Death harmony played by nucleus and mitochondria -: Nuclear apoptosis during conjugation of Tetrahymena

Tetrohymena programmed nuclear death or nuclear apoptosis is a unique process during conjugation in which only the parental macronucleus is eliminated from the progeny cytoplasm, and other nuclei such as new micro- and macronuclei are unaffected. The nuclear death process consists of three successive steps: chromatin cleavage into high-molecular mass DNA, oligonucleosomal laddering concomitant with nuclear condensation, and complete degradation of the nuclear DNA. Following the first step of the death process, the parental macronucleus is engulfed by a large autophagosome in which many mitochondria are incorporated. Those sequestered mitochondria simply break down and release endonuclease similar to mammalian endonuclease G that is responsible for the generation of the DNA ladder, leading to the conclusion that mitochondria play a crucial role in the execution of the death program. Thus, the parental macronucleus is subject to final death by autophagy in collaboration with caspase-like enzymes, resulting in the ultimate outcome of nuclear resorption.