Pyknosis

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.

Apoptosis
Morphological characteristics of pyknosis and other forms of nuclear destruction
Original caption: [ 7 ] Histopathological findings of the resected left adrenal gland (September 2009). a Gross appearance of the cut surface of the left adrenal tumor 3 cm in size showed the inferior surface to be necrotic. b−i Microscopic examination of the left adrenal tumor (b, d−f; hematoxylin and eosin staining. c, g−i; chromogranin A staining). Nontumoral adrenal gland in the right lower corner, and well-encapsulated tumor in the remainder of the photograph (b). The tumor had a large area of coagulative necrosis in the center. The necrotic material contained morphologically ghost cells (d, e) and was immunohistochemically markedly positive for chromogranin A (c, g, h). There were numerous hemosiderin-laden macrophages and histiocytes accompanied by vascular proliferation in the region adjacent to the area of necrosis (e, h). The viable region along the periphery of the tumor contained numerous cells undergoing pyknosis (f), and the cytoplasm of the tumor cells was positive for chromogranin A staining (i) [ 7 ]
Apoptotic DNA laddering visualized in agarose gel . DNA from cells treated with an apoptotic inducing substance (left). A 1 kb marker (middle). Untreated cell DNA (right)