title: Phylogenetic analysis of the human basic helix-loop-helix proteins.
abstract: BACKGROUND
  The basic helix-loop-helix (bHLH) proteins are a large and complex multigene family of transcription factors with important roles in animal development, including that of fruitflies, nematodes and vertebrates. The identification of orthologous relationships among the bHLH genes from these widely divergent taxa allows reconstruction of the putative complement of bHLH genes present in the genome of their last common ancestor.
  
  
  RESULTS
  We identified 39 different bHLH genes in the worm Caenorhabditis elegans, 58 in the fly Drosophila melanogaster and 125 in human (Homo sapiens). We defined 44 orthologous families that include most of these bHLH genes. Of these, 43 include both human and fly and/or worm genes, indicating that genes from these families were already present in the last common ancestor of worm, fly and human. Only two families contain both yeast and animal genes, and no family contains both plant and animal bHLH genes. We suggest that the diversification of bHLH genes is directly linked to the acquisition of multicellularity, and that important diversification of the bHLH repertoire occurred independently in animals and plants.
  
  
  CONCLUSIONS
  As the last common ancestor of worm, fly and human is also that of all bilaterian animals, our analysis indicates that this ancient ancestor must have possessed at least 43 different types of bHLH, highlighting its genomic complexity.
authors.affiliation: Evolution et Développement des protostomiens, Centre de Génétique moléculaire, UPR 2167 CNRS, 1 Ave de la terrasse, 91198 Gif-sur-Yvette Cedex, France. vervoort@cgm.cnrs-gif.fr
authors.forename: Valérie
authors.initials: V
authors.lastname: Ledent
authors.forename: Odier
authors.initials: O
authors.lastname: Paquet
authors.forename: Michel
authors.initials: M
authors.lastname: Vervoort
mesh_terms: D000818:Animals; D030161:Avian Proteins / Q000737:chemistry / Q000235:genetics; D017173:Caenorhabditis elegans; D002645:Chickens; D019295:Computational Biology; D030562:Databases, Protein; D004331:Drosophila melanogaster; D019143:Evolution, Molecular; D018257:Helix-Loop-Helix Motifs / Q000235:genetics*; D015801:Helminth Proteins / Q000737:chemistry / Q000235:genetics; D006801:Humans; D019476:Insect Proteins / Q000737:chemistry / Q000235:genetics; D051379:Mice; D010802:Phylogeny; D011506:Proteins / Q000737:chemistry / Q000235:genetics*
chemical_list: D030161:Avian Proteins; D015801:Helminth Proteins; D019476:Insect Proteins; D011506:Proteins