CROTWELL, P.L.*; MABEE, P.M.; Univ. of South Dakota, Vermillion; Univ. of South Dakota, Vermillion: A comparative analysis of gene expression patterns conserved in segmentation of fish and tetrapod skeletons

Much skeletogenesis in zebrafish occurs at �late stages� for which there are few tools to test gene function. The study of mutants, for example, is limited because many of the important skeletogenic genes (e.g. shh, bmp2b, chordin) are so critical to early stages that mutants do not survive, with few exceptions, to the fin development stage. Those that do (e.g. a few chordin mutants) exhibit significant skeletal malformations (Fisher & Halpern, 1999). Morpholino technology has not been adapted for delivery to specific tissue at later stages. The standard chick and mouse technique of protein-soaked bead implantation has yielded no significant data in late stage zebrafish. Thus, though patterns of association of gene expression can be analyzed, and such data can be highly suggestive, definitive conclusions regarding the role of skeletogenic genes in older larvae must await the development of new functional and bioinformatic tools. We focused our study of the evolution of skeletal joints in vertebrates on the gene expression of 10 genes or gene pairs (including wnt9a and b, bmp2a and b, bmp4, gdf5, noggin, chordin, sox 9a and b, shh, bapx1, and collagen II) in the axial and appendicular skeleton of the zebrafish in relation to those patterns in tetrapod vertebrates. Overall similarity in expression patterns in conjunction with phylogenetic history and the fossil record suggests a pattern of inheritance and co-option in the deployment of these genes. We conclude that there is a unity in the mechanisms of skeletal development and patterning that has been conserved over 500 million years of vertebrate evolution.