Fig. 1. Rx3 expression in wild-type and el-mutant embryos. Dorsal views of whole-mount in situ hybridisation of late gastrula (stage 16; A,B) and four-somite stage (stage 20; C,D) wild type (A,C) and el-mutant embryos kept at restrictive temperature (B,D). Anterior is towards the left. Neural axis is indicated by a broken yellow line (A,B). (A) Rx3 expression in anterior neural plate. (C) Rx3 expression in hypothalamus (arrow) and optic cup (arrowhead). (B,D). Note complete loss of Rx3 expression in mutant embryos kept under restrictive conditions. (F) Under permissive conditions, Rx3 is weakly expressed in forebrain of el-mutant embryos at the two-somite stage (stage 19). Note reduced size of evaginating optic vesicles (arrowhead) at site of reduced Rx3 expression compared with wild-type embryo of same stage (arrowhead in E). (G) Primers spanning entire open reading frame detect the wild-type transcript by RT-PCR in wild-type (lane 1) and el-mutant embryos (lane 2) under permissive conditions, while no transcript is detected in mutants under restrictive conditions (lane 3). M, 100 bp ladder. Abbreviations: perm., permissive temperature; restr., restrictive temperature.