Genome-Scale Analysis of Hematopoietic Regulatory Sequences by Digital Analysis of Chromatin Structure.

In vivo, cis-regulatory elements coincide with focal disruptions in chromatin structure that manifest as DNaseI hypersensitive sites (HSs). We developed a novel stochastic methodology for comprehensive, genome-wide mapping of DNaseI HSs in vivo. We show that 19–20bp genomic DNA tags can be used to effect genome-wide localization of individual DNaseI cutting events in nuclear chromatin, and that such tags can be generated and sequenced in large numbers from limited numbers of starting cells. We analyzed 257,000 tags from a hematopoietic cell line (K562) and applied a quantitative algorithm to discriminate statistically significant tag clustering events. Such tag clusters identified both known and novel functional elements of hematopoietic genes across the genome. A unique feature of this approach is that it permits unbiased evaluation of the chromatin context of regulatory sequences from disperse genomic loci. We observed surprisingly large differences in the chromatin structural configuration of a variety of active erythroid and hematopoietic regulatory sequences, suggesting a discrete hierarchy of nuclear organization that is not apparent with conventional assays. This approach can be applied readily to generate a comprehensive catalogue of cis-regulatory sequences active in hematopoietic stem cells.