Tissue-specificity of Drosophila Developmental Gene Regulatory Networks. Matthew Slattery¹, Roumen Voutev², Rebecca Spokony¹, Lijia Ma¹, Richard Mann², Kevin White¹. 1) Institute for Genomics and Systems Biology, University of Chicago, Chicago, IL; 2) Department of Biochemistry and Molecular Biophysics, Columbia University, New York, NY.

   While a whole animal-based chromatin immunoprecipitation approach has been very successful at identifying cis-regulatory elements in Drosophila, an important question remains about what information will be gained by focusing on individual tissues. We have used genome-wide ChIP to map the binding patterns for selector genes, growth regulators and Polycomb group (PcG)-associated histone modifications in imaginal discs, progenitor tissues that give rise to limited subsets of the adult fly (eye, wing, etc.). Unlike ChIP experiments carried out using whole animals, which are composed of many different cell types, these experiments analyze the binding of these transcription factors in tissues with less cell-type complexity. Consistent with this limited amount of cell type diversity, and the fact that these tissues give rise to distinct parts of the adult fly, we found that the putative target genes regulated by these transcription factors and PcG display significant tissue-specificity. In many cases this specificity provides mechanistic or functional details that could not be gathered from whole animal-based approaches. However, all factors tested also display significant tissue 'common' binding -- binding shared across tissues -- and it appears that these common events can also be functionally relevant. Interestingly, regulators of developmental patterning show much more tissue-specific binding than general growth regulators, suggesting that focusing on individual tissues will be especially important for mapping out developmental gene regulatory networks.