Editorial: Marvellous rodent

Published in The Hindu on July 21, 2011

Increase in human life expectancy produces a concomitant increase in the number of harmful mutations and accumulation of different forms of damages, which in turn enhances the risk of cancer and old-age diseases. But the genome of the naked mole-rats (Heterocephalus glaber) sequenced recently may hold the key to reducing the risk of these diseases and perhaps even to preventing them. The genome is expected to have about 20,000 genes (as in the case of other rodents) and nearly three billion base pairs (in line with other mammalian genomes). The four-inch-long rodents that live in burrows in the east African desert have intrigued scientists for a variety of reasons. The foremost among them is their exceptional longevity — exceeding 28 years. To provide a ready measure, a house mouse of the same size has a maximum lifespan of four years. One would expect naked mole-rats to incur the greatest risk of developing cancer owing to this long lifespan but, actually, not a single case of cancer has been seen in them so far. According to a study published in November 2009 in the Proceedings of the National Academy of Sciences (PNAS) journal, the H. glaber species has a unique two-level mechanism that renders it tumour-resistant. Two proteins stop the cells from dividing the moment they make contact with each other. Contact inhibition is a key anti-cancer mechanism. Although humans and mice also produce these proteins, only one of them serves as a checkpoint for stopping cell growth.

However, contact inhibition may not be the only mechanism that protects the tiny rodents from cancer. In an experiment carried out by the PNAS authors, the rodent cells grew to become only small colonies; they never reached the size of a tumour even when contact inhibition was completely eliminated. The online availability of the genome at the ‘Naked Mole-Rat Genome Resource’ (http://www.naked-mole-rat.org/) will prove to be of immense value to scientists in investigating the unknown factors. Short-lived, cancer-prone animals like mice that have fewer anti-cancer adaptations have long been used for cancer research. While mice studies have been useful in finding ways of treating cancer, the arsenals for preventing the disease may come up only by studying animals like the naked mole-rats. The genome sequence should also help scientists investigate how the rodents successfully slow down the damage accumulation process, and thereby delay aging. This marvelous species does not show any age-related changes in body composition, physiology, and molecular function from the age of two to more than 20 years.