, 47.5 ± 2.9). TUNEL assay and Hoechst 33342 staining revealed that percentage of blastocysts showing total apoptosis did not differ among the groups. However, luteal phase oocyte-derived blastocysts had the highest incidence of nuclear fragmentation. Among cloned blastocysts that showed the signs of apoptosis, the highest index of total apoptosis was observed in prepubertal oocyte-derived blastocysts (5.2 ± 0.7). Blastocysts derived from luteal phase oocytes showed the lowest TUNEL index (2.0 ± 0.5). The present study therefore, indicates that the sexual maturity and reproductive phase of cytoplast donor significantly influences the developmental ability, apoptosis and quality of blastocysts produced by SCNT or PA. Oocytes from sexually mature sows in luteal phase of their reproductive cycle may be better cytoplast recipients for SCNT.