MUTATIONS AFFECTING CELL FATES AND CELLULAR REARRANGEMENTS DURING GASTRULATION IN ZEBRAFISH

One of the major challenges of developmental biology is understanding the inductive and morphogenetic processes that shape the vertebrate em bryo. In a large-scale genetic screen for zygotic effect, embryonic le thal mutations in zebrafish we have identified 25 mutations that affec t specification of cell fates and/or cellular rearrangements during ga strulation, These mutations define at least 14 complementation groups, four of which correspond to previously identified genes, Phenotypic a nalysis of the ten novel loci revealed three groups of mutations causi ng distinct effects on cell fates in the gastrula, One group comprises mutations that lead to deficiencies in dorsal mesodermal fates and af fect central nervous system patterning, Mutations from the second grou p affect formation of ventroposterior embryonic structures, We suggest that mutations in these two groups identify genes necessary for the f ormation, maintenance or function of the dorsal organizer and the vent ral signaling pathway, respectively, Mutations in the third group affe ct primarily cellular rearrangements during gastrulation and have comp lex effects on cell fates in the embryo, This group, and to some exten t mutations from the first two groups, affect the major morphogenetic processes, epiboly, convergence and extension, and tail morphogenesis. These mutations provide an approach to understanding the genetic cont rol of gastrulation in vertebrates.