Morphogenesis and evolution of vertebrate appendicular muscle

Area of Science:

• Evolutionary developmental biology
• Comparative embryology
• Vertebrate paleontology

Background:

• Appendicular muscle in fins and limbs is generated through two distinct vertebrate modes.
• Cartilaginous fishes (Chondricthyes) utilize a primitive muscle formation strategy.
• Amniotes (e.g., chick, mouse) and teleosts (e.g., zebrafish) share a more derived mechanism.

Purpose of the Study:

• To investigate the evolutionary origins of tetrapod limb muscle formation.
• To compare appendicular muscle development across different vertebrate lineages.
• To identify conserved genetic and developmental pathways.

Main Methods:

• Comparative analysis of muscle development in embryos of various vertebrate species.
• Gene expression analysis of fin and limb myoblasts.
• Embryological studies focusing on myotome interactions and cell migration.

Main Results:

• Cartilaginous fishes form fin muscles via direct epithelial myotomal extensions.
• Amniotes and teleosts develop limb/fin muscles from migratory mesenchymal myoblasts originating in somites.
• Migratory myoblasts in fins and limbs express conserved genes, indicating shared identity.

Conclusions:

• The mechanisms for tetrapod limb muscle formation predate the Sarcopterygian radiation.
• A conserved developmental program underlies appendicular muscle formation in diverse vertebrates.
• Understanding these mechanisms provides insight into vertebrate evolution.