256 LINES OF PIGS SELECTED FOR COMPONENT TRAITS OF LITTER SIZE EXHIBIT DIFFERENTIAL GENE REGULATION AT THE ONSET OF EMBRYO (TROPHECTODERM) ELONGATION

Abstract

Significant embryonic (<18%) loss occurs in the pig as the pre-implantation embryo undergoes a dramatic morphological change from ovoid (8-10 mm) at gestational Day 11 to a long, thin filament (<150 mm) by Day 12. Lines of pigs selected for increased uterine capacity have improved embryonic survival, whereas pigs selected for increased ovulation rate have decreased embryo survival. Alterations in the expression of genes that play key roles in embryo elongation and maternal recognition of pregnancy may reflect differences in embryo survival observed in these lines of pigs. The objective of the current study was to evaluate the expression level of transcripts involved in developmentally important processes, such as steroidogenesis, cellular differentiation, cell-cell interaction, and immune modulation, at the onset of porcine embryo elongation (gestational Day 11) in control animals and lines selected for increased ovulation rate or uterine capacity. Total RNA was isolated from Day 11 ovoid embryos, and gene expression was measured via real-time PCR. Data were analyzed for analysis of variance using GLM procedures. Expression of steroidogenic acute regulatory protein mRNA was decreased (P = 0.02) in embryos from the ovulation rate and uterine capacity lines compared with controls. Similarly, expression of cytochrome P450_scc and aromatase mRNA were decreased (P < 0.003) in embryos from the ovulation rate and uterine capacity lines, compared with the control line. Interestingly, 17±-hydroxylase mRNA expression was decreased (P = 0.0004) only in embryos from the ovulation rate line compared with the control and uterine capacity lines. In contrast, expression of cytokeratin-8 and -18 mRNA were increased (P < 0.02) in embryos from the uterine capacity and ovulation rate lines, compared with controls. Expression of galectin 1 mRNA was increased (P = 0.02) in embryos from the uterine capacity line, compared with the ovulation rate line. Expression of interleukin-1 receptor type 1 mRNA was increased (P = 0.03) in embryos from the uterine capacity line, compared with both the control and the uterine capacity lines. Constitutive expression of 17²-hydroxysteroid dehydrogenase, stratifin, and interleukin-1² mRNA were observed in embryos from all lines. These results demonstrate altered gene expression in embryos from pigs selected for increased uterine capacity and ovulation rate compared with controls, and may contribute to differences observed in embryo survival between these lines of pigs.