Positional clustering of differentially expressed genes on human chromosomes 20, 21 and 22.

BACKGROUND: Clusters of genes co-expressed are known in prokaryotes (operons) and were recently described in several eukaryote organisms, including Human. According to some studies, these clusters consist of housekeeping genes, whereas other studies suggest that these clustered genes exhibit similar tissue specificity. Here we further explore the relationship between co-expression and chromosomal co-localization in the human genome by analyzing the expression status of the genes along the best-annotated chromosomes 20, 21 and 22. METHODS: Gene expression levels were estimated according to their publicly available ESTs and gene differential expressions were assessed using a previously described and validated statistical test. Gene sequences for chromosomes 20, 21 and 22 were taken from the Ensembl annotation. RESULTS: We identified clusters of genes specifically expressed in similar tissues along chromosomes 20, 21 and 22. These co-expression clusters occurred more frequently than expected by chance and may thus be biologically significant. CONCLUSION: The co-expression of co-localized genes might be due to higher chromatin structures influencing the gene availability for transcription in a given tissue or cell type.