Tracking the sequences of regulatory linkages and their evolution within a fruit fly gene regulatory network

Date of Award


Degree Name

M.S. in Biology


Department of Biology


Advisor: Thomas Williams


Phenotypes are the culmination of the spatial and temporal patterns of gene expression for numerous genes that comprise a gene regulatory network (GRN). These patterns are controlled by cis-regulatory elements (CREs). Genes are connected into GRNs when a CRE regulating its expression possess binding sites for network transcription factor proteins - so called regulatory linkages. Gains and losses of these linkages are candidates for a mechanistic path of CRE and GRN evolution; though linkage emergence remains poorly understood, as few case studies have revealed the ancestral and derived regulatory states in sufficient detail. The male-specific abdominal pigmentation of Drosophila melanogaster evolved from a sexually monomorphic ancestral state, with a key modification to the pigmentation GRN being the evolution of sexually dimorphic expression of the Bab transcription factor proteins. These proteins turn off expression of the yellow and tan genes that are required for melanic abdominal pigmentation. The research presented here addresses two questions. First, does Bab form direct regulatory linkages with the CRE(s) that control the male-specific expression of the Drosophila melanogaster yellow and tan genes? Second, when historically did these CREs and their regulatory linkages evolve? To answer these questions I: systematically mutated CRE sequences to expose motifs needed to integrate the repressive effects of Bab, and evaluated the regulatory activities of sequences related by common descent to the Drosophila melanogaster CREs. The results reveal the complex CRE encodings of putative Bab linkages and that these CREs and linkages evolved in the lineage of dimorphic species after it diverged from the lineage of monomorphic species. Future studies are needed to determine whether this divergence included the gain of Bab binding sites in the CREs of dimorphic species.


Drosophila melanogaster Genetics, Drosophila melanogaster Color, Gene regulatory networks, Yellow; tan; Drosophila; evolution; CRE; enhancers; genetics

Rights Statement

Copyright © 2012, author