title: Smelt was the likely beneficiary of an antifreeze gene laterally transferred between fishes.
abstract: BACKGROUND
  Type II antifreeze protein (AFP) from the rainbow smelt, Osmerus mordax, is a calcium-dependent C-type lectin homolog, similar to the AFPs from herring and sea raven. While C-type lectins are ubiquitous, type II AFPs are only found in a few species in three widely separated branches of teleost fishes. Furthermore, several other non-homologous AFPs are found in intervening species. We have previously postulated that this sporadic distribution has resulted from lateral gene transfer. The alternative hypothesis, that the AFP evolved from a lectin present in a shared ancestor and that this gene was lost in most species, is not favored because both the exon and intron sequences are highly conserved.
  
  
  RESULTS
  Here we have sequenced and annotated a 160 kb smelt BAC clone containing a centrally-located AFP gene along with 14 other genes. Quantitative PCR indicates that there is but a single copy of this gene within the smelt genome, which is atypical for fish AFP genes. The corresponding syntenic region has been identified and searched in a number of other species and found to be devoid of lectin or AFP sequences. Unlike the introns of the AFP gene, the intronic sequences of the flanking genes are not conserved between species. As well, the rate and pattern of mutation in the AFP gene are radically different from those seen in other smelt and herring genes.
  
  
  CONCLUSIONS
  These results provide stand-alone support for an example of lateral gene transfer between vertebrate species. They should further inform the debate about genetically modified organisms by showing that gene transfer between 'higher' eukaryotes can occur naturally. Analysis of the syntenic regions from several fishes strongly suggests that the smelt acquired the AFP gene from the herring.
authors.affiliation: Department of Biomedical and Molecular Sciences, Queen's University, Kingston, ON K7L 3N6, Canada.
authors.forename: Laurie A
authors.initials: LA
authors.lastname: Graham
authors.forename: Jieying
authors.initials: J
authors.lastname: Li
authors.forename: William S
authors.initials: WS
authors.lastname: Davidson
authors.forename: Peter L
authors.initials: PL
authors.lastname: Davies
mesh_terms: D000818:Animals; D021341:Antifreeze Proteins, Type II / Q000235:genetics*; D001483:Base Sequence; D022202:Chromosomes, Artificial, Bacterial; D019143:Evolution, Molecular; D020224:Expressed Sequence Tags; D029941:Fish Proteins / Q000235:genetics*; D022761:Gene Transfer, Horizontal; D037181:Lectins, C-Type / Q000235:genetics; D058977:Molecular Sequence Annotation; D008969:Molecular Sequence Data; D036441:Osmeriformes / Q000235:genetics*; D010802:Phylogeny; D017422:Sequence Analysis, DNA
chemical_list: D021341:Antifreeze Proteins, Type II; D029941:Fish Proteins; D037181:Lectins, C-Type