THE IDENTIFICATION OF GENES WITH UNIQUE AND ESSENTIAL FUNCTIONS IN THE DEVELOPMENT OF THE ZEBRAFISH, DANIO-RERIO

In a large-scale screen, we isolated mutants displaying a specific vis ible phenotype in embryos or early larvae of the zebrafish, Danio reri o. Males were mutagenized with ethylnitrosourea (ENU) and F-2 families of single pair matings between sibling F-l fish, heterozygous for a m utagenized genome, were raised. Egg lays were obtained from several cr osses between F-2 siblings, resulting in scoring of 3857 mutagenized g enomes. F-3 progeny were scored at the second, third and sixth day of development, using a stereomicroscope. In a subsequent screen, fixed e mbryos were analyzed for correct retinotectal projection. A total of 4 264 mutants were identified. Two thirds of the mutants displaying rath er general abnormalities were eventually discarded. We kept and charac terized 1163 mutants. In complementation crosses performed between mut ants with similar phenotypes, 894 mutants have been assigned to 372 ge nes. The average allele frequency is 2.4. We identified genes involved in early development, notochord, brain, spinal cord, somites, muscles , heart, circulation, blood, skin, fin, eye, otic vesicle, jaw and bra nchial arches, pigment pattern, pigment formation, gut, liver, motilit y and touch response. Our collection contains alleles of almost all pr eviously described zebrafish mutants. From the allele frequencies and other considerations we estimate that the 372 genes defined by the mut ants probably represent more than half of all genes that could have be en discovered using the criteria of our screen. Here we give an overvi ew of the spectrum of mutant phenotypes obtained, and discuss the limi ts and the potentials of a genetic saturation screen in the zebrafish.