US scientists have bred a mini-mouse whose cells are two thirds of the normal mouse. It could hold clues as to how cells, organs and animals know when to stop growing, says a report in `Nature` Science update. Jeffrey Settleman and his colleagues of Harvard Medical school were taken aback when their genetically engineered mice produced petite pups only two cm long, compared to the normal three. They found that the pups` cells divided at the normal rate, but were smaller than usual.
The mini-mice suggest that small cells add up to smaller organs and organisms. This may seem obvious - but in fact, small animals do not usually have smaller cells than large animals, they have fewer. Blood cells in a fly and a human are roughly the same size, says the report.
Result such as Settleman`s, however, suggest that at least some of the variation between two organs or animals could be due to bigger or smaller cells.

"It seems you can change animal size by changing cell size", says Sally Leevers, who studies growth regulation at Cancer Research UK in London.

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Excessively large cells may lead to cancer, according to Morris Birnbaum University of Pennsylvania, Philadelphia.

Mini-mouse is the first animal reported with the `small-cell` phenomenon. In the past few years scientists have discovered a group of genes that regulate cell size in other organisms. Bureau Report