P transposon-induced dominant enhancer mutations of position-effect variegation in Drosophila melanogaster

Abstract

P transposon induced modifier mutations of position-effect variegation (PEV) were isolated with the help of hybrid dysgenic crosses (7r2 strain) and after transposition of the mutator elements pUChsneory+ and P [IArB]. Enhancer mutations were found with a ten times higher frequency than suppressors. The 19 pUChsneory+-and 15 P[lArB]-induced enhancer mutations can be used for cloning of genomic sequences at the insertion sites of the mutator elements via plasmid rescue. Together with a large sample of X-ray-induced (48) and spontaneous (93) enhancer mutations a basic genetic analysis of this group of modifier genes was performed. On the basis of complementation and mapping data we estimate the number of enhancer genes at about 30 in the third chromosome and between 50 and 60 for the whole autosome complement. Therefore, enhancer of PEV loci are found in the Drosophila genome as frequently as suppressor genes. Many of the enhancer mutations display paternal effects consistent with the hypothesis that some of these mutations can induce genomic imprinting. First studies on the developmentally regulated gene expression of PEV enhancer genes were performed by &plactosidase staining in P [IArB] al. 1986; SINCLAIR, LLOYD and GRIG-LIATTI 1989). In these studies the total number of PEV modifier genes in the Drosophila genome was estimated to be about 100-1 20 (HENIKOFF 1979;WUSTMANN et al. 1989). By studying their dosagedependent effects four classes of genes have been distinguished: in one class of genes a deficiency causes suppression (haplo-suppressors) and in another group of loci a deficiency displays an enhancer effect (haploenhancers). For some genes of both classes a duplication was found to result in an opposite triplo-effect (haplo-suppressors with a triplo-enhancer effect and haplo-enhancers with a triplo-suppressor effect