A GENETIC SCREEN FOR MUTATIONS AFFECTING EMBRYOGENESIS IN ZEBRAFISH

Systematic genome-wide mutagenesis screens for embryonic phenotypes ha ve been instrumental in the understanding of invertebrate and plant de velopment, Here, we report the results from the first application of s uch a large-scale genetic screening to vertebrate development. Male ze brafish were mutagenized with N-ethyl N-nitrosourea to induce mutation s in spermatogonial cells at an average specific locus rate of one in 651 mutagenized genomes, Mutations were transmitted to the F-1 generat ion, and 2205 F-2 families were raised. F-3 embryos from sibling cross es within the F-2 families were screened for developmental abnormaliti es, A total of 2337 mutagenized genomes were analyzed, and 2383 mutati ons resulting in abnormal embryonic and early larval phenotypes were i dentified. The phenotypes of 695 mutants indicated involvement of the identified loci in specific aspects of embryogenesis. These mutations were maintained for further characterization and were classified into categories according to their phenotypes, The analyses and genetic com plementation of mutations from several categories are reported in sepa rate manuscripts, Mutations affecting pigmentation, motility, muscle a nd body shape have not been extensively analyzed and are listed here, A total of 331 mutations were tested for allelism within their respect ive categories, This defined 220 genetic loci with on average 1.5 alle les per locus. For about two-thirds of all loci only one allele was is olated, Therefore it is not possible to give a reliable estimate on th e degree of saturation reached in our screen; however, the number of g enes that can mutate to visible embryonic and early larval phenotypes in zebrafish is expected to be several-fold larger than the one for wh ich we have observed mutant alleles during the screen. This screen dem onstrates that mutations affecting a variety of developmental processe s can be efficiently recovered from zebrafish.