Origin and evolution of new exons in rodents.
Gene number difference among organisms demonstrates that new gene origination is a fundamental biological process in evolution. Exon shuffling has been universally observed in the formation of new genes. Yet to be learned are the ways new exons originate and evolve, and how often new exons appear. To address these questions, we identified 2695 newly evolved exons in the mouse and rat by comparing the expressed sequences of 12,419 orthologous genes between human and mouse, using 743,856 pig ESTs as the outgroup. The new exon origination rate is about 2.71 x 10(-3) per gene per million years. These new exons have markedly accelerated rates both of nonsynonymous substitutions and of insertions/deletions (indels). A much higher proportion of new exons have K(a)/K(s) ratios >1 (where K(a) is the nonsynonymous substitution rate and K(s) is the synonymous substitution rate) than do the old exons shared by human and mouse, implying a role of positive selection in the rapid evolution. The majority of these new exons have sequences unique in the genome, suggesting that most new exons might originate through "exonization" of intronic sequences. Most of the new exons appear to be alternative exons that are expressed at low levels.
Wang
Wen
W
CAS-Max Planck Junior Research Group, Key Laboratory of Cellular and Molecular Evolution, Kunming Institute of Zoology, Chinese Academy of Sciences, Kunming, Yunnan 650223, China. wwang@mail.kiz.ac.cn
Zheng
Hongkun
H
Yang
Shuang
S
Yu
Haijing
H
Li
Jun
J
Jiang
Huifeng
H
Su
Jianning
J
Yang
Lei
L
Zhang
Jianguo
J
McDermott
Jason
J
Samudrala
Ram
R
Wang
Jian
J
Yang
Huanming
H
Yu
Jun
J
Kristiansen
Karsten
K
Wong
Gane Ka-Shu
GK
Wang
Jun
J
D017398:Alternative Splicing; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000235:genetics; D019143:Evolution, Molecular; D005091:Exons; D020224:Expressed Sequence Tags; D006801:Humans; D007438:Introns; D051379:Mice; D010802:Phylogeny; D051381:Rats; D012377:Rodentia / Q000235:genetics*; D017384:Sequence Deletion; D012689:Sequence Homology, Nucleic Acid; D013045:Species Specificity; D013997:Time Factors
D004247:DNA