SMN gene duplication and the emergence of the SMN2 gene occurred in distinct hominids: SMN2 is unique to Homo sapiens.
The spinal muscular atrophy (SMA) region on chromosome 5q13 contains an inverted duplication of about 500 kb, and deleterious mutations in the survival motor neuron 1 (SMN1) gene cause SMA, a common lethal childhood neuropathy. We have used a number of approaches to probe the evolutionary history of these genes and show that SMN gene duplication and the appearance of SMN2 occurred at very distinct evolutionary times. Molecular fossil and molecular clock data suggest that this duplication may have occurred as recently as 3 million years ago in that the position and identity repetitive elements are identical for both human SMN genes and overall sequence divergence ranged from 0.15% to 0.34%. However, these approaches ignore the possibility of sequence homogenization by means of gene conversion. Consequently, we have used quantitative polymerase chain rection and analysis of allelic variants to provide physical evidence for or against SMN gene duplication in the chimpanzee, mankind's closest relative. These studies have revealed that chimpanzees have 2-7 copies of the SMN gene per diploid genome; however, the two nucleotides diagnostic for exons 7-8 and the SMNdelta7 mRNA product of the SMN2 gene are absent in non-human primates. In contrast, the SMN2 gene has been detected in all extant human populations studied to date, including representatives from Europe, the Central African Republic, and the Congo. These data provide conclusive evidence that SMN gene duplication occurred more than 5 million years ago, before the separation of human and chimpanzee lineages, but that SMN2 appears for the first time in Homo sapiens.
Rochette
C F
CF
Centre de Recherche, H pital Sainte-Justine, Montréal, Québec, Canada.
Gilbert
N
N
Simard
L R
LR
D000483:Alleles; D000818:Animals; D001483:Base Sequence; D002461:Cell Line, Transformed; D017362:Cyclic AMP Response Element-Binding Protein; D004247:DNA / Q000737:chemistry / Q000235:genetics; D018076:DNA, Complementary / Q000737:chemistry / Q000235:genetics; D005260:Female; D020440:Gene Duplication; D014644:Genetic Variation; D006801:Humans; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics*; D002679:Pan troglodytes / Q000235:genetics; D011110:Polymorphism, Genetic; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein
D017362:Cyclic AMP Response Element-Binding Protein; D018076:DNA, Complementary; D009419:Nerve Tissue Proteins; D016601:RNA-Binding Proteins; D055532:SMN Complex Proteins; C526471:SMN1 protein, human; C526477:SMN2 protein, human; D055533:Survival of Motor Neuron 1 Protein; D055540:Survival of Motor Neuron 2 Protein; D004247:DNA