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Full Abstracts – REGULATION OF GENE EXPRESSION II
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Evolution of Transcriptional Regulation in Early Embryos of the Drosophila Genus.
Mathilde PARIS
1
, Tommy KAPLAN
1
, Susan LOTT
1
, Xiao-Yong
LI
2
, Jacqueline VILLALTA
2
, Michael EISEN
1,2
. 1) Molecular and Cellular Biology, QB3 Institute, BERKELEY, CA; 2) Howard Hughes Medical Institute,
University of California Berkeley, Berkeley, CA.
To better characterize how variation in regulatory sequences drives divergence in gene expression, we undertook a systematic study of transcription factor
binding and gene expression in four species that sample much of the diversity in the 60 million-year old genus Drosophila: D. melanogaster, D. yakuba, D.
pseudoobscura and D. virilis. We used ChIP-Seq to examine the genome-wide binding of four transcription factors (BCD, HB, GT and KR) regulating
segmentation along the anterior-posterior axis. As expected, genome-wide transcription factor binding divergence correlates with phylogenetic distance;
regions more highly bound in D. melanogaster were more likely to be bound in other species, and to have similar overall levels of binding; and
increases/decreases in binding were associated with gain/loss of transcription factor binding sites. To examine the consequences of these changes, we used
single embryo mRNA-Seq to measure gene expression in sex individual blastoderm embryos of each species. Surprisingly, we found relatively few changes
in gene expression, suggesting that differences in sequence and binding have limited effect on gene expression or act in a compensatory manner to maintain
the overall expression levels of regulated genes. Using in situ hybridization, we also compared the expression pattern of genes showing variation in nearby
regulatory TF binding among species. Finally, we used an evolutionary model of quantitative traits to link the evolution of gene expression with the
evolution of regulatory TF binding. This analysis unravels the evolutionary links between various levels of transcriptional regulation, from DNA sequence to
gene expression through protein binding.