A detailed understanding of how genes are expressed and regulated in different tissues can help elucidate the molecular mechanisms of tissue development and function. The approximately 25,000 genes in the human genome demonstrate dramatic diversity in terms of expression levels, both temporally and spatially. Despite this diversity, the expression of all genes is controlled by a relatively small number (<2,000) of transcription factors (TFs). These TFs usually work in specific combination to regulate individual genes [2,3]. A number of databases have been created to facilitate studies of gene expression and regulation. For example, dbEST [4] is a database of expressed sequence tags (ESTs) from a number of organisms; GNF SymAtlas [5] and BodyMap [6] are databases that store human and mouse tissue gene expression profiles; TRANSFAC, TRANSCOMPEL and TRED [7,8] are databases that store information about transcriptional regulation. Some databases, such as CGED [9] and PEDB [10], allow users to access gene expression information derived from either human cancer tissues or one particular tissue (e.g., prostate). However, for a researcher who is interested in tissue-specific gene regulation and would like to examine possible cis-regulatory elements for a gene, a database dedicated to comprehensive information about tissue-specific gene regulation is desirable.
