Transforming growth factor alpha up-regulates desmin expression during embryonic mouse tongue myogenesis.

Myogenesis is determined by a set of myogenic differentiation factors that are, in turn, regulated by a number of peptide growth factors. During embryonic mouse tongue formation, transforming growth factor alpha (TGF alpha), epidermal growth factor (EGF), and their cognate receptor (EGFR) are co-expressed spatially and temporally with desmin, a muscle-specific structural protein. This investigation tested the hypothesis that TGF alpha directly regulates the myogenic program in developing tongue myoblasts. Mandibular processes from the first branchial arch of embryonic day 10.5 (E10.5) mouse embryos were microdissected and explanted into an organ culture system using serumless chemically defined medium. Exogenous TGF alpha at 10 and 20 ng/ml specifically increased the amount of desmin expression and the number of desmin-positive cells without affecting the general growth and development of the mandibles. This inductive response was detected as early as 2 days after treatment and sustained up to 9 days in culture. EGFR antisense oligonucleotides (30 microM) as well as tyrphostin (80 microM) were able to negate TGF alpha-induced up-regulation of desmin expression. These data indicate that autocrine and/or paracrine action of TGF alpha promotes tongue myogenesis, and that this action is mediated through functional kinase activity of the EGFR. We speculate that the myogenic program in the developing mouse tongue is dependent upon growth factor mediated cell-cell communication of mesenchymal cells originating from the occipital somites and ectomesenchymal cells originating from the cranial neural crest.