Sea urchin Forkhead gene family: phylogeny and embryonic expression.

Transcription factors of the Forkhead (Fox) family have been identified in many metazoans, and play important roles in diverse biological processes. Here we define the set of fox genes present in the sea urchin genome, and survey their usage during development. This genome includes 22 fox genes, only three of which were previously known. Of the 23 fox gene subclasses identified in vertebrate genomes, the Strongylocentrotus purpuratus genome has orthologues of all but four (E, H, R and S). Phylogenetic analysis suggests that one S. purpuratus fox gene is equally related to foxA and foxB of vertebrates; this gene defines a new class. Two other genes appear to be specific to the sea urchin, with respect to the genomes so far sequenced. Fox genes orthologous with those of vertebrates but lacking in arthropod or nematode genomes may be deuterostome-specific (subclasses I, J1, J2, L1, M and Q1), while the majority are pan-bilaterian. All but one of the S. purpuratus fox genes (SpfoxQ1) are expressed during embryogenesis, most in a very specific temporal and spatial manner. The sea urchin fox genes clearly execute many different regulatory functions, and almost all of them participate in the process of embryonic development.