Development of single blastomeres derived from two-cell embryos produced in vitro in pigs

The objective was to investigate development of single blastomeres derived from IVP two-cell porcine embryos. There was no difference (P > 0.05) in blastocyst rates among intact two-cell embryos (IN), zona-free two-cell embryos (ZF), and single blastomere (SB) groups (50.0 ± 9.7, 57.4 ± 5.7, and 45.1 ± 7.2%, respectively; mean ± SEM). However, blastocyst yield for the SB group (90.2 ± 14.4%, based on the original number of two-cell embryos before blastomere separation) was higher (P < 0.05) than those of IN and ZF groups. Although the number of inner cell mass (ICM) and trophectoderm (TE) cells in SB blastocysts (6.2 ± 0.8 and 15.5 ± 1.1, respectively) was lower (P < 0.05) than those in IN (12.4 ± 1.3 and 26.0 ± 3.8) and ZF blastocysts (10.7 ± 1.6 and 26.4 ± 3.4), ICM:TE ratios did not differ significantly among groups. Expressions of transcripts associated with cellular organization (TUBA1 and TUBB) were reduced (P < 0.05) in SB versus IN blastocysts. However, there was no significant difference among groups for expression of transcripts associated with responses to stress (HSPE1, HSPD1, and HSPCA) or glucose catabolism (ENO1, COX6C, COX7B, NDUFA4, NDUFA13, UCRC, and UQCRFS1) in blastocysts. The percentage of the sister blastomere pairs in which both cells developed to blastocysts (36.6 ± 5.3%) or both degenerated (46.3 ± 10.3%) were higher (P < 0.05) than that of the pairs in which one developed to blastocyst while the other degenerated (17.1 ± 7.8%). When both pairs developed to blastocysts, one blastocyst had more (P < 0.05) ICM and TE cells (8.2 ± 1.2 and 20.2 ± 2.1, respectively) than the other (5.2 ± 0.9 and 13.5 ± 1.1), although ICM:TE cell ratios were not significantly different. In conclusion, blastomere separation at the two-cell stage significantly increased blastocyst yield from IVP porcine embryos. This might be a useful approach for conservation of rare pig breeds, in which low numbers of embryos limited the success of embryo transfer.