To prevent cells from losing some of their genetic material during division, telomere repeats have the ability to restore their length. This is the essence of the “end replication” process. But scientists did not immediately understand how the end sequences are built up. Several different models were proposed. Russian scientist A.M. Olovnikov suggested the existence of a special enzyme (telomerase) that builds up telomere repeats and thereby maintains the telomere length constant.

In the mid-1980s Carol Greider came to work in Blackburn’s laboratory and it was she who discovered that telomere repeats were attached to synthetic telomere-like “seed” in infusoria cell extracts. Apparently, the extract contained some protein that promoted telomere buildup. Thus, Olovnikov’s conjecture was brilliantly confirmed and the telomerase enzyme was discovered. In addition, Greider and Blackburn determined that telomerase consists of a protein molecule that actually carries out telomere synthesis and an RNA molecule that serves as a matrix for their synthesis.

WITHOUT TELOMERASE THE CELL AGES, BUT WITH TELOMERASE IT IS REBORN.

Later, Shostak’s lab discovered that certain mutations in certain yeast genes lead to a rapid shortening of telomeres after each cell division cycle, causing chromosomes to become unstable and cells to go into senescence (senescence). We now know that these genes encode telomerase. The data obtained confirmed another hypothesis of A.M. Olovnikov that the loss of telomere repeat length in each round of chromosome replication depends on the number of cell divisions.

Thus, telomerase solves the “end replication” problem: it synthesizes repeats and maintains telomere length. In the absence of telomerase, with each cell division telomeres become shorter and shorter, and at some point the telomere complex is destroyed, signaling programmed cell death. That is, the length of telomeres determines how many divisions the cell can complete before its natural death.

In fact, different cells may have different lifespans. In embryonic stem cell lines, telomerase is very active, so telomere length is kept constant. This is why embryonic cells are “forever young” and capable of unlimited reproduction. In normal stem cells, telomerase activity is lower, so telomere shortening is only partially compensated. In somatic cells, telomerase does not work at all, so telomeres shorten with each cell cycle. Telomere shortening leads to the Heiflick limit – the transition of cells to the sessence state. This is followed by mass cell death. The surviving cells are reborn as cancer cells (as a rule, telomerase is involved in this process). Cancer cells are capable of unlimited division and maintenance of telomere length.

The presence of telomerase activity in those somatic cells where it is not normally present can be a marker of malignancy and an indicator of an unfavorable prognosis. For example, if telomerase activity appears at the very beginning of lymphogranulematosis, we can talk about oncology. In cervical cancer, telomerase is already active at the first stage.

Mutations in the genes encoding components of telomerase or other proteins involved in telomere length maintenance cause hereditary hypoplastic anemia (hematopoiesis associated with bone marrow depletion) and congenital X-linked dyskeratosis (a severe hereditary disease accompanied by mental retardation, deafness, irregular development of tear ducts, nail dystrophy, various skin defects, tumor development, immune disorders, etc.).