WHITE AS A REPORTER GENE TO DETECT TRANSCRIPTIONAL SILENCERS SPECIFYING POSITION-SPECIFIC GENE-EXPRESSION DURING DROSOPHILA-MELANOGASTER EYE DEVELOPMENT

The white(+) gene was used as a reporter to detect transcriptional sil encer activity in the Drosophila genome. Changes in the spatial expres sion pattern of while were scored in the adult eye as nonuniform patte rns of pigmentation. Thirty-six independent P[lacW] transposant lines were collected. These represent 12 distinct pigmentation patterns and probably 21 loci. The spatial pigmentation pattern is due to cis-actin g suppression of white(+) expression, and the suppression probably dep ends on cell position rather than cell type The mechanism of suppressi on differs from inactivation by heterochromatin. In addition, activati on of lacZ in P[lacW] occurs also in specific patterns in imaginal dis cs and embryos in many of the lines. The expression patterns of white( +) and IacZ may reflect the activity of regulatory elements belonging to an endogenous gene near each P[lacW] insertion site. We speculate t hat these putative POSE (position-specific expression) genes may have a role in pattern formation of the eye as well as other imaginal struc tures. Three of the loci identified are optomotor-blind, engrailed and invected. teashirt is also implicated as a candidate gene. We propose that this ''silencer trap'' may be an efficient way of identifying ge nes involved in imaginal pattern formation.