Zhong X B, Fransz P F, Wennekes-Eden J, Ramanna M S, van Kammen A, Zabel P, Hans de Jong J
Department of Molecular Biology, Wageningen Agricultural University, The Netherlands.
Plant J. 1998 Feb;13(4):507-17. doi: 10.1046/j.1365-313x.1998.00055.x.
The molecular and cytological organization of the telomeric repeat (TR) and the subtelomeric repeat (TGR1) of tomato were investigated by fluorescence in situ hybridization (FISH) techniques. Hybridization signals on extended DNA fibres, visualized as linear fluorescent arrays representing individual telomeres, unequivocally demonstrated the molecular co-linear arrangement of both repeats. The majority of the telomeres consisted of a TR and a TGR1 region separated by a spacer. Microscopic measurements of the TR and TGR1 signals revealed high variation in length of both repeats, with maximum sizes of 223 and 1330 kb, respectively. A total of 27 different combinations of TR and TGR1 was detected, suggesting that all chromosome ends have their own unique telomere organization. The fluorescent tracks on the extended DNA fibres were subdivided into four classes: (i) TR-spacer-TGR1; (ii) TR-TGR1; (iii) only TR; (iv) only TGR1. FISH to pachytene chromosomes enabled some of the TR/TGR1 groups to be assigned to specific chromosome ends and to interstitial regions. These signals also provided evidence for a reversed order of the TR and TGR1 sites at the native chromosome ends, suggesting a backfolding telomere structure with the TGR1 repeats occupying the most terminal position of the chromosomes. The FISH signals on diakinesis chromosomes revealed that distal euchromatin areas and flanking telomeric heterochromatin remained highly decondensed around the chiasmata in the euchromatic chromosome areas. The rationale for the occurrence and distribution of the TR and TGR1 repeats on the tomato chromosomes are discussed.
通过荧光原位杂交（FISH）技术研究了番茄端粒重复序列（TR）和亚端粒重复序列（TGR1）的分子和细胞学组织。在伸展的DNA纤维上的杂交信号，可视化为代表单个端粒的线性荧光阵列，明确显示了两个重复序列的分子共线性排列。大多数端粒由一个TR和一个被间隔区隔开的TGR1区域组成。对TR和TGR1信号的显微镜测量显示，两个重复序列的长度变化很大，最大尺寸分别为223 kb和1330 kb。共检测到27种不同的TR和TGR1组合，表明所有染色体末端都有其独特的端粒组织。伸展的DNA纤维上的荧光轨迹分为四类：（i）TR-间隔区-TGR1；（ii）TR-TGR1；（iii）仅TR；（iv）仅TGR1。对粗线期染色体进行FISH，可将一些TR/TGR1组分配到特定的染色体末端和间质区域。这些信号还为天然染色体末端TR和TGR1位点的反向顺序提供了证据，表明存在一种回折端粒结构，其中TGR1重复序列占据染色体的最末端位置。终变期染色体上的FISH信号显示，常染色体区域着丝粒周围的远端常染色质区域和侧翼端粒异染色质仍高度解聚。讨论了番茄染色体上TR和TGR1重复序列出现和分布的原理。
