Division of Life Science, Graduate School of Natural Science and Technology, Kanazawa University, Kanazawa, Ishikawa, JP.
Autophagy. 2010 Oct;6(7):901-11. doi: 10.4161/auto.6.7.13287. Epub 2010 Oct 2.
Programmed nuclear death (PND) in Tetrahymena is a unique process during conjugation, in which only the parental macronucleus is degraded and then eliminated from the progeny cytoplasm, but other co-existing nuclei such as new micro- and macronuclei are unaffected. PND through autophagic elimination is expected to be strictly controlled, considering the significant roles in ciliates such as turnover of disused organelles and production of the next generation. Here we demonstrate that PND in Tetrahymena involves peculiar aspects of autophagy, which differ from mammalian or yeast macroautophagy. Drastic change of the parental macronucleus occurs when differentiation of new macronuclei is initiated. Combined use of monodansylcadaverine and a lysosome indicator LysoTracker Red showed that prior to nuclear condensation, the envelope of the parental macronucleus changed its nature as if it is an autophagic membrane, without the accumulation of a pre-autophagosomal structure from the cytoplasm. Subsequently, lysosomes approached only to the parental macronucleus and localized at the envelope until a final resorption stage. In addition, we found that the parental macronucleus exhibits certain sugars and phosphatidylserine on the envelope, which are possible "attack me" signals, that are not found on other types of nuclei. These findings suggest that PND is a highly elaborated process, different from the typical macroautophagy seen in other systems, and is executed through interaction between specific molecular signals on the parental macronuclear envelope and autophagic/lysosomal machineries.
四膜虫中的程序性核死亡（PND）是一种在接合过程中特有的现象，在此过程中，只有亲代大核被降解并从子代细胞质中消除，而其他共存的核，如新的小核和大核，不受影响。考虑到在纤毛虫中，如废弃细胞器的更新和下一代的产生等方面的重要作用，PND 通过自噬消除预计将受到严格控制。在这里，我们证明了四膜虫中的 PND 涉及自噬的特殊方面，与哺乳动物或酵母巨自噬不同。当新大核分化开始时，亲代大核会发生剧烈变化。使用单丹磺酰尸胺和溶酶体指示剂 LysoTracker Red 的联合使用表明，在核浓缩之前，亲代大核的包膜会发生变化，就好像它是自噬膜一样，而不是从细胞质中积累前自噬体结构。随后，溶酶体仅接近亲代大核，并定位于包膜上，直到最终吸收阶段。此外，我们发现亲代大核的包膜上存在某些糖和磷脂酰丝氨酸，这些可能是“攻击我”的信号，而其他类型的核则没有这些信号。这些发现表明，PND 是一个高度复杂的过程，与其他系统中典型的巨自噬不同，是通过亲代大核包膜上的特定分子信号与自噬/溶酶体机制之间的相互作用来执行的。
