How does muscle tissue form in the limbs during embryonic development?

Muscle Formation in the Limbs During Embryonic Development

Muscle tissue in the limbs forms through the migration of muscle progenitor cells from the somitic myotome into the limb buds, where they proliferate and differentiate into skeletal muscle. 1, 2

Origin of Limb Muscle Progenitors

• Limb muscle progenitors originate specifically from the lateral portion of the dermomyotome, which is the epithelial dorsal part of the somite 1
• These progenitor cells undergo a critical process of de-epithelialization before migration, which is mediated by the interaction between SF/HGF and its receptor c-met 1
• During migration, these cells adopt a mesenchymal morphology while maintaining their myogenic specification through the expression of transcription factors including Pax3, Pax7, and myf5 1, 2

Migration Process

• After delamination from the lateral dermomyotome, muscle progenitor cells actively migrate into the developing limb bud 2
• This migration is regulated by specific signals from the lateral plate mesoderm 3
• During migration, premature differentiation is inhibited to allow for continued cell motility and proliferation 1
• The migrating cells maintain their myogenic identity without expressing differentiation markers 2

Muscle Formation in the Limb

• Upon reaching their target sites within the limb bud, the muscle progenitors coalesce to form dorsal and ventral myogenic zones 3
• Myogenesis is then initiated through the activation of muscle determination factors including MyoD, myogenin, and MRF4 1
• The progenitor cells proliferate and differentiate to form the complex pattern of limb muscles 3
• Interestingly, there appears to be a temporal pattern to migration, with early migrants giving rise predominantly to slow muscle fibers and later migrants forming fast muscle fibers 4

Regulation of Muscle Development

• The entire process from specification to differentiation is controlled by local signaling between embryonic structures 1
• Pax3 and its target c-met are essential for the delamination and migration of muscle progenitors 2
• Transcription factors Lbx1 and Mox2 play important roles in limb muscle development, with mutations revealing differences between forelimb and hindlimb muscle formation 2
• The myogenic regulatory factors (MRFs) including MyoD, Myf5, myogenin, and MRF4 are crucial for muscle cell determination and differentiation 2, 3

Clinical Implications

• Understanding the embryological development of limb muscles is important for comprehending congenital limb muscle abnormalities
• The process of muscle regeneration in adults recapitulates aspects of embryonic muscle development, with satellite cells (adult muscle stem cells) playing a role similar to embryonic muscle progenitors 1, 2
• Knowledge of normal muscle development provides insights into potential therapeutic approaches for muscle diseases and injuries

This developmental pathway explains why the correct answer to the original question is C: Muscle progenitors migrate from the somitic myotome and into the limb buds. The other options incorrectly identify the source of muscle progenitors or the migration process.