Cxcr4 and Sdf-1 are critically involved in the formation of facial and non-somitic neck muscles

The development of thoracic and abdominal muscle depends on SDF1 and CXCR4

In vertebrates, the lateral body wall muscle formation is thought to be initiated by direct outgrowth of the dermomyotomes resulting in the elongation of the hypaxial myotomes. This contrasts with the formation of the muscles of the girdle, limbs and intrinsic tongue muscles, which originate from long-range migrating progenitors. Previous work shows that the migration of these progenitors requires CXCR4 which is specifically expressed in the migrating cells, but not in the dermomyotome. Here, we show that cells in the ventrolateral-lip (VLL) of the dermomyotome at the flank level express CXCR4 in a pattern consistent with that of Pax3 and MyoR. In ovo gain-of-function experiments using electroporation of SDF-1 constructs into the VLL resulted in increased expression of c-Met, Pax3 and MyoD. In contrast, a loss-of-function approach by implantation of CXCR4-inhibitor beads into the VLL of the flank region caused a reduction in the expression of these markers. These data show that CXCR4 is expressed in the VLL, and by experimentally manipulating the CXCR4/SDF-1 signaling, we demonstrate the importance of this axis in body wall muscle development.

Chicken embryo as a model in second heart field development

Previously, a single source of progenitor cells was thought to be responsible for the formation of the cardiac muscle. However, the second heart field has recently been identified as an additional source of myocardial progenitor cells. The chicken embryo, which develops in the egg, outside the mother can easily be manipulated in vivo and in vitro. Hence, it was an excellent model for establishing the concept of the second heart field. Here, our review will focus on the chicken model, specifically its role in understanding the second heart field. In addition to discussing historical aspects, we provide an overview of recent findings that have helped to define the chicken second heart field progenitor cells. A better understanding of the second heart field development will provide important insights into the congenital malformations affecting cardiac muscle formation and function.

The chemokine receptor CXCR4 regulates satellite cell activation, early expansion, and self-renewal, in response to skeletal muscle injury

Acute skeletal muscle injury is followed by satellite cell activation, proliferation, and differentiation to replace damaged fibers with newly regenerated muscle fibers, processes that involve satellite cell interactions with various niche signals. Here we show that satellite cell specific deletion of the chemokine receptor CXCR4, followed by suppression of recombination escapers, leads to defects in regeneration and satellite cell pool repopulation in both the transplantation and in situ injury contexts. Mechanistically, we show that endothelial cells and FAPs express the gene for the ligand, SDF1α, and that CXCR4 is principally required for proper activation and for transit through the first cell division, and to a lesser extent the later cell divisions. In the absence of CXCR4, gene expression in quiescent satellite cells is not severely disrupted, but in activated satellite cells a subset of genes normally induced by activation fail to upregulate normally. These data demonstrate that CXCR4 signaling is essential to normal early activation, proliferation, and self-renewal of satellite cells.

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

Simple Summary

We review the transcription factors and signaling molecules driving differentiation of a subset of head muscles known as the branchiomeric muscles due to their origin in the pharyngeal arches. We provide novel data on the distinct myogenic programs within these muscles and explore how the cranial neural crest cell regulates branchiomeric muscle patterning and differentiation.

Abstract

Branchiomeric skeletal muscles are a subset of head muscles originating from skeletal muscle progenitor cells in the mesodermal core of pharyngeal arches. These muscles are involved in facial expression, mastication, and function of the larynx and pharynx. Branchiomeric muscles have been the focus of many studies over the years due to their distinct developmental programs and common origin with the heart muscle. A prerequisite for investigating these muscles’ properties and therapeutic potential is understanding their genetic program and differentiation. In contrast to our understanding of how branchiomeric muscles are formed, less is known about their differentiation. This review focuses on the differentiation of branchiomeric muscles in mouse embryos. Furthermore, the relationship between branchiomeric muscle progenitor and neural crest cells in the pharyngeal arches of chicken embryos is also discussed. Additionally, we summarize recent studies into the genetic networks that distinguish between first arch-derived muscles and other pharyngeal arch muscles.

Classification of early age facial growth pattern and identification of the genetic basis in two Korean populations

Childhood to adolescence is an accelerated growth period, and genetic features can influence differences of individual growth patterns. In this study, we examined the genetic basis of early age facial growth (EAFG) patterns. Facial shape phenotypes were defined using facial landmark distances, identifying five growth patterns: continued-decrease, decrease-to-increase, constant, increase-to-decrease, and continued-increase. We conducted genome-wide association studies (GWAS) for 10 horizontal and 11 vertical phenotypes. The most significant association for horizontal phenotypes was rs610831 (TRIM29; β = 0.92, p-value = 1.9 × 10⁻⁹) and for vertical phenotypes was rs6898746 (ZSWIM6; β = 0.1103, p-value = 2.5 × 10⁻⁸). It is highly correlated with genes already reported for facial growth. This study is the first to classify and characterize facial growth patterns and related genetic polymorphisms.

The Emergence of Embryonic Myosin Heavy Chain during Branchiomeric Muscle Development

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.

Diversity in cranial muscles: Origins and developmental programs

Cranial muscles have been the focus of many studies over the years because of their unique developmental programs and relative resistance to illnesses. In addition, head muscles possess clonal relationships with heart muscles and have been highly remodeled during vertebrate evolution. Here, we provide an overview of recent findings that have helped to redefine the boundaries and lineages of cranial mesoderm. These studies have important implications regarding the emergence of muscle connective tissues, which can share a common origin with skeletal muscle. We also highlight new regulatory networks of various muscle subgroups, particularly those derived from the most caudal arches, which remain poorly defined. Finally, we suggest future research avenues to characterize the nature of their intrinsic specificities and their emergence during evolution.

Chicken Second Branchial Arch Progenitor Cells Contribute to Heart Musculature in vitro and in vivo

In the past, the heart muscle was thought to originate from a single source of myocardial progenitor cells. More recently, however, an additional source of myocardial progenitors has been revealed to be the second heart field, and chicken embryos were important for establishing this concept. However, there have been few studies in chicken on how this field contributes to heart muscles in vitro. We have developed an ex vivo experimental system from chicken embryos between stages HH17-20 to investigate how mesodermal progenitors in the second branchial arch (BA2) differentiate into cardiac muscles. Using this method, we presented evidence that the progenitor cells within the BA2 arch differentiated into beating cardiomyocytes in vitro. The beating explant cells were positive for cardiac actin, Nkx2.5, and ventricular myosin heavy chain. In addition, we performed a time course for the expression of second heart field markers (Isl1 and Nkx2.5) in the BA2 from stage HH16 to stage HH21 using in situ hybridization. Accordingly, using EGFP-based cell labeling techniques and quail-chicken cell injection, we demonstrated that mesodermal cells from the BA2 contributed to the outflow tract and ventricular myocardium in vivo. Thus, our findings highlight the cardiogenic potential of chicken BA2 mesodermal cells in vitro and in vivo.

The CXCR4/SDF-1 Axis in the Development of Facial Expression and Non-somitic Neck Muscles

Trunk and head muscles originate from distinct embryonic regions: while the trunk muscles derive from the paraxial mesoderm that becomes segmented into somites, the majority of head muscles develops from the unsegmented cranial paraxial mesoderm. Differences in the molecular control of trunk versus head and neck muscles have been discovered about 25 years ago; interestingly, differences in satellite cell subpopulations were also described more recently. Specifically, the satellite cells of the facial expression muscles share properties with heart muscle. In adult vertebrates, neck muscles span the transition zone between head and trunk. Mastication and facial expression muscles derive from the mesodermal progenitor cells that are located in the first and second branchial arches, respectively. The cucullaris muscle (non-somitic neck muscle) originates from the posterior-most branchial arches. Like other subclasses within the chemokines and chemokine receptors, CXCR4 and SDF-1 play essential roles in the migration of cells within a number of various tissues during development. CXCR4 as receptor together with its ligand SDF-1 have mainly been described to regulate the migration of the trunk muscle progenitor cells. This review first underlines our recent understanding of the development of the facial expression (second arch-derived) muscles, focusing on new insights into the migration event and how this embryonic process is different from the development of mastication (first arch-derived) muscles. Other muscles associated with the head, such as non-somitic neck muscles derived from muscle progenitor cells located in the posterior branchial arches, are also in the focus of this review. Implications on human muscle dystrophies affecting the muscles of face and neck are also discussed.