“Soft” tissue patterning: Muscles and tendons of the limb take their form

Abstract

The musculoskeletal system grants our bodies a vast range of movements. Because it is mainly composed of easily identifiable components, it serves as an ideal model to study patterning of the specific tissues that make up the organ. Surprisingly, although critical for the function of the musculoskeletal system, understanding of the embryonic processes that regulate muscle and tendon patterning is very limited. The recent identification of specific markers and the reagents stemming from them has revealed some of the molecular events regulating patterning of these soft tissues. This review will focus on some of the current work, with an emphasis on the roles of the muscle connective tissue, and discuss several key points that addressing them will advance our understanding of these patterning events.

The developmental basis of bat wing muscle

“…In vertebrates, skeletal muscles which form in the head, trunk and limbs are patterned by extrinsic cues from surrounding tissues to adopt specific arrangements of muscle fibres in the adult form [23][24][25][26][27][28][29][30][31] . For example, somite-derived limb muscle precursor cells migrate into the limb bud which is filled with lateral platederived connective tissue.…”

“…Although molecular mechanisms controlling the organization of skeletal muscle in space during vertebrate development are not fully understood, signalling molecules secreted from non-myogenic mesenchyme or muscle connective tissue, as well as cell adhesion molecules localized at the cell membrane of muscle connective tissue, potentially affect the architectural pattern of muscles 21,22,30,[40][41][42][43][44][45][46][47][48] . In tongue morphogenesis, cranial neural crest-derived tongue muscle connective tissue is required for organizing occipital somite-derived tongue muscle cells 49 .…”

Muscle composition is regulated by a Lox-TGFβ feedback loop

“…Disruption of MCT integrity, organization or composition affects myogenic progenitor specification, differentiation, patterning, morphogenesis and regeneration (Grim and Wachtler, 1991;Kardon et al, 2003;Hasson et al, 2010;Mathew et al, 2011;, demonstrating that crosstalk between these muscle components plays a cardinal role during myogenesis. However, the molecular signals involved and the ECM molecules carrying out these activities have remained largely unknown (Hasson, 2011).…”

Axial and limb muscle development: dialogue with the neighbourhood

“…Moreover, transcription factor TCF4 specific to fibroblasts is necessary for slow myosin heavy chain expression, and, therefore, for the specification of muscle fibre type, as well as for the maturation of foetal muscles into adult muscles [119]. The role of muscle connective tissues was also observed from the deletion of the transcription factors Tbx5 and Tbx4 specific to connective tissues in the mouse forelimb and hindlimb, respectively [120,121]. In these mutant embryos, the morphogenesis of both muscles and tendons is affected [120], showing again the importance of the connective tissue for the development of associated muscles.…”