VINCENT, N. A. *; HALL, B. K.; Dalhousie University, Nova Scotia; Dalhousie University, Nova Scotia: Mechanisms of Development of the Neural Crest-Derived Skeleton in Hymenochirus boettgeri

A wealth of information has been collected regarding the mapping and development of the larval cartilaginous skeleton of anurans (frogs and toads). However, relatively little is known about the mapping of the adult bony skeleton, and even less about the mechanisms by which the cartilaginous larval skeleton is replaced by the bony skeleton during metamorphosis. Of particular interest is the development of the skull, which is largely derived from neural crest, a secondary germ layer arising from neural ectoderm during neurulation. To address the lack of information available on the mechanisms behind skull development, the current study utilized organ culture of presumptive mandibular (Meckel�s cartilage) mesenchyme, from various aged tadpoles, to determine the major control mechanisms of larval (cartilaginous) and adult (bony) mandibular development in the Dwarf African Clawed Frog, Hymenochirus boettgeri. Some cultures were supplemented with either exogenous thyroxine or thiourea (a thyroxine inhibitor). These cultures are being used to assess (1) whether an epithelial-mesenchymal interaction is involved in the initiation of skeletogenesis; (2) whether thyroxine, a hormone essential to the mid-ontogenetic transformations of metamorphosing amphibians, plays a role in skeletogenesis, specifically by mediating the disappearance of Meckel�s cartilage and subsequent development of the bony mandible in its place; (3) whether skeletogenesis involves a combination of 1 and 2. Preliminary results discuss stage specificity, survival, growth and differentiation of the cultures. This approach should provide important information regarding the mechanisms by which both the larval cartilaginous and the adult bony skeletons develop in anurans.