Imprinting in Drosophila: Quantitative Evaluation of Parent-of-Origin Phenotypic Effects Through Transmission of Fab-7 Boundary Element Deletions

Abstract

In many multicellular eukaryotic organisms, chromatin boundary elements subdivide chromosomes into topologically autonomous domains of genetic activity. While the mechanism behind boundary assembly is not well understood, it is well documented that loss of boundary activity has severe phenotypic effects. The Drosophila melanogaster boundary element Fab-7 binds various boundary-specific protein factors that assist its function as an insulator for the iab-6 and iab-7 regulatory domains. This insulation function ensures proper regulation of Abd-b expression in parasegments 11 and 12 which are expressed in adult flies as abdominal segments A5 and A6, respectively. Abrogation of Fab-7 boundary function is associated with loss of abdominal segment A6 expression in adult males. Interestingly, we observed a parent-of-origin effect on A6 segment area in heterozygotic progeny who inherited a ΔFab-7attP boundary deletion. We used quantitative analysis and qualitative comparison to find that differences in A6 segment area among genetically identical F1 male adults are statistically significant. We also found that inheritance of the ΔFab-7attP and ΔFab-728 boundary deletions was associated with more severe A6 size reduction phenotypes when it was maternally transmitted than when it was paternally transmitted. Thus, the observational evidence gathered in this investigation provides support for the existence of transgenerational epigenetic inheritance, possible through histone and/or DNA methylation mechanisms, in Drosophila melanogaster.