Genomic, evolutionary, and expression analyses of cee, an ancient gene involved in normal growth and development

The cee (conserved edge expressed protein) gene was recently identified in a genome-wide screen to discover genes associated with myotube formation in fast muscle of pufferfish. Comparative genomic analyses indicate that cee arose some 1.6-1.8 billion years ago and is found as a single-copy gene in most eukaryotic genomes examined. The complexity of its structure varies from an intronless gene in yeast and tunicates to nine exons and eight introns in vertebrates. cee is particularly conserved among vertebrates and is located in a syntenic region within tetrapods and between teleosts and invertebrates. Low dN/dS ratios in the cee coding region (0.02-0.09) indicate that the Cee protein is under strong purifying selection. In Atlantic salmon, cee is expressed in the superficial layers of developing organs and tissues. These data, together with functional screens in yeast and Caenorhabditis elegans, indicate that cee has a hitherto uncharacterized role in normal growth and development.