Semester

Fall

Date of Graduation

1998

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Clifton P. Bishop.

Abstract

Position-effect variegation (PEV) describes the compaction of a euchromatic gene placed next to a region of heterochromatin. This compaction into heterochromatin in some instances results in a mosaic phenotype in Drosophila melanogaster. Since its discovery in the 1930's the phenomenon of PEV has been extensively analyzed and many models describing the mechanics have been proposed. But, until recently a model system for analyzing the phenomenon at various developmental stages was not available. In 1996, Lu, Bishop, and Eissenburg were able to use a transgenic construct that variegates for both a heat shock 70 promoter-driven lacZ construct and a mini-white gene, to allow more in-depth characterization of the developmental changes inherent in the formation of heterochromatin. The results of their research demonstrated that heterochromatic inactivation of gene expression is subject to a developmentally programmed derepression. Using this same construct, I have further characterized the phenomenon by classically constructing several genetic lines, which were either capable or incapable of initiating a heat shock response, but otherwise genetically identical. These lines were reared in both heat shock and non-heat shock conditions and then variegation was assessed by the amount of eye pigment deposited by the derepression of the mini-white gene. Our results indicate that derepression is a progressive event and that the expression of a nearby gene, Hsp-70 in this experimentation, can facilitate the derepression of nearby genes compressed into heterochromatin. It can be reasoned that this cooperative derepression may be playing a role in the expression of genes contained within B-heterochromatin. In this region there appears to be a dispersal of euchromatic genes around heterochromatic ones.

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