It is becoming increasing apparent that eukaryotic genomes are organized into regions containing clusters of co-regulated genes. In the August 29 Nature, Peter Roy and colleagues describe clusters of muscle-expressing genes in the Caenorhabditiselegans genome (Nature 2002, 418:975-979).

Roy et al. developed a method called 'messenger RNA tagging' that uses immunoprecipitation of an epitope-tagged RNA-binding protein to purify mRNA expressed in different tissues; they then used DNA microarrays to analyze the enrichment of co-immunoprecipitated mRNAs. Roy et al. found over 1,000 genes that were consistently enriched in six muscle mRNA-tagging experiments. When they mapped the chromosomal locations of these genes, they found that almost a third of them are positioned within 10kb of another muscle-expressed gene. Many of the muscle genes are found in clusters of 2-5 genes, sometimes interrupted by a non-expressed gene. Additional analysis provided evidence for clustering of genes expressed in sperm...