Manzanero S, Puertas M J, Jiménez G, Vega J M
Departamento de Genética, Facultad de Biología, Universidad Complutense, Madrid, Spain.
Chromosome Res. 2000;8(6):543-54. doi: 10.1023/a:1009275807397.
The neocentric activity of a constriction located on the long arm of rye 5R chromosome (5RL) was analysed. It is not observed in normal rye but it is unusually stretched in bivalents involving 5RL telosomes in wheat-ditelosomic 5RL addition lines. In 20% of metaphase I cells, the 5RL bivalent presents the centromeres oriented to one pole and the constrictions oriented towards the opposite pole with a strong tension. In 5% of the cells, the constriction was able to orient the bivalent to the poles without tension in the centromeres. Sister chromatid cohesion, which is one of the distinct features of centromeric function, is persistent at the constriction in delayed 5RL chromosomes at anaphase I. Neither the elongation of the constriction nor the neocentric activity was observed at second meiotic division or mitosis. FISH studies showed that the 5RL constriction lacked detectable quantities of two repetitive DNA sequences, CCS1 and the 180-bp knob repeat, present at cereal centromeres and neocentromeres, respectively. We propose that, under special conditions, such as the wheat background, the normally non-centromeric DNA present at this region of 5RL acquires a specific chromatin structure, differentiated as an elongated constriction, which is able to function as a centromere.
对位于黑麦5R染色体长臂（5RL）上的缢痕的新着丝粒活性进行了分析。在正常黑麦中未观察到这种缢痕，但在小麦-5RL端体附加系中，涉及5RL端体的二价体中它异常伸长。在20%的减数第一次分裂中期细胞中，5RL二价体的着丝粒朝向一极，缢痕朝向相反极且有强烈张力。在5%的细胞中，缢痕能够在着丝粒无张力的情况下将二价体导向两极。姐妹染色单体黏连是着丝粒功能的一个显著特征，在减数第一次分裂后期延迟的5RL染色体的缢痕处持续存在。在减数第二次分裂或有丝分裂中未观察到缢痕的伸长或新着丝粒活性。荧光原位杂交研究表明，5RL缢痕缺乏在谷物着丝粒和新着丝粒中分别存在的两种重复DNA序列CCS1和180bp节结重复序列的可检测量。我们提出，在特殊条件下，如小麦背景中，5RL这个区域通常非着丝粒的DNA获得一种特定的染色质结构，分化为伸长的缢痕，它能够起着丝粒的作用。
