INTERACTIONS AMONG DOSAGE-DEPENDENT TRANS-ACTING MODIFIERS OF GENE-EXPRESSION AND POSITION-EFFECT VARIEGATION IN DROSOPHILA

We have investigated the effect of dosage-dependent trans-acting regul ators of the white eye color gene in combinations to understand their interaction properties. The consequences of the interactions will aid in an understanding of aneuploid syndromes, position-effect variegatio n (PEV), quantitative traits, and dosage compensation, all of which ar e affected by dosage-dependent modifiers. Various combinations modulat e two functionally related transcripts, white and scarlet, differently . The overall trend is that multiple modifiers are noncumulative or ep istatic to each other. In some combinations, developmental transitions from larvae to pupae to adults act as a switch for whether the effect is positive or negative. With position-effect variegation, similar re sponses were found as with gene expression. The highly multigenic natu re of dosage-sensitive modulation of both gene expression and PEV sugg ests that dosage effects can be progressively transduced through a ser ies of steps in a hierarchical manner.