Necrotic pyknosis is a morphologically and biochemically distinct event from apoptotic pyknosis

Abstract

Classification of apoptosis and necrosis by morphological difference has been widely used for decades. However, this method has been seriously doubt in recent years, mainly due to lack of functional and biochemical evidence to interpret the morphology changes. To address these questions, we devised genetic manipulations in Drosophila to study pyknosis, a process of nuclear shrinkage and chromatin condensation occurred in apoptosis and necrosis. By following the progression of necrotic pyknosis, we surprisingly observed a transient state of chromatin detachment from the nuclear envelope (NE), followed with the NE completely collapsed onto chromatin. This phenomenon leads us to discover that phosphorylation of barrier-to-autointegration factor (BAF) mediates this initial separation of NE from chromatin. Functionally, inhibition of BAF phosphorylation suppressed the necrosis in both Drosophila and human cells, suggesting necrotic pyknosis is conserved in the propagation of necrosis. In contrast, apoptotic pyknosis did not show a detached state of chromatin from NE and inhibition of BAF phosphorylation had no effect on apoptotic pyknosis and apoptosis. Our research provides the first genetic evidence supporting morphological classification of apoptosis and necrosis by pyknosis.