The Role of Telomeres in Chromosome Pairing in Meiosis

减数分裂的基本功能是使基因组单倍化，这一过程依赖于减数分裂前期的染色体配对。长期以来的细胞学和遗传学研究表明，端粒运动在减数分裂染色体配对中起到了作用，但几乎没有实验证据表明端粒运动在减数分裂染色体配对中的作用，也没有多少对其中涉及的分子机制的深入了解。在酿酒酵母中，减数分裂端粒蛋白Ndj1p是正常的端粒组织和正常的减数分裂染色体行为所必需的，它的缺乏会导致轴向元件形成、联会和进入第一次减数分裂的延迟，以及染色体重组和分离的缺陷。因此，Ndj1p可能在端粒发挥作用，促进染色体配对，可能是在花束形成的减数分裂早期阶段。Ndj1p通过一起移动染色体和/或通过稳定配对相互作用来促进端粒介导的同源配对的假设将通过使用定量免疫细胞学方法检查固定的嵌入材料中的端粒位置以及分析绿色荧光蛋白标记的染色体在体内的运动来验证。此外，还将使用定量免疫细胞学方法比较野生型和NDJj1缺失细胞中轴向元件的形成、突触和重组，并特别关注这些事件相对于亚核位置的动力学。NdJ1是亚端粒配对所必需的假设，在没有重组的情况下持续存在，将通过使用基于原位杂交的分析评估端粒附近的配对来检验。NDJ1通过影响DNA双链断裂形成来影响重组的假设将通过比较双链断裂的频率和位置以及在不同野生型背景和断裂持续且稳定的突变背景下断裂形成的动力学来进行评估。最后，对可能与NDJ1相互作用的必需基因进行减数分裂和NDJ1特有功能的评估，使用质粒法确定功能分离和/或条件性突变。这些实验提出的问题对于理解减数分裂染色体配对和端粒介导的染色体在核中定位的机制具有普遍意义，端粒介导的染色体定位可以影响任何对核结构敏感的过程，从而影响染色体分离的保真度。

The essential function of meiosis is to haploidize the genome, a process which depends on chromosome pairing in meiotic prophase. A long history of cytological and genetic studies have suggested a role for telomere-mediated movements in meiotic chromosome pairing but there has been little experimental evidence for the role and few insights into the molecular mechanisms involved. The meiotic telomere protein Ndj1p is required for normal telomere organization and for normal meiotic chromosome behavior in S. cerevisiae, its absence causing delays-in axial element formation, synapsis and entry into the first meiotic division-and defects in chromosome recombination and segregation. Thus, Ndj1p may function at telomeres to facilitate chromosome pairing, perhaps at the early meiotic stage of bouquet formation. The hypothesis that Ndj1p fosters telomere-mediated homologous pairing by moving chromosomes together and/or by stabilizing pairing interactions will be tested by examining telomere positions in fixed, embedded material using a quantitative immunocytological approach and also by analyzing the movements of green fluorescent protein-tagged chromosomes in vivo. In addition, axial element formation, synapsis, and recombination will be compared in wild-type and NDJj1 deletion cells using a quantitative immunocytological approach, with particular attention to the kinetics of these events with respect to subnuclear locations. The hypothesis that NdJ1 is required for subtelomeric pairing associations that persist in the absence of recombination will be tested by assessing pairing near the telomeres using an in situ hybridization-based assay. The hypothesis that NDJ1 influences recombination by affecting DNA double-strand break formation will be assessed by comparing the frequency and positions of double-strand breaks and the kinetics of break formation in different wild-type backgrounds and in mutant backgrounds where breaks persist and are stable. Finally, essential genes which are candidates for interaction with NDJ1 will be evaluated for meiosis-and NDJ1-specific function using a plasmid-shuffle approach to identify separation-of-function and /or conditional mutations. The questions addressed by these experiments are of general significance for their importance in understanding mechanisms of meiotic chromosome pairing and of telomere-mediated positioning of chromosomes in the nucleus, which can influence any process sensitive to nuclear architecture, and thus affect the fidelity of chromosome segregation.