Rate of evolution in brain-expressed genes in humans and other primates.
Brain-expressed genes are known to evolve slowly in mammals. Nevertheless, since brains of higher primates have evolved rapidly, one might expect acceleration in DNA sequence evolution in their brain-expressed genes. In this study, we carried out full-length cDNA sequencing on the brain transcriptome of an Old World monkey (OWM) and then conducted three-way comparisons among (i) mouse, OWM, and human, and (ii) OWM, chimpanzee, and human. Although brain-expressed genes indeed appear to evolve more rapidly in species with more advanced brains (apes > OWM > mouse), a similar lineage effect is observable for most other genes. The broad inclusion of genes in the reference set to represent the genomic average is therefore critical to this type of analysis. Calibrated against the genomic average, the rate of evolution among brain-expressed genes is probably lower (or at most equal) in humans than in chimpanzee and OWM. Interestingly, the trend of slow evolution in coding sequence is no less pronounced among brain-specific genes, vis-à-vis brain-expressed genes in general. The human brain may thus differ from those of our close relatives in two opposite directions: (i) faster evolution in gene expression, and (ii) a likely slowdown in the evolution of protein sequences. Possible explanations and hypotheses are discussed.
Wang
Hurng-Yi
HY
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan.
Chien
Huan-Chieh
HC
Osada
Naoki
N
Hashimoto
Katsuyuki
K
Sugano
Sumio
S
Gojobori
Takashi
T
Chou
Chen-Kung
CK
Tsai
Shih-Feng
SF
Wu
Chung-I
CI
Shen
C-K James
CK
D000818:Animals; D005075:Biological Evolution; D001921:Brain / Q000378:metabolism*; D003001:Cloning, Molecular; D018076:DNA, Complementary; D015870:Gene Expression; D006801:Humans; D011323:Primates / Q000235:genetics*
D018076:DNA, Complementary