Tbx4 and Tbx5 Acting in Connective Tissue Are Required for Limb Muscle and Tendon Patterning

Abstract

Summary Proper functioning of the musculo-skeletal system requires the precise integration of bones, muscles and tendons. Complex morphogenetic events ensure that these elements are linked together in the appropriate 3D configuration. It has been difficult, however, to tease apart the mechanisms that regulate tissue morphogenesis. We find that deletion of Tbx5 in forelimb (or Tbx4 in hindlimbs) specifically affects muscle and tendon patterning without disrupting skeletal development thus suggesting that distinct cues regulate these processes. We identify muscle connective tissue as the site of action of these transcription factors and show that N-Cadherin and β-Catenin are key downstream effectors acting in muscle connective tissue regulating soft-tissue morphogenesis. In humans, TBX5 mutations lead to Holt-Oram syndrome, which is characterised by forelimb musculo-skeletal defects. Our results suggest that a focus on connective tissue is required to understand the aetiology of diseases affecting soft tissue formation.

The developmental basis of bat wing muscle

“…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 .…”

Molecular profiling of synovial joints: Use of microarray analysis to identify factors that direct the development of the knee and elbow

“…4B). The hindlimb-specific genes Tbx4 (Minguillon et al, 2005;Hasson et al, 2010), and Hoxc10 (Peterson et al, 1994;Nelson et al, 1996) were then examined. Tbx4 was detected in proliferating, prehypertrophic, and hypertrophic chondrocytes of the femur Developmental Dynamics Functional classification (GO Term) P value Multicellular organismal process 2.22*10-7 Transcription factor activity 7.40*10-7 Skeletal system development 9.85*10-7…”

Regulation of limb bud initiation and limb‐type morphology

“…1C). During a brief second phase, when the limb bud can develop autonomously, deletion of Tbx5 in forelimbs or Tbx4 in hindlimbs has no effect on outgrowth of the limb skeleton but rather specifically affects muscle and tendon morphogenesis (Hasson et al, 2010). It is likely that Tbx5 and Tbx4 proteins have distinct targets during these two phases of activity.…”

“…Transplants of wing bud mesenchyme combined with leg bud ectoderm transplanted to the flank will develop into wing structures, while reciprocal grafts of leg mesenchyme covered with wing ectoderm produce leg elements (Zwilling, 1959;Logan, 2003;Saunders and Gasseling, 1968). Both classical embryology and more recent molecular data indicate that limb muscles are patterned by extrinsic cues (Hasson et al, 2010;Christ et al, 1977;Kardon et al, 2003). Muscle progenitors that migrate into a forelimb bud develop into forelimb muscles in response to environmental signals present in the forelimb and hindlimb muscle progenitors respond to equivalent cues in the hindlimb environment.…”