Evolution and development of skeletal musculature in early vertebrates: insights from lamprey and shark embryos

Evolution and development of skeletal musculature in early vertebrates: insights from lamprey and shark embryos

Speaker: Professor Rie Kusakabe, Laboratory for Evolutionary Morphology, RIKEN Center for Biosystems Dynamics Research (BDR), Japan

Host: Simon Hughes

Abstract: 

During vertebrate embryogenesis, somites give rise to a wide variety of complex and functionally specialized muscles, such as muscles in the paired appendages, shoulder girdles, diaphragm and the tongue. Precursors of each muscle undergo migration/extension toward the site of differentiation where they form mature myofilaments at remarkably varied timings. In order to clarify the evolutionary mechanisms underlying the formation of complex muscles, we have examined the expression of developmental genes and protein markers in the jawless cyclostome lampreys, the shark, and other gnathostome species. During embryogenesis of the lamprey, which lacks paired fins, precursors forming coherent hypobranchial muscles emerge from the ventral edges of the anterior somites, stay lateral to the pharynx, and differentiate much later than other somitic muscles. On the other hand, sharks possess paired fins and compartmentalized hypobranchial muscles with its anterior part fused in the midline, similarly to other gnathostomes. Comparison of the tissue structure and the expression of developmental genes have illustrated the differential regulation of fin and hypobranchial muscles in each species. Our analyses provide new insights for cellular and molecular characteristics of the tongue and other musculatures as well as for their contribution to the complexity of the vertebrate body plan.