Synonym: Programmed cell death
Pronunciation: ah-poh-toh’-sis: Greek, (1) apo- away from and (2) ptosis, a falling or dropping
‘Apoptosis’ has been derived from a Greek word that describes the falling of the leaves from a tree or petals from a flower. This term was coined to differentiate this form of programmed cell death from the accidental cell deaths caused by inflammation or injury (necrosis).
Programmed cell death is an active process, first described in 1972 and usually proceeds by a distinct series of cellular changes known as apoptosis.
Apoptosis is thus the genetically programmed death of cells that is both a natural development process and the body’s means of destroying abnormal or infected cells.
Events of apoptosis:
During apoptosis, firstly, as a result of cleavage between nucleosomes, chromosomal DNA fragmentation occurs.
Following chromatin condensation, the cell shrinks in and breaks up into membrane-enclosed fragments known as apoptotic bodies.
These apoptotic cells and cell fragments are efficiently recognized and phagocytosed by macrophages and the neighbouring cells, and thus, eventually, these cells, which die by apoptosis, are rapidly removed from tissues.
This removal of the apoptotic cells from the tissues is mediated by the expression of certain signals on the cell surface. These signals are generally known as the “eat me” and include phosphatidylserine, which is restricted normally towards the inner leaflet of the plasma membrane. However, during apoptosis, phosphatidylserine becomes expressed on the cell surface, where it is recognized by receptors expressed by phagocytic cells.
Genes involved in apoptosis:
Programmed cell death was innovatively studied during the development of C. elegans, which eventually provided the critical initial insights that led to understanding the molecular mechanism of apoptosis. These pioneering studies conducted in the laboratory of Robert Horvitz helped initially identify three genes that played key roles in regulating and executing apoptosis.
Mutagenesis of C. elegans in the year 1986 helped identify the genes involved in the developmental cell death (ced-3and ced-4). If either ced-3 or ced-4 was inactivated by mutation, the normally programmed cell deaths did not occur.
A third gene known as the ced-9 functioned as a negative regulator of apoptosis. Whenever this gene ced-9 was inactivated by mutation, the cells failed to survive and instead underwent apoptosis, leading to death. Conversely, if this gene was expressed at an abnormally high level, the normally programmed cell deaths failed to occur.
Article by- SAMPRATI PAREKH (MSIWM049)
- The Cell: A Molecular Approach by Geoffrey M. Cooper – 8thEdition
- Cellular and Molecular Immunology by Abul K. Abbas – 7thEdition