A genetic screen for mutations affecting embryonic development in medaka fish (Oryzias latipes)

In a pilot screen, we assayed the efficiency of ethyinitrosourea (ENU) as a chemical mutagen to induce mutations that lead to early embryonic and larv al lethal phenotypes in the Japanese medaka fish, Oryzias latipes. ENU acts as a very efficient mutagen inducing mutations at high rates in germ cells . Three repeated treatments of male fish in 3 mM ENU for 1 h results in loc us specific mutation rates of 1.1-1.95 X 10(-3). Mutagenized males were out crossed to wild type females and the Fl offspring was used to establish F2 families. F2 siblings were intercrossed and the F3 progeny was scored 24, 4 8 and 72 h after fertilization for morphological alterations affecting eye development. The presented mutant phenotypes were identified using morpholo gical criteria and occur during early developmental stages of medaka. They are stably inherited in a Mendelian fashion. The high efficiency of ENU to induce mutations in this pilot screen indicates that chemical mutagenesis a nd screening for morphologically visible phenotypes in medaka fish allows t he genetic analysis of specific aspects of vertebrate development complemen ting the screens performed in other vertebrate model systems. (C) 2000 Else vier Science Ireland Ltd. All rights reserved.