THE LIGHTEN UP (LIP) GENE OF DROSOPHILA-MELANOGASTER, A MODIFIER OF RETROELEMENT EXPRESSION, POSITION EFFECT VARIEGATION AND WHITE LOCUS INSERTION ALLELES

We are interested in identifying single gene mutations that are involv ed in trans-acting dosage regulation in order to understand further th e role of such genes in aneuploid syndromes, various types of dosage c ompensation as well as in regulatory mechanisms. The Lighten up (Lip) gene in Drosophila melanogaster was identified in a mutagenic screen t o detect dominant second site modifiers of white-blood (W-bl), a retro transposon induced allele of the white eye color locus. Lip specifical ly enhances the phenotype of w(bl) as well as a subset of other retroe lement insertion alleles of white, including the copia-induced allele, white-apricot (w(a)), and six alleles caused by insertion of I elemen ts. We isolated six alleles of Lip which are all recessive lethal, alt hough phenotypically additive heteroallelic escapers were recovered in some combinations. Lip also suppresses position effect variegation, i ndicating that it may have a role in chromatin configuration. Addition ally, Lip modifies the total transcript abundance of both the blood an d copia retrotransposons, having an inverse effect on the steady state level of blood transcripts, while showing a non-additive effect on co pia RNA.