Genome-wide transcriptome mapping analysis identifies organ-specific gene expression patterns along human chromosomes.

The Human Genome Project has revealed that there about 32,000 protein-encoding genes, which are distributed throughout the genome. It is unclear, however, whether genes are distributed on the chromosomes according to patterns linked to organ specificity. To explore the relationship between genes actively transcribed in normal tissues and their chromosomal locations, we analyzed serial analysis of gene expression libraries of normal human liver, brain, breast, and colon tissues. Transcriptome mapping analysis revealed that transcriptional activity in each tissue varied according to the chromosomal domains, and a weak positive correlation was observed between transcription density and gene density. We identified six liver-related and five colon-related chromosomal domains highly transcribed in each tissue, whereas no brain-related or breast-related chromosomal domains were identified. Representative genes located on these chromosomal domains were associated with the function of each organ and were highly conserved in both mouse and rat genomes. These data revealed that the transcriptional activities of normal human tissues are well orchestrated at chromosomal levels, suggesting that highly expressed genes may share physical proximity.