Evolutionary Origin of Higher-Order Repeat Structure in Alpha-Satellite DNA of Primate Centromeres

Koga A, Hirai Y, Terada S, Jahan I, Baicharoen S, Arsaithamkul V, Hirai H (2014)

古賀章彦・平井百合子・寺田祥子・イスラット ジャハン・スダラ バイシャルン・ウィシット アサイタムクン・平井啓久

アルファサテライトＤＮＡは、霊長類のセントロメアを構成する反復配列である。ヒト科では、アルファサテライトＤＮＡは複雑な高次構造をとる。ヒト科以外では、高次構造の明瞭な例はみつかっていない。このため、ヒト科とテナガザル科が分岐した後にヒト科の系統で高次構造は生じたと、広く考えられている。我々は、高次構造を検出するための実験手法を開発し、テナガザル科で高次構造を見出した。テナガザル科には４属あり、４属すべてで明瞭な例を得た。この結果から、高次構造の進化的起源に関して、つぎのとぢらかの推測が成り立つ。(1) 高次構造はヒト上科の最後の共通祖先に存在していた。(2) 高次構造はヒト上科の基部をなす分類群のすべてまたはほとんどで生じた。 

DNA Res.earch (2014) Advance Access. doi: 10.1093/dnares/dsu005

Alpha-satellite DNA (AS) is a main DNA component of primate centromeres, consisting of tandemly repeated units of ∼170 bp. The AS of humans contains sequences organized into higher-order repeat (HOR) structures, in which a block of multiple repeat units forms a larger repeat unit and the larger units are repeated tandemly. The presence of HOR in AS is widely thought to be unique to hominids (family Hominidae; humans and great apes). Recently, we have identified an HOR-containing AS in the siamang, which is a small ape species belonging to the genus Symphalangus in the family Hylobatidae. This result supports the view that HOR in AS is an attribute of hominoids (superfamily Hominoidea) rather than hominids. A single example is, however, not sufficient for discussion of the evolutionary origin of HOR-containing AS. In the present study, we developed an efficient method for detecting signs of large-scale HOR and demonstrated HOR of AS in all the three other genera. Thus, AS organized into HOR occurs widely in hominoids. Our results indicate that (i) HOR-containing AS was present in the last common ancestor of hominoids or (ii) HOR-containing AS emerged independently in most or all basal branches of hominoids. We have also confirmed HOR occurrence in centromeric AS in the Hylobatidae family, which remained unclear in our previous study because of the existence of AS in subtelomeric regions, in addition to centromeres, of siamang chromosomes.

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