shavenbaby shadow enhancers contribute to phenotypic robustness

FRANKEL N; DAVIS GK; VARGAS D; WANG S; PAYRE F; STERN DL

Washington DC

Congreso; 51st Drosophila Research Conference; 2010

Eukaryotic genes contain transcriptional enhancers that are often divided into discrete cis-regulatory modules. Recent reports have shown that many developmental genes possess multiple enhancers that drive transcription in similar spatio-temporal patterns: primary enhancers located near the basal promoter and secondary, or "shadow", enhancers located further from the basal promoter. The function of shadow enhancers is unknown; it has been hypothesized that they contribute to phenotypic robustness. We tested this hypothesis by generating a deficiency that removes two newly-discovered shadow enhancers of shavenbaby (svb), a gene encoding a transcription factor that directs development of larval trichomes. At optimal temperatures for embryonic development, this deficiency causes minor phenotypic defects in larval trichome pattern. In embryos that develop at both low and high extreme temperatures, however, absence of these shadow enhancers leads to extensive loss of trichomes. These temperature-dependant defects can be rescued by a transgene containing one of the shadow enhancers regulating the transcription of svb cDNA. Thus, the defects caused by this deficiency result from loss of the shadow enhancers. Finally, removal of one copy of the wingless gene, which is required for normal trichome patterning, causes similar defects in only those flies deficient for the shadow enhancers. These results support the hypothesis that shadow enhancers contribute to phenotypic robustness in the face of environmental and genetic variability