Pyknosis, or karyopyknosis, is the irreversible condensation of chromatin in the nucleus of a cell undergoing necrosis[1] or apoptosis.
[4] Necrosis is a form of regulated cell death due to toxins, infections, and other acute stressors.
[4] These stressors cause swelling/shape modification of cellular organelles leading to the eventual loss of stability and integrity of the cell membrane.
[4] In simpler terms, pyknosis is the process of nuclear shrinkage that may occur during both necrosis and apoptosis.
[5] Karyorrhexis is the fragmentation of a pyknotic cell’s nucleus and the cleavage and condensing of chromatin.
[4] This cleavage, in turn, results in a disruption of the interior of the membrane, which is an initiating factor for chromatin condensation (the second event of nucleolytic pyknosis).
This is due to the fact that caspase-3 cleaves Acinus, which has DNA/RNA binding domains and ATPase activity to initiate the condensation of chromatin.
[4] One protein that plays a significant role in necrotic pyknosis is the barrier-to-autointegration factor (BAF).
This disruption, in turn, may prompt the improper destruction or removal of a cell with damaged elements as well as other related issues.
[8] During apoptosis, DNA fragmentation exposes numerous 3’OH ends, that are labeled with modified deoxy-uridine triphosphate (dUTP) by the TUNEL reaction.
The caspase cascade directly activates caspase-activated DNase (CAD) which initiates DNA fragmentation into smaller pieces resulting in chromatin condensation.
The biochemical techniques used to detect caspase activity include ELISA and fluorometric and colorimetric assays.