title: The diversification of the LIM superclass at the base of the metazoa increased subcellular complexity and promoted multicellular specialization.
abstract: BACKGROUND
  Throughout evolution, the LIM domain has been deployed in many different domain configurations, which has led to the formation of a large and distinct group of proteins. LIM proteins are involved in relaying stimuli received at the cell surface to the nucleus in order to regulate cell structure, motility, and division. Despite their fundamental roles in cellular processes and human disease, little is known about the evolution of the LIM superclass.
  
  
  RESULTS
  We have identified and characterized all known LIM domain-containing proteins in six metazoans and three non-metazoans. In addition, we performed a phylogenetic analysis on all LIM domains and, in the process, have identified a number of novel non-LIM domains and motifs in each of these proteins. Based on these results, we have formalized a classification system for LIM proteins, provided reasonable timing for class and family origin events; and identified lineage-specific loss events. Our analysis is the first detailed description of the full set of LIM proteins from the non-bilaterian species examined in this study.
  
  
  CONCLUSIONS
  Six of the 14 LIM classes originated in the stem lineage of the Metazoa. The expansion of the LIM superclass at the base of the Metazoa undoubtedly contributed to the increase in subcellular complexity required for the transition from a unicellular to multicellular lifestyle and, as such, was a critically important event in the history of animal multicellularity.
authors.affiliation: Genome Technology Branch, National Human Genome Research Institute, National Institutes of Health, Bethesda, Maryland, United States of America.
authors.forename: Bernard J
authors.initials: BJ
authors.lastname: Koch
authors.forename: Joseph F
authors.initials: JF
authors.lastname: Ryan
authors.forename: Andreas D
authors.initials: AD
authors.lastname: Baxevanis
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001499:Bayes Theorem; D019143:Evolution, Molecular; D049810:Genetic Speciation; D014644:Genetic Variation; D006801:Humans; D060588:LIM Domain Proteins / Q000737:chemistry / Q000145:classification* / Q000235:genetics*; D016013:Likelihood Functions; D008957:Models, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D017386:Sequence Homology, Amino Acid
chemical_list: D060588:LIM Domain Proteins