What Is Programmed Cell Death?

Before the term apoptosis appeared, embryologists have observed the phenomenon of programmed cell death (PCD) in animal development. In recent years, PCD and apoptosis have been used as synonyms, but both There are differences in essence. First, PCD is a functional concept, describing that in a multicellular organism, the death of certain cells is a predetermined and strictly controlled normal component of individual development, and apoptosis is a morphological concept. Cell necrosis is a different form of genetically controlled cell death; secondly, the final result of PCD is apoptosis, but not all apoptosis is programmed.

Programmed cell death

Programmed cell death is a ubiquitous process in the development of organisms, and is an actively and orderly way of cell death that is determined by genes. Specifically refers to cells encountering inside and outside

Although it has been observed in cells as early as 170 years ago

The main characteristics of apoptotic cells are (see Table 15-2):

Most of the research data on the role of PCD and its regulatory mechanisms mainly come from three model systems: nematodes,

PCD is a basic biological phenomenon of cells.

From

If there is a problem with the gene that regulates the cell's "suicide", the dead cell does not die, but continues to divide and multiply, which will cause a problem or evil

Left, normal thymocytes; right, apoptotic thymocytes

Sexual cells grow uncontrollably, such as cancer; if a gene wrongly issues a "suicide order" to a cell that shouldn't die, prevents it from dividing and multiplying, causing a large number of lymphocytes that shouldn't die, destroying the human tissue or immune system , Such as AIDS.

There are two types of genes that control "programmed cell death": one is to inhibit cell death; the other is to initiate or promote cell death. Two types of genes interact to control normal cell death. If all the regulatory genes can be found, their functions analyzed, and drugs that can exert or inhibit these gene functions be developed, then humans can ring the death knell of cancer and AIDS.

Caenorhabditis elegans is an ideal material for studying individual development and programmed cell death. Its life cycle is short and the number of cells is small. If the mature adult is hermaphrodite, there are 959 individual cells and about 2,000 germ cells. In the case of males, there are 1031 individual cells and about 1,000 germ cells. The nervous system consists of 302 cells from 407 precursor cells, and 105 of these precursor cells have undergone programmed cell death.

A research group led by Robert Horvitz of the Massachusetts Institute of Technology has adopted a method of somatic mutation to find a total of 14 genes that play a role in the apoptosis of C. elegans . Among them, three have a role in the implementation of apoptosis: Ced -3, Ced-4 and Ced-9. Among them, the role of Ced-3 and Ced-4 is to induce apoptosis. No apoptosis occurs in mutants lacking Ced-3 and Ced-4, and there are extra cells. Ced-9 inhibits the effects of Ced-3 and Ced-4 and prevents apoptosis from occurring. Insufficient Ced-9 function causes embryos to die due to excessive apoptosis.

Of course, this process requires a lot of hard work, because nematodes have only 959 cells, while the human body has about 1,000 trillion cells.

Winner of the 2002 Nobel Prize in Physiology and Medicine

2002 Nobel: Sydney Brenner, Robert Horwitz and John Sulston used nematodes as biological research objects, and arranged the nematode gene map-the first animal gene map, and found that it can be used for every cell Cell map traced by the division and differentiation process, pointing out that cells undergo a "programmed cell death" process during differentiation, and confirmed the changes in control genes during the "programmed cell death" process. It was found that nematodes control cell death. Key genes, and depicting these gene characteristics, revealing how these genes interact during cell death, and confirming that there are corresponding genes in the human body, this opens the door to explore the differentiation and evolution of human cells. For this, the three scientists won the 2002 Nobel Prize in Physiology or Medicine.