Schubert Veit, Kim Young-Min, Berr Alexandre, Fuchs Jörg, Meister Armin, Marschner Sylvia, Schubert Ingo
Leibniz Institute of Plant Genetics and Crop Plant Research (IPK), Corrensstrasse 3, Gatersleben, Germany.
Mol Genet Genomics. 2007 Aug;278(2):167-76. doi: 10.1007/s00438-007-0242-0. Epub 2007 May 24.
The chromosome arrangement in interphase nuclei is of growing interest, e.g., the spatial vicinity of homologous sequences is decisive for efficient repair of DNA damage by homologous recombination, and close alignment of sister chromatids is considered as a prerequisite for their bipolar orientation and subsequent segregation during nuclear division. To study the degree of homologous pairing and of sister chromatid alignment in plants, we applied fluorescent in situ hybridisation with specific bacterial artificial chromosome inserts to interphase nuclei. Previously we found in Arabidopsis thaliana and in A. lyrata positional homologous pairing at random, and, except for centromere regions, sister chromatids were frequently not aligned. To test whether these features are typical for higher plants or depend on genome size, chromosome organisation and/or phylogenetic affiliation, we investigated distinct individual loci in other species. The positional pairing of these loci was mainly random. The highest frequency of sister alignment (in >93% of homologues) was found for centromeres, some rDNA and a few other high copy loci. Apparently, somatic homologous pairing is not a typical feature of angiosperms, and sister chromatid aligment is not obligatory along chromosome arms. Thus, the high frequency of chromatid exchanges at homologous positions after mutagen treatment needs another explanation than regular somatic pairing of homologues (possibly an active search of damaged sites for homology). For sister chromatid exchanges a continuous sister chromatid alignment is not required. For correct segregation, permanent alignment of sister centromeres is sufficient.
间期细胞核中的染色体排列越来越受到关注，例如，同源序列的空间邻近性对于通过同源重组有效修复DNA损伤至关重要，并且姐妹染色单体的紧密排列被认为是它们在核分裂期间双极定向和随后分离的先决条件。为了研究植物中同源配对和姐妹染色单体排列的程度，我们将与特定细菌人工染色体插入片段的荧光原位杂交应用于间期细胞核。此前我们在拟南芥和琴叶拟南芥中发现随机的位置同源配对，并且除了着丝粒区域外，姐妹染色单体经常未对齐。为了测试这些特征是高等植物的典型特征还是取决于基因组大小、染色体组织和/或系统发育关系，我们研究了其他物种中的不同个体位点。这些位点的位置配对主要是随机的。在着丝粒、一些核糖体DNA和其他一些高拷贝位点中发现了姐妹染色单体对齐的最高频率（在>93%的同源物中）。显然，体细胞同源配对不是被子植物的典型特征，并且姐妹染色单体在染色体臂上的对齐不是必需的。因此，诱变处理后同源位置染色单体交换的高频率需要另一种解释，而不是同源物的常规体细胞配对（可能是对受损位点进行同源性的主动搜索）。对于姐妹染色单体交换，不需要连续的姐妹染色单体对齐。为了正确分离，姐妹着丝粒的永久对齐就足够了。
