Effects of culture conditions and nuclear transfer protocols on blastocyst formation and mRNA expression in pre-implantation porcine embryos

Abstract

This study investigated the effects of culture conditions and somatic cell nuclear transfer (SCNT) protocols on in vitro development of porcine SCNT embryos and on expression patterns of genes involved in stress (heat shock protein 70.2, HSP70.2), trophoblastic function (integrin beta1, ITGB1), metabolism (phosphoglycerate kinase 1, PGK1), apoptosis (BAX), and imprinted gene (insulin-like growth factor 2 receptor, IGF2R). In Experiment 1, supplementing modified North Carolina State University (mNCSU) medium with 10% FBS at Day 4 of culture increased SCNT blastocyst formation (22.9 vs. 10.7%, P < 0.05), number of inner cell mass cells (13.3 ± 4.3 vs. 7.6 ± 2.2, P < 0.05), and total cells (57.9 ± 19.5 vs. 36.3 ± 8.2, P < 0.05) in cloned blastocysts. In Experiment 2, using culture medium with 10% FBS, 1.0 mM calcium in fusion/activation medium (1.0C), and 7.5 μg/mL cytochalasin B treatment (0.1C&CB) yielded higher rates (P < 0.05) of blastocysts (33.6 and 33.3%, respectively) relative to the control (0.1 mM calcium fusion medium, 0.1C; 18.3%). Total cell numbers of blastocysts were increased (P < 0.05) in 1.0C (77.4 ± 28.9) compared to the control (58.5 ± 22.6). In vitro-derived blastocysts had higher expression levels of BAX and lower levels of HSP70.2, IGF2R compared to their in vivo-derived counterparts. Supplementing culture medium with 10% FBS increased relative abundances of BAX mRNA in SCNT blastocysts relative to in vivo-derived blastocysts. The transcript level of ITGB1 in blastocyst from 0.1C&CB was lower than in vivo blastocysts. In conclusion, different culture conditions or SCNT protocols affected in vitro development of SCNT embryos and altered several important genes (BAX, HSP70.2, IGTB1, and IGF2R) compared to conventional in vivo-derived blastocysts.