Present address: Department of Genetics and Developmental Biology, University of Connecticut Health Center, Farmington, CT 06030, USA.
Present address: Internal Medicine Residency Program, University of Connecticut Health Center, Farmington, CT 06030, USA.
Biol Open. 2014 Apr 11;3(5):353-61. doi: 10.1242/bio.20147708.
One of the most dramatic examples of nuclear morphogenesis occurs during conjugation in Tetrahymena when the micronucleus elongates to a size longer than the cell itself. After contraction to a spherical shape, the nucleus moves directly to chromosome separation in the first meiotic division. Here we investigate the consequences of interrupting the elongation process. Colchicine, a microtubule inhibitor, caused retraction of elongated structures. With time, cells began to lose their micronuclei, and by five hours more than half of the paired cells had at least one cell missing a micronucleus. After reversing the colchicine block, existing micronuclei did not undergo elongation again, nor did meiosis occur. These observations indicate that micronuclear elongation is critical to subsequent meiotic division. Further, nuclear elimination occurs, which could be due to meiotic failure or possibly a problem downstream from meiosis. An analysis of the process of colchicine-induced micronuclear degeneration indicated that it was regulated by a caspase-dependent mechanism, characteristic of apoptosis, and then resorbed by a lysosome-dependent autophagic mechanism. Amicronucleate cells failed to grow when returned to nutrient medium, likely because of a lesion in the post-conjugation reconstruction of a functioning oral apparatus. The ease by which a large number of nuclei are induced to "self-destruct" may make this system useful in investigating the link between colchicine treatment and nuclear death in Tetrahymena, and in investigating how nuclear death could be regulated in living cells more generally. Finally, we note that this phenomenon might relate to the evolution of amicronucleate species of Tetrahymena.
核形态发生最显著的例子之一发生在四膜虫的接合过程中，此时小核伸长到超过细胞本身的长度。收缩成球形后，核直接移动到第一次减数分裂中的染色体分离。在这里，我们研究了中断伸长过程的后果。秋水仙碱是一种微管抑制剂，导致伸长结构回缩。随着时间的推移，细胞开始失去它们的小核，五个小时后，超过一半的配对细胞至少有一个细胞失去了小核。在逆转秋水仙碱阻断后，现有的小核不再伸长，也没有发生减数分裂。这些观察结果表明，小核伸长对随后的减数分裂至关重要。此外，核消除发生，这可能是由于减数分裂失败或可能是减数分裂后下游的问题。对秋水仙碱诱导的小核退化过程的分析表明，它受到半胱天冬酶依赖性机制的调节，这是凋亡的特征，然后通过溶酶体依赖性自噬机制被吸收。当返回营养培养基时，无小核的细胞无法生长，可能是因为在接合后重建功能口器时出现了损伤。大量核被诱导“自我毁灭”的容易程度可能使该系统在研究秋水仙碱处理与四膜虫核死亡之间的联系以及更普遍地研究如何调节核死亡方面非常有用。最后，我们注意到这种现象可能与四膜虫无小核物种的进化有关。
