CROTWELL, P.L.*; MABEE, P.M.; Univ. South Dakota, Vermillion; Univ. South Dakota, Vermillion: Joints, co-option, and functional approaches in late-stage zebrafish

Significant evolutionary changes in morphology are frequently manifested late in development. What is considered �late� in molecular developmental biology is defined in part by molecular genetic tools available to test gene function. Zebrafish researchers who study development up to ~5 days post-fertilization (dpf) have available to them several standard tools, including morpholinos, cell lineage tracing, and mutants. In contrast, those of us who study events that occur later in development (8-28 dpf), such as skeletal morphogenesis, have been significantly challenged by lack of functional tools. Several of the genes we hypothesize to be involved in fin radial development and segmentation (e.g. Wnt14, Gdf5, noggin) are so critical to early stages that mutants do not survive to the fin development stage. Morpholino technology has not been adapted for delivery to specific tissue at later stages, including those we study. Our approach has thus far been limited to comparative expression data to investigate our hypothesis that the mechanisms underlying radial segmentation in fishes have been co-opted over several million years of evolution to give rise to tetrapod synovial joints. We recently have begun using a pharmacological approach to test the functional interactions of several target genes. We present here comparative expression data for radial vs. joint development, and show effects of cyclopamine on radial development in zebrafish larvae 8-28 dpf.