AQUARIUS, A NOVEL GENE ISOLATED BY GENE TRAPPING WITH AN RNA-DEPENDENT RNA-POLYMERASE MOTIF

In a retinoic acid (RA) gene-trap screen of mouse embryonic stem (ES) cells, a novel gene, named Aquarius (Aqr), was identified and characte rized. The promoterless lacZ marker was used to trap the genomic locus and to determine the expression pattern of the gene. Aqr transcripts are strongly induced in response to RA in vitro. During embryogenesis, Aqr is expressed in mesoderm, in the neural crest and its target tiss ues, and in neuroepithelium, Expression was first detected at 8.5 days postcoitum, when neural crest cells are visible at the lateral ridges of the neural plate. The gene-trapped Aqr locus was transmitted throu gh the mouse germ line in three genetic backgrounds. In the F2 generat ion, the expected mendelian ratio of 1:2:1 was observed in all backgro unds, indicating that homozygous mice are viable. Homozygotes are norm al in size and weight and breed normally, The gene trap insertion, how ever, does not seem to generate a null mutation, because Aqr transcrip ts are still present in the homozygous mutant animals. The Aqr open re ading frame has weak homology to RNA-dependent RNA polymerases (RRPs) of the murine hepatitis viruses and contains an RRP motif. Aqr was map ped to mouse chromosome 2 between regions E5 through F2 by using fluor escence in situ hybridization analysis. (C) 1998 Wiley-Liss, Inc.