Nanda Indrajit, Schrama David, Feichtinger Wolfgang, Haaf Thomas, Schartl Manfred, Schmid Michael
Department of Human Genetics, University of Würzburg, Würzburg, Germany.
Chromosoma. 2002 Nov;111(4):215-27. doi: 10.1007/s00412-002-0206-4. Epub 2002 Sep 24.
The physical ends of mammalian and other vertebrate chromosomes consist of tandemly repeated (TTAGGG)(n) hexamers, nucleating a specialized telomeric structure. However, (TTAGGG)(n) sequences can also occur at non-telomeric sites, providing important insights into karyotypic evolution. By fluorescence in situ hybridization (FISH) we studied the chromosomal distribution of (TTAGGG)(n) sequences in 16 bird species, representing seven different orders. Many species, in particular the ratites, display (TTAGGG)(n) hybridization signals in interstitial and centromeric regions of their macrochromosomes in addition to the typical telomeric signals. In some but not all species these non-telomeric sites coincide with C-band-positive heterochromatin. The retention and/or amplification of telomeric (TTAGGG)(n) repeats at interstitial and centromeric sites may indicate the fusion of ancestral chromosomes. Compared with the macrochromosomes, the microchromosomes of most species are enriched with (TTAGGG)(n) sequences, displaying heterogeneous hybridization patterns. We propose that this high density of (TTAGGG)(n) repeats contributes to the exceptionally high meiotic recombination rate of avian microchromosomes.
哺乳动物和其他脊椎动物染色体的物理末端由串联重复的（TTAGGG）（n）六聚体组成，形成一种特殊的端粒结构。然而，（TTAGGG）（n）序列也可能出现在非端粒位点，这为核型进化提供了重要见解。通过荧光原位杂交（FISH）技术，我们研究了16种鸟类（代表七个不同目）中（TTAGGG）（n）序列的染色体分布。许多物种，特别是平胸鸟类，除了典型的端粒信号外，在其常染色体的间质和着丝粒区域也显示出（TTAGGG）（n）杂交信号。在一些但并非所有物种中，这些非端粒位点与C带阳性异染色质重合。间质和着丝粒位点端粒（TTAGGG）（n）重复序列的保留和/或扩增可能表明祖先染色体的融合。与常染色体相比，大多数物种的微染色体富含（TTAGGG）（n）序列，呈现出异质的杂交模式。我们认为，这种高密度的（TTAGGG）（n）重复序列导致了鸟类微染色体极高的减数分裂重组率。
