Centrioles - Counter Of Life

Main Category: Biology / Biochemistry
Also Included In: Seniors / Aging
Article Date: 07 Mar 2006 - 22:00 PDT

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The Tbilisi researchers J.B. Tkemaladze (Center for systems analysis of Georgia) and K.N. Chichinadze from the Beritashvili Institute of Physiology, Academy of Sciences of Georgia, believe that centrioles - protein structures that participate in animal cell division - are responsible for age-related changes of cells in a multicellular organism. Animal cells can divide for a strictly defined number of times, after which they inevitably perish, and these are centrioles in particular that, in researchers' opinion, act as a fission counter.

Ageing of the organism is ageing of its cells. It starts when the cell becomes quite differentiated, that is specialized, in the course of a certain number of fissions. Such cell can live very long, neurons, for example, live for several dozens of years, but as time passes, its "capacity for work" decreases, and the cell perishes. Experiments of recent years proved that the number of divisions allowed for the cell does not depend on the length of end sections of its chromosomes, telomer. According to the Georgian researchers' opinion, "ageying factors" should be sought not in genome nor even in the cellular nucleus, otherwise scientists would not have succeeded to grow cloned animals from the body cell's nucleus. Therefore, ageing factors should be contained in cytoplasm, and if we recall that the age of cells is determined not by the time but by the number of cellular divisions, and the division process is directly connected with centrioles, then centrioles in particular are most logical to be considered the clock measuring cellular life.

Centrioles - these are two protein cylinders located side by side, transversely to each other. They redouble before each cellular division. Besides division, centrioles "guide" formation of protein bands and microtubules that constitute the skeleton of a cell or cytoskeleton. According to the recent data, the role of centrioles and cytoskeleton is extremely important in animal cell. It is cytoskeleton that coordinates cell metabolism, initial phases of embyronic growth, cells consolidation into a tissue. Microtubules determine transfer of practically all intracellular components, including those during cellular division. Cytoskeleton conducts external signals into the cellular nucleus, including the command to trigger apoptosis - cell extermination. Most probably, this structure participates in malignant transformation of the cell, in any case, it regulates the work of multiple important oncogenes. And, finally, centrioles may probably control both the telomer length and the telomerase enzyme work.

When the cell stops dividing and specializes, its centrioles deteriorate irreversibly. Only the cells that are capable of restoring this damage, can recover the ability to division. Such are, for example, cells of adult animals' liver, one of a few organs capable of regeneration.

According to Georgian researchers' hypothesis, the cells initially devoid of centrioles and cytoskeleton, or the cells where these structures appeared for the first time, cannot count their divisions and therefore are, firstly, immortal, and secondly, not specialized. These conditions are met by higher plants' cells, fertilized ovum and early blastomeres of some animals. These cells are really immortal and not specialized. If we spoil centrioles of a differentiated cell in some way, it will also acquire immortality. Such are cancerous and transformed cells, where a lot of researchers have discovered drastic change of the cytoskeleton structure and centrioles' orientation. Malignant cells are immortal, and the level of their specialization corresponds to the evolution stage where transformation caught them.

As the Georgian researchers can explain behavior of all types of immortal cells of multicellular organisms, they assume that the centriole model of ageing has the right to exist and sooner of later it will be proved experimentally.

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