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Effect of the porcine IGF2 intron3 G3072A substitution on development and growth of skeletal muscle (1033.4)

A previously identified SNP that disrupts a binding site for a repressor, ZBED6, within intron 3 of the maternally imprinted IGF2 gene, (IGF2 G3072A) results in increased muscle but decreased fat accumulation in swine. Our objective was to determine how this mutation alters gene expression and muscle fiber types during prenatal and postnatal growth. Sows (AA) were bred to a heterozygous (AG) boar. For fetal samples, sows were euthanized at 60 and 90 days of gestation to obtain fetuses. Male and female pigs were also euthanized at birth (0d), weaning (21d), and at a market weight (175d). At 175d, muscle weights were increased approximately 5‐10% (P < 0.01) in pigs with paternal A compared to G alleles. As expected, IGF2 expression was increased 1.5 ‐ 4.5 fold (P < 0.05) in pigs possessing paternal A compared to G alleles at 0d, 21d and 175d. Unexpectedly, IGF2 expression tended to have a 1.5 fold increase (P < 0.10) in fetuses with paternal A compared to G alleles at 90 days of gestation. IGF2 was not different (P > 0.10) in fetuses at 60 days of gestation. At all time points, IGF1 expression was not affected (P > 0.10) by IGF2 allele. Myostatin, ZBED6, IGF1R, IGF2R, and Myosin Heavy Chains (1, 2a, 2x, 2b) expression were also not affected (P > 0.1) by IGF2 allele at 175d. These data suggest that increased IGF2, and not increased IGF1, is directly responsible for increased muscle weights observed in market weight animals.