Heterochromatin blocks constituting the entire short arms of acrocentric chromosomes of Azara's owl monkey: formation processes inferred from chromosomal locations

オーン プラコンチ・ナンペ チャイパセルチ・寺田祥子・平井百合子・コンソン シクルナト・平井啓久・古賀章彦*

ヨザルのアクロセントリック染色体の短腕は、全部または大部分がヘテロクロマチンである。このような状態に至った進化的な過程を推測することを目的とした。まずこのヘテロクロマチンの DNA 成分をクローンとして得て調べたところ、187 塩基対の単位からなる繰り返し配列であることがわかった。この配列を OwlRep とよぶことにした。続いて OwlRep の染色体上の場所を調べたところ、アクロセントリック染色体短腕に加え、少数のメタセントリック染色体のセントロメア周辺にも存在することがわかった。ただしセントロメアの片側のみであった。この分布様式から、つぎのような過程を推測するに至った。(1) 異なる染色体の間でのセントロメアの相互作用をを通して、OwlRep は他の染色体に移った。(2) 移った先では、テロメア領域のヘテロクロマチンとみなされて、OwlRep は増幅した。

DNA Research 20 (2013): accepted for publication.

Centromeres and telomeres of higher eukaryotes generally contain repetitive sequences, which often form pericentric or subtelomeric heterochromatin blocks. C-banding analysis of chromosomes of Azara's owl monkey, a primate species, showed that the short arms of acrocentric chromosomes consist mostly or solely of constitutive heterochromatin. The purpose of the present study was to determine which category, pericentric or subtelomeric, is most appropriate for this heterochromatin, and to infer its formation processes. We cloned and sequenced its DNA component, finding it to be a tandem repeat sequence comprising 187-bp repeat units, which we named OwlRep. Subsequent hybridization analyses revealed that OwlRep resides in the pericentric regions of a small number of metacentric chromosomes, in addition to the short arms of acrocentric chromosomes. Further, in the pericentric regions of the acrocentric chromosomes, OwlRep was observed on the short-arm side only. This distribution pattern of OwlRep among chromosomes can be simply and sufficiently explained by assuming (i) OwlRep was transferred from chromosome to chromosome by interaction of pericentric heterochromatin, and (ii) it was amplified there as subtelomeric heterochromatin. OwlRep carries several direct and inverted repeats within its repeat units. This complex structure may lead to a higher frequency of chromosome scission, and thus may be a factor in the unique distribution pattern among chromosomes. Neither OwlRep nor similar sequences were found in the genomes of the other New World monkey species we examined, suggesting that OwlRep underwent rapid amplification after the divergence of the owl monkey lineage from lineages of the other species.

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