What is the Difference Between Pyknosis Karyolysis and Karyorrhexis

The main difference between pyknosis, karyolysis, and karyorrhexis is that pyknosis is the irreversible condensation of chromatin, karyolysis is the nuclear fading, whereas karyorrhexis is nuclear fragmentation. 

Pyknosis, karyolysis, and karyorrhexis are three processes that occur in cells undergoing necrosis or apoptosis. 

Key Areas Covered

1. What are Pyknosis
– Definition, Features, Importance
2. What are Karyolysis
– Definition, Features, Importance
3. What are Karyorrhexis
– Definition, Anatomy, Importance
4. Similarities Between Pyknosis Karyolysis and Karyorrhexis
– Outline of Common Features
4. Difference Between Pyknosis Karyolysis and Karyorrhexis
– Comparison of Key Differences

Key Terms  

Karyolysis, Karyorrhexis, Pyknosis

What is Pyknosis

Pyknosis is the irreversible condensation of chromatin and the nucleus that commonly occurs in both apoptotic and necrotic cell death. The nucleus undergoes condensation, chromatin marginalization, and fragmentation, which occur in apoptosis. Here, chromatin undergoes condensation into a few large, regular chromatin clumps. These chromatin clumps are eventually packed into apoptotic bodies. In contrast, nuclei of necrotic cells condense into small chromatin clumps. They show irregular and dispersed morphologies, and they undergo dissolution later. Therefore, two types of pyknosis occur depending on the type of cell death. Importantly, pyknosis is a cell death marker both in vitro and in vivo.

Figure 1: Apoptosis

Furthermore, pyknosis is always followed by karyorrhexis, which is the fragmentation of the nucleus. Apart from cell death, it also occurs in the maturation of red blood cells and neutrophils. In the metarubricyte stage, red blood cells undergo condensation of the nucleus before expelling it. In neutrophils, the nucleus condenses into several connected lobes. 

What is Karyolysis

Karyolysis is the complete dissolution of nuclear components that occur in cell death. It occurs due to the enzymatic degradation by endonucleases. DNase γ is an example of such endonuclease that causes the fragmentation of the nucleus. It is a secreting protein of the DNase I family. Karyolysis follows karyorrhexis.

Figure 2: Pyknosis, Karyolysis, and Karyorrhexis

Moreover, the whole cell stains uniformly with eosin after karyolysis. Also, karyorrhexis results in the dissolving of apoptotic bodies. Cells undergo pyknosis and karyolysis of the nuclei and disintegrate the nucleus in urine. Malignant cells in urine also show these characteristics. 

What is Karyorrhexis 

Karyorrhexis is the destructive fragmentation of the nucleus of a dying cell. It results in the distribution of chromatin through the cytoplasm in an irregular way. Also, it occurs after pyknosis. Importantly, it occurs due to programmed cell death, necrosis, or cellular senescence.  

Further, apoptosis is a process of programmed cell death (PCD), which consists of a sequence of events leading to the cell’s death. Generally, it plays a key role in the development of the organism. It is also important for the normal process of cell ageing. Therefore, it is a part of the regular physiological activity of many healthy tissues of multicellular organisms. 

Similarities Between Pyknosis Karyolysis and Karyorrhexis

• Pyknosis, karyolysis, and karyorrhexis are three processes in cells undergoing necrosis and apoptosis.
• They are morphological changes that occur in the dying cells.

Difference Between Pyknosis Karyolysis and Karyorrhexis

Definition

Pyknosis refers to a degenerative condition of a cell nucleus marked by clumping of chromosomes, hyperchromatism, and shrinking of the nucleus. In contrast, karyolysis refers to the complete dissolution of the chromatin of a dying cell due to the enzymatic degradation by endonucleases. Meanwhile, karyorrhexis refers to a degenerative cellular process involving fragmentation of the nucleus and the breakup of the chromatin into unstructured granules.  

Importance

Pyknosis is the irreversible condensation of chromatin; karyolysis is the nuclear fading, and karyorrhexis is nuclear fragmentation. 

Karyorrhexis 

Pyknosis and karyolysis follow karyorrhexis, while karyorrhexis is the fragmentation of the nucleus. 

Conclusion

In brief, pyknosis, karyolysis, and karyorrhexis are three processes that occur in necrosis and apoptosis cells. Pyknosis is the irreversible condensation of chromatin. Also, karyolysis is the nuclear fading. Both pyknosis and karyolysis follow karyorrhexis, which is the fragmentation of the nucleus. Therefore, the main difference between pyknosis, karyolysis, and karyorrhexis is their effect on the cell nucleus. 

References:

1. Hou, L., Liu, K., Li, Y., Ma, S., Ji, X., & Liu, L. (2016, August 15). Necrotic pyknosis is a morphologically and biochemically distinct event from apoptotic pyknosis. The Company of Biologists. 
2. Takada S, Watanabe T, Mizuta R. DNase γ-dependent DNA fragmentation causes karyolysis in necrotic hepatocyte. J Vet Med Sci. 2020 Jan 10;82(1):23-26. doi: 10.1292/jvms.19-0499. Epub 2019 Nov 18. PMID: 31735730; PMCID: PMC6983664.

Image Courtesy:

1. “Apoptosis” By Emma Farmer – Own Work (Public Domain) via Commons Wikimedia
2. “Nuclear changes” By Cartwright – Own work (Public Domain) via Commons Wikimedia