248 Divergent Satellite Cell Profiles of Bovine Trapezius, Longissimus, and Bicep Femoris Muscles in Utero

Abstract

Abstract As we look to better understand whole body growth and development, there are still many mechanisms of individual muscle growth that we have yet to comprehend. Therefore, the objective of this study was to compare proliferative capacity and satellite cell number within the trapezius (TP), longissimus (LM), and bicep femoris (BF) muscles of fetal bovine throughout mid and late gestation. We hypothesized a difference in satellite cell number across these three muscles may further explain the differential growth pattern of each of these muscles in utero. Muscle samples were harvested from bovine fetuses at a commercial abattoir and aged using crown rump length (~150-220d in utero). These samples were then dissected into single fibers and seeded in a 3D hydrogel culture with 20% FBS media. Cells were fixed using 4% paraformaldehyde and stained for DAPI, Pax-7, Myf-5 (Invitrogen, Bedford, MA) at 72, 96, and 120h. Wells were imaged and analyzed for proliferation rate using the Cytation 5 (Agilent; La Jolla, CA) Prime Gen 5 software. Data were analyzed as a two-way ANOVA with repeated measures using GraphPad Prism (Version 9.5). For Myf-5, Pax-7, and dual positive cells (P ≤ 0.05) there was a difference across muscle type with BF having an increased number of positive cells compared with the TP muscle and LM being intermediate (Myf-5 mean = 51, 23, and 40 respectively; Pax-7 mean = 45, 30, and 20 respectively; Dual mean = 39, 20, 16 respectively). This variation was further supported by a similar divergence in proliferation rate across muscle type (P = 0.04), with BF muscle having increased proliferative capacity over TP muscle and LM muscle being intermediary. These findings suggest contrasting growth patterns across muscle types in utero that may influence postnatal growth patterns. Further research is needed to understand how the variability in satellite cell number contributes to differences in individual muscle growth.