减数分裂通过两轮染色体分离减少倍性,然后进行一轮DNA复制。在减数分裂I中,同源染色体在减数分裂II时分离,姐妹染色单体彼此分开。拓扑异构酶II(TopoII)是一种保守的酶,通过引入瞬时双链断裂来改变DNA结构。在有丝分裂期间,TopoII可缓解复制过程中与解链DNA相关的拓扑应力,重组,和姐妹染色单体分离。TopoII还在维持有丝分裂染色体结构中起作用。然而,TopoII在减数分裂过程中的作用和调节尚不明确。以前,我们发现了一个TopoII的等位基因,top-2(it7),在秀丽隐杆线虫精子发生减数分裂I期间破坏同源染色体分离。在基因筛选中,我们在5'-酪氨酰-DNA磷酸二酯酶2(Tdp2,秀丽隐杆线虫tdpt-1)中鉴定了不同的点突变,它们抑制了前2(it7)胚胎致死率。Tdp2去除捕获的Top-2-DNA复合物。tdpt-1抑制突变拯救胚胎致死性,改善染色体分离缺陷,并恢复TOP-2蛋白水平的TOP-2(it7)。这里,我们表明,TOP-2和TDPT-1均在生殖系细胞核中表达,但在减数分裂后期之前占据不同的区室。我们还证明了tdpt-1抑制是由于蛋白质功能的丧失,并且tdpt-1突变在减数分裂中不具有独立于top-2(it7)的表型。最后,我们发现tdpt-1抑制突变会损害磷酸二酯酶的活性,影响TDPT-1的稳定性,或破坏蛋白质相互作用。这表明野生型TDPT-1蛋白在减数分裂期间抑制受损的TOP-2的染色体生物学功能。
Meiosis reduces ploidy through two rounds of chromosome segregation preceded by one round of DNA replication. In meiosis I, homologous chromosomes segregate, while in meiosis II, sister chromatids separate from each other. Topoisomerase II (Topo II) is a conserved enzyme that alters DNA structure by introducing transient double-strand breaks. During mitosis, Topo II relieves topological stress associated with unwinding DNA during replication, recombination, and sister chromatid segregation. Topo II also plays a role in maintaining mitotic chromosome structure. However, the role and regulation of Topo II during meiosis is not well-defined. Previously, we found an allele of Topo II, top-2(it7), disrupts homologous chromosome segregation during meiosis I of Caenorhabditis elegans spermatogenesis. In a genetic screen, we identified different point mutations in 5\'-tyrosyl-DNA phosphodiesterase two (Tdp2, C. elegans tdpt-1) that suppress top-2(it7) embryonic lethality. Tdp2 removes trapped Top-2-DNA complexes. The tdpt-1 suppressing mutations rescue embryonic lethality, ameliorate chromosome segregation defects, and restore TOP-2 protein levels of top-2(it7). Here, we show that both TOP-2 and TDPT-1 are expressed in germ line nuclei but occupy different compartments until late meiotic prophase. We also demonstrate that tdpt-1 suppression is due to loss of function of the protein and that the tdpt-1 mutations do not have a phenotype independent of top-2(it7) in meiosis. Lastly, we found that the tdpt-1 suppressing mutations either impair the phosphodiesterase activity, affect the stability of TDPT-1, or disrupt protein interactions. This suggests that the WT TDPT-1 protein is inhibiting chromosome biological functions of an impaired TOP-2 during meiosis.