Medaka: a promising model animal for comparative population genomics.
BACKGROUND
Within-species genome diversity has been best studied in humans. The international HapMap project has revealed a tremendous amount of single-nucleotide polymorphisms (SNPs) among humans, many of which show signals of positive selection during human evolution. In most of the cases, however, functional differences between the alleles remain experimentally unverified due to the inherent difficulty of human genetic studies. It would therefore be highly useful to have a vertebrate model with the following characteristics: (1) high within-species genetic diversity, (2) a variety of gene-manipulation protocols already developed, and (3) a completely sequenced genome. Medaka (Oryzias latipes) and its congeneric species, tiny fresh-water teleosts distributed broadly in East and Southeast Asia, meet these criteria.


RESULTS
Using Oryzias species from 27 local populations, we conducted a simple screening of nonsynonymous SNPs for 11 genes with apparent orthology between medaka and humans. We found medaka SNPs for which the same sites in human orthologs are known to be highly differentiated among the HapMap populations. Importantly, some of these SNPs show signals of positive selection.


CONCLUSIONS
These results indicate that medaka is a promising model system for comparative population genomics exploring the functional and adaptive significance of allelic differentiations.
Department of Integrated Biosciences, Graduate School of Frontier Sciences, University of Tokyo, Tokyo, Japan. miraihe08@brain.riken.jp
Yoshifumi
Y
Matsumoto
Hiroki
H
Oota
Yoichi
Y
Asaoka
Hiroshi
H
Nishina
Koji
K
Watanabe
Janusz M
JM
Bujnicki
Shoji
S
Oda
Shoji
S
Kawamura
Hiroshi
H
Mitani