Chromosomal structure is altered by mutations that suppress or enhance position effect variegation

Area of Science:

• Genetics
• Molecular Biology
• Developmental Biology

Background:

• Position effect variegation (PEV) is a phenomenon in Drosophila where gene expression is altered due to relocation near heterochromatin.
• Suppressor of variegation (Su(var)) and enhancer of variegation (E(var)) mutations modulate PEV, affecting gene activity and chromatin structure.

Purpose of the Study:

• To investigate the genetic, morphological, and molecular impacts of PEV in Drosophila.
• To analyze the effects of Su(var) and E(var) mutations on PEV and associated gene expression.

Main Methods:

• Genetic analysis of Su(var) and E(var) mutations.
• Morphological examination of polytene chromosomes using in situ hybridization.
• Molecular analysis including DNA blot hybridization and DNAse I digestion.

Main Results:

• Su(var) mutations suppressed variegation of white, brown, and Stubble genes, while E(var) enhanced it.
• Su(var) mutations restored euchromatic morphology to heterochromatic regions containing variegating genes.
• DNA accessibility of the white gene correlated with variegation status, not gene copy number, indicating chromatin packaging is key.

Conclusions:

• PEV and the action of Su(var) mutations involve alterations in chromosomal packaging, impacting gene expression.
• Chromosomal packaging, rather than gene copy number, is the primary determinant of gene expression changes in PEV.