Analysis of the Inverse Effect in Drosophila

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Birchler9807802The long range goal of the proposed work is to understand the nature and mechanism of transacting regulatory genes that affect the expression of structural genes in a dosage sensitive manner, utilizing the white eye color locus of Drosophila melanogaster as a model system. It is believed that this type of regulatory effect is involved in the developmental expression of most types of structural genes in multicellular eukaryotes. Aneuploidy, or the change of individual chromosome number in an otherwise euploid genome, is associated with certain phenotypic consequences and it is thought that the dosage regulators play a significant role in the molecular basis of these syndromes. Previous work has identified several genes that produce a dosage sensitive modifying effect on white expression. Cloning, or other means of identifying these genes, revealed them to be various types of transcriptional factors and chromatin components. The major type of dosage effect is an inverse correlation between the copy number of the regulator and the expression of the target locus. If the regulator and the target are varied together, the effects cancel to produce dosage compensation. In the proposed work, a study of the interactions of 20 molecularly defined regulatory genes that are effective on white will establish what types of regulatory genes predominate in establishing the overall level of gene expression when several regulators are varied together as would occur in large aneuploids. This information will be of value for understanding regulatory gene circuitry, aneuploid syndromes, dosage compensation mechanisms and involvement of regulatory genes in the control of quantitative traits. The second major direction will be to analyze a newly discovered global regulatory complex that appears to exist throughout multicellular eukaryotes. The orthologous complex acts in yeast as a global negative regulatory system, but there are significant differences in the predicted protein sequences and action in Drosophila. The functional tests proposed will begin work on how these genes produce their effect on gene expression in multicellular species. Lastly, evidence was found in the previous funding period for nucleation sites for the association of the male specific lethal (MSL) complex on the male X chromosome. The hypothesized nucleation site will be isolated and the mechanism by which it conditions binding to the X will be studied. These experiments will address how the MSL proteins act to modify the action of the dosage sensitive regulatory genes. The proposed project will contribute to an understanding of inverse dosage regulation and address whether there is a connection between the responsible regulatory genes and the biological effects associated with chromosomal dosage such as compensation, quantitative traits, aneuploid syndromes and position effect variegation.A genome is more than a series of individual genes. It is a unit whose control of cell and organismal function is the result of complex interactions of those individual genes in a precise and patterned choreography. This work will give greater insight into some of those interactions and how they affect the regulation of individual target loci.