The Emergence of Embryonic Myosin Heavy Chain during Branchiomeric Muscle Development

Abstract

A prerequisite for discovering the properties and therapeutic potential of branchiomeric muscles is an understanding of their fate determination, pattering and differentiation. Although the expression of differentiation markers such as myosin heavy chain (MyHC) during trunk myogenesis has been more intensively studied, little is known about its expression in the developing branchiomeric muscle anlagen. To shed light on this, we traced the onset of MyHC expression in the facial and neck muscle anlagen by using the whole-mount in situ hybridization between embryonic days E9.5 and E15.5 in the mouse. Unlike trunk muscle, the facial and neck muscle anlagen express MyHC at late stages. Within the branchiomeric muscles, our results showed variation in the emergence of MyHC expression. MyHC was first detected in the first arch-derived muscle anlagen, while its expression in the second arch-derived muscle and non-somitic neck muscle began at a later time point. Additionally, we show that non-ectomesenchymal neural crest invasion of the second branchial arch is delayed compared with that of the first brachial arch in chicken embryos. Thus, our findings reflect the timing underlying branchiomeric muscle differentiation.

New Insights into the Diversity of Branchiomeric Muscle Development: Genetic Programs and Differentiation

“…Previously, using double in situ hybridization analysis of whole mount chicken embryos, we reported that Sox10 and Ap2α expression can be used to analyze the respective location of neural crest cells in the pharyngeal arches [ 27 ]. More recently, we have revealed that non-ectomesenchymal neural crest cell invasion of the second pharyngeal arch is delayed compared with that of the first pharyngeal arch in chicken embryos ( Figure 4 B) [ 70 ]. We also observed HNK1-positive nerve fibers invading the mesodermal core of the pharyngeal arches ( Figure 3 E,F).…”

“…Therefore, an important open question in the field regards when MyHC expression emerges in branchiomeric muscle anlagen. We have recently addressed this question in mouse embryos by analyzing the onset of its expression in the branchiomeric muscles [ 70 ]. MyHC was first detected at embryonic day 10.5 ( Figure 5 A), and its peak expression occurred around embryonic day 13.5 ( Figure 5 D).…”