224 Awardee Talk: Investigating Muscle Fiber Hypertrophy During pre- and Post-Natal Growth

Abstract

Abstract Research has established that muscle fiber hyperplasia is complete during mid gestation; therefore, skeletal muscle fiber hypertrophy is responsible for the increase in muscle mass observed during late gestation and postnatal growth periods. Our research is investigating key times points during muscle fiber hypertrophy and the role of miRNA and mRNA transcriptome in this process. Two studies were conducted to examine changes in muscle mass, muscle fiber hypertrophy, and gene expression from gestational d (gd) 85 to market weight in Suffolk or Texel cross lambs. Longissimus muscle (LM) samples were taken for muscle fiber histology at the following time points: gd85, gd110, gd133, and market (d243) in study one and at postnatal d2, d14 and d203 in study two. microRNA (miRNA) and mRNA sequencing of the LM were conducted in study one and included biopsies at d 42 and 65. Type I and Type II muscle fiber area increased (P < 0.05) at each stage of growth evaluated. Type I muscle fiber area increased by 26.7-fold and Type II muscle fiber area increased by 37.4-fold from gd85 to market (d243). mRNA sequencing identified a total of 9360 unique genes differentially expressed (DEGs; P < 0.05) in LM during hypertrophic growth but the majority of DEGs were observed in the prenatal (51%) and early postnatal (54%) periods. There were 142 unique miRNAs differentially expressed (P < 0.05) during hypertrophic growth of LM but the majority (62%) were observed in the transition period from prenatal to postnatal growth. Overall, muscle fiber hypertrophy is dynamic from late gestation through postnatal growth, but transcriptomic changes indicate key time periods during development in which mechanisms underlying hypertrophic growth may be altered.