Evolution and divergence of sodium channel genes in vertebrates.
Invertebrate species possess one or two Na+ channel genes, yet there are 10 in mammals. When did this explosive growth come about during vertebrate evolution? All mammalian Na+ channel genes reside on four chromosomes. It has been suggested that this came about by multiple duplications of an ancestral chromosome with a single Na+ channel gene followed by tandem duplications of Na+ channel genes on some of these chromosomes. Because a large-scale expansion of the vertebrate genome likely occurred before the divergence of teleosts and tetrapods, we tested this hypothesis by cloning Na+ channel genes in a teleost fish. Using an approach designed to clone all of the Na+ channel genes in a genome, we found six Na+ channel genes. Phylogenetic comparisons show that each teleost gene is orthologous to a Na+ channel gene or gene cluster on a different mammalian chromosome, supporting the hypothesis that four Na+ channel genes were present in the ancestors of teleosts and tetrapods. Further duplications occurred independently in the teleost and tetrapod lineages, with a greater number of duplications in tetrapods. This pattern has implications for the evolution of function and specialization of Na+ channel genes in vertebrates. Sodium channel genes also are linked to homeobox (Hox) gene clusters in mammals. Using our phylogeny of Na+ channel genes to independently test between two models of Hox gene evolution, we support the hypothesis that Hox gene clusters evolved as (AB) (CD) rather than [D[A(BC)]].
Lopreato
G F
GF
Sections of Neurobiology and Integrative Biology, School of Biological Sciences, University of Texas, Austin, TX 78712, USA.
Lu
Y
Y
Southwell
A
A
Atkinson
N S
NS
Hillis
D M
DM
Wilcox
T P
TP
Zakon
H H
HH
D000818:Animals; D002874:Chromosome Mapping; D019143:Evolution, Molecular; D005399:Fishes; D020131:Genes, Duplicate; D005801:Genes, Homeobox; D014644:Genetic Variation; D006801:Humans; D008958:Models, Molecular; D008969:Molecular Sequence Data; D009928:Organ Specificity; D010802:Phylogeny; D017433:Protein Structure, Secondary; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012455:Salamandridae; D015222:Sodium Channels / Q000737:chemistry / Q000235:genetics*; D014714:Vertebrates / Q000145:classification / Q000235:genetics*
D015222:Sodium Channels