The Laboratory of Molecular Genetics comprises groups headed by 10 independent investigators interested in genetic mechanisms of growth and differentiation in a variety of organisms. For some time, mechanisms of transcriptional control and intercellular communication have been a particular interest of the laboratory's researchers. Investigators devote considerable attention to the study of animal development, with research under way on Drosophila, Xenopus, and the zebrafish. The zebrafish has emerged as a particularly useful model system for the study of vertebrate development because of its small size, high fecundity, comparatively fast development, and its highly transparent embryo. These features allow embryological, molecular, and genetic tools to be applied effectively to this model system. First, we have generated a transgenic zebrafish line that specifically expresses green fluorescent protein in the vasculature from the beginning of its formation, allowing detailed in vivo analysis of blood vessel formation. Second, we have completed a gene expression screen in which we have evaluated over 2,700 cDNAs representing embryonic mRNAs, with 350 of the clones selected for further study because of their distinctive expression patterns. The cloned genes represent a valuable tool for various studies, some already completed and others in progress. A third major area of interest is the analysis of neural development in zebrafish by a combination of genetic, molecular, and imaging technologies. Studies have focused on the role of the Wnt and Notch signaling pathways in the patterning of the nervous system, a role that is clearly conserved throughout vertebrate development.