Embryonic, fetal, and neonatal tongue myoblasts exhibit molecular heterogeneity in vitro

Variable gene expression patterns have been shown to exist between embryoni c, fetal, and neonatal lineages of limb skeletal myoblasts in vitro and in vivo. In this study, we examined the molecular phenotype of embryonic, feta l, and neonatal tongue myoblasts in primary culture for comparison with in vivo developmental tongue myoblasts. Myogenic regulatory factor (MRF) and m yosin heavy chain (MHC) gene expression were determined in culture during b oth growth and differentiation conditions by PCR, immunoblotting, and immun ohistochemistry. Unlike their in vivo tongue myoblast equivalents, developm ental tongue myoblast cultures featured the expression of MyoD when kept in growth conditions. Differentiation conditions in vitro induced myogenic to ngue lineages to maintain characteristics of their in vivo morphologic and contractile gene phenotype. Both in vivo and in vitro, embryonic tongue lin eages predominantly expressed MHC-embryonic isoforms, while fetal and neona tal tongue lineages predominantly expressed fast and perinatal isoforms of contractile genes. A notable difference from the in vivo condition that was observed in differentiated tongue myotubes in vitro was the presence of th e MHC-slow protein. It was previously demonstrated that MHC-slow protein wa s undetectable during the in vivo development of the tongue musculature des pite the abundance of slow isoform transcripts. The present characterizatio n of primary tongue myogenic cultures indicates that murine myoblast hetero geneity exists primarily between developmental lineages at the level of con tractile gene expression. Outside their native surroundings, developmental myogenic tongue populations are unable to recapitulate the determination an d differentiation molecular profiles that occur in vivo.