Evolutionary genomics of nuclear receptors: from 25 ancestral genes to derived endocrine systems (original) (raw)

Bilaterian animals are notably characterized by complex endocrine systems. The receptors for many steroids, retinoids, and other hormones, belong to the superfamily of nuclear receptors, which are transcription factors regulating many aspects of development and homeostasis. Despite a diversity of regulatory mechanisms and of physiological roles, nuclear receptors share a common protein organization. To obtain the broad picture of bilaterian nuclear hormone receptor evolution, we have characterized the complete set of nuclear receptor genes from nine animal genome sequences, and analyzed it in a phylogenetic framework. In addition, Expressed Sequence Tags from key lineages with no available genome sequence were also searched. This allows us to date the evolutionary events which led from an ancestral nuclear receptor gene, in an early metazoan, to present day diversity. We show that there were ca. 25 nuclear receptor genes in Urbilateria, the ancestor of bilaterians, at which point the fundamental diversity of the subfamily was already established.