Signaling across the head trunk interface licences expansion of a muscle originating in pharyngeal mesoderm into the trunk territory. Muscle primordia labelled by expression of the myogenic regulatory gene MyoD at embryonic day 12.5 in a control embryo (left) versus an embryo in which retinoid signal reception is blocked in somitic mesoderm (right). Note the specific loss of the trapezius muscle primordium (arrow) in the embryo on the right, while craniofacial (CF), forelimb (FL) and trunk (T) primordia develop normally.

Skeletal muscles of the head and trunk originate in pharyngeal and somitic mesoderm respectively and develop through distinct upstream regulatory pathways. Dissecting the heterogeneity of myogenic programs is essential to understanding the origins of myopathies that often affect particular muscle groups.

Camille Dumas and colleagues in the Kelly lab have defined a unique genetic program controlling morphogenesis of the trapezius neck muscle at the head/trunk interface. This muscle originates in the head and expands into the trunk region to coordinate movements of the head, spine and scapula.  The trapezius evolved with the vertebrate neck to facilitate predation and is affected in certain genetic syndromes.

In the work published in Development Dumas et al used genetic and pharmacological approaches to reveal that retinoid signalling to somitic mesoderm is essential to licence expansion of the trapezius primordium into the trunk territory. Future work will define the retinoid-dependent downstream signals that signal to pharyngeal mesoderm to control trapezius development.

Dumas CE, Rousset C, De Bono C, Cortés C, Jullian E, Lescroart F, Zaffran S, Adachi N, Kelly RG. Retinoic acid signalling regulates branchiomeric neck muscle development at the head/trunk interface. Development. 2024 Aug 15;151(16):dev202905. doi: 10.1242/dev.202905. Epub 2024 Aug 29. PMID: 39082789.