Origin of evolutionay novelties in turtles by developmental repatterning Shigeru Kuratani Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB) The turtle carapace, or the dorsal moiety of the shell, is derived from the rib, and is often regarded to represent a typical evolutionary novelty for its reversed topographical relationship with the pectoral girdle that is situated within the shell, unlike in other amniotes. To reveal the developmental factors behind this anatomical discrepancy, comparative molecular analyses of Pelodiscus sinensis embryos were carried out. During P. sinensis development, basic topographic relationships between muscle- and skeletal anlagen were largely conserved among amniotes, but some muscles that initially arose in the limb bud acquired novel insertion unique to the turtles. Thus the turtle body plan appears to be based upon novel direction of folding as well as invention of new connectivity. Along the line of turtle-specific folding arises the turtle-specific embryonic structure called the carapacial ridge (CR), which has been suspected to induce the turtle-specific rib growth pattern. To explore the mechanical background for this folding, we isolated CRABP-1, Sp-5, Lef-1, and APCDD1 as CR-specific genes. These genes were not P. sinensis-specific, but the evolutionary changes were introduced to ther regulation uniquley in the lineage of turtles. Inactivation of Lef-1 function or surgical removal of CR lead to the partial arrest of marginal growth of the carapace, suggesting that this structure is primarily for the carapacial growth, not for the rib patterning.

Origin of evolutionay novelties in turtles by developmental repatterning

Shigeru Kuratani

Laboratory for Evolutionary Morphology, RIKEN Center for Developmental Biology (CDB)

The turtle carapace, or the dorsal moiety of the shell, is derived from the rib, and is often regarded to represent a typical evolutionary novelty for its reversed topographical relationship with the pectoral girdle that is situated within the shell, unlike in other amniotes. To reveal the developmental factors behind this anatomical discrepancy, comparative molecular analyses of Pelodiscus sinensis embryos were carried out. During P. sinensis development, basic topographic relationships between muscle- and skeletal anlagen were largely conserved among amniotes, but some muscles that initially arose in the limb bud acquired novel insertion unique to the turtles. Thus the turtle body plan appears to be based upon novel direction of folding as well as invention of new connectivity. Along the line of turtle-specific folding arises the turtle-specific embryonic structure called the carapacial ridge (CR), which has been suspected to induce the turtle-specific rib growth pattern. To explore the mechanical background for this folding, we isolated CRABP-1, Sp-5, Lef-1, and APCDD1 as CR-specific genes. These genes were not P. sinensis-specific, but the evolutionary changes were introduced to ther regulation uniquley in the lineage of turtles. Inactivation of Lef-1 function or surgical removal of CR lead to the partial arrest of marginal growth of the carapace, suggesting that this structure is primarily for the carapacial growth, not for the rib patterning.