MYOSIN HEAVY-CHAIN GENE-EXPRESSION IN BOVINE FETUSES AND NEONATES REPRESENTING GENOTYPES WITH CONTRASTING PATTERNS OF GROWTH

Fetal and neonatal myosin heavy chain (MHC) gene expression was examin ed in bovine genotypes that differed in their postnatal growth pattern and mature size. Pregnancies were established that would be expected to produce early-, intermediate-, or late-maturing postnatal growth. F etal skeletal and cardiac muscles were collected at 100 and 200 days o f gestation and at 30 days of age. Muscle tissue was analyzed for rela tive levels of MHC RNA and protein. Longissimus muscle MHC RNA/mu g RN A was greater at the 100-day time point for the intermediate maturity type (P < 0.05), which differed from the 200-day time point where the early maturity type had the greater RNA level (P < 0.05). Triceps musc le MHC RNA/mu g RNA weights differed due to genotype at 200 days gesta tion but did not differ at 100 days gestation or at 30 days postnatal. Ventricular muscle MHC RNA did not differ due to genotype at any of t he three developmental stages. Differences due to maturity type in MHC protein/mg DNA were observed at 30 days of age, but no differences du e to maturity type were observed at the prenatal time points. These re sults indicate that bovine fetal skeletal muscle MHC RNA production ca n be influenced by genotype and that genotype may be an important fact or for future studies examining the role of external influences on fet al muscle growth.