Telomere

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ΕΤΥΜΟΛΟΓΙΑ

Greek telos meaning end and meros meaning part.

A telomere is the genetic segment at the end of a chromosome made up in man of (TTAGGG)n DNA repeats. Small amounts of these terminal sequences are lost in each S phase because of incomplete DNA replication although they can be replaced by telomerase reverse transcriptase (TERT) . Telomeres have key functions in:

  • Ageing
    • The mitotic clock
    • Progeria (Werner's syndrome) causes accelerated telomer shortening but further the DNA helicase mutation of progeria causes impaired telomere replication and stability. However this may be secondary rather than primary. Dyskeratosis congenita is associated sometimes with a normal lifespan and is a poor model for those who associate telemore shortening and ageing.
  • Stem cell differentiation - TERT activates stem cells independent of its telomere lengthening function
    • Haematopoietic stem cells
    • Testis
    • Gastrointestinal tract
  • Malignant transformation
    • It is over expression of TERT that allows cells in a malignancy to divide indefinitely, and the general evidence is that this occurs relatively late in the mutation sequence that lead to malignancy.

History

First described by American biologist Hermann Muller in 1930s.

In the 1970s, Jack Szostak noted that DNA introduced artificially into yeast began to degrade. Elizabeth Blackburn, in her studies on the unicellular protozoan Tetrahymena, noted that the end sequences of the organism's DNA ended with repeats of short DNA sequences. Working in collaboration, the two scientists found that addition of these repeated sequences to the ends of the artificial yeast DNA prevented degradation. It was not until the 1980s that Carol Gardner identified telomerase, the enzyme responsible for regeneration of the telomeres. All three shared the 2009 Nobel Prize for Medicine for their work on telomeres.

Diseases

References