The proposed research represents a collaborative research project entitled "Embryonic Stem Cell Equivalents in Zebrafish to Study Early Development". The three principle investigators are Nancy Hopkins (Massachusetts Institute of Technology), Wilbur Long (Western Maryland College), and Paul Collodi (Purdue). The long range goal is to understand early developmental processes at the genetic level in the zebrafish, Brachydanio rerio. The immediate goal is to follow up promising new results which suggest that it may be possible to develop an equivalent to mouse embryonic stem (ES) cells for zebrafish. With this technology, one can mutate genes by random insertion of promoter or gene trap constructs or by targeted homologous recombination, select cells with desired alterations, and then generate mutant organisms from them. The zebrafish would be a superb organism in which to perform this type of mutagenesis and if successful, this approach would make it possible to isolate large numbers of insertional mutants affecting the desired developmental processes as well as targeted mutations in genes suspected of playing important roles in the processes.