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Imadeldin Yahya, Marion Böing, Qin Pu, Malte Puchert, Veysel Oedemis, Jürgen Engele, Beate Brand-Saberi, Gabriela Morosan-Puopolo

• The present study shows that the \(\it CXCR4/SDF-1\) axis regulates the migration of second branchial arch-derived muscles as well as non-somitic neck muscles. \(\it Cxcr4\) is expressed by skeletal muscle progenitor cells in the second branchial arch (BA2). Muscles derived from the second branchial arch, but not from the first, fail to form in \(\it Cxcr4\) mutants at embryonic days E13.5 and E14.5. \(\it Cxcr4\) is also required for the development of non-somitic neck muscles. In \(\it Cxcr4\) mutants, non-somitic neck muscle development is severely perturbed. In vivo experiments in chicken by means of loss-of-function approach based on the application of beads loaded with the CXCR4 inhibitor AMD3100 into the cranial paraxial mesoderm resulted in decreased expression of \(\it Tbx1\) in the \(\it BA2\). Furthermore, disrupting this chemokine signal at a later stage by implanting these beads into the \(\it BA2\) caused a reduction in \(\it MyoR\), \(\it Myf5\) and \(\it MyoD\) expression. In contrast, gain-of-function experiments based on the implantation of \(\it SDF-1\) beads into \(\it BA2\) resulted in an attraction of myogenic progenitor cells, which was reflected in an expansion of the expression domain of these myogenic markers towards the \(\it SDF-1\) source. Thus, \(\it Cxcr4\) is required for the formation of the \(\it BA2\) derived muscles and non-somitic neck muscles.