Ananova:

A "fat switch" which determines whether cells turn into muscle or flab has been discovered by scientists.

In the "on" position it stops precursor cells developing into fat. But when it is switched off even would-be muscle cells change direction and turn into fat instead.

Although the process has been seen in mouse cells, the family of proteins to which the switch belongs is found in all animals. The American scientists say that, while the discovery may not cure obesity in the near future, it opens up new avenues for designing anti-obesity drugs.

The "switch" is a signalling protein called Wnt-10b. Scientists already knew that Wnts, or "wints," regulate complex genetic and biochemical changes during embryonic development. But the new study is the first to identify their role in fat formation.

The research team from the University of Michigan Medical School in Ann Arbor worked with two types of mouse cell - precursor muscle cells called myoblasts and precursor fat cells called preadipocytes. Precursor cells are partially programmed unformed cells which are capable of developing into a limited number of cell types.

Working in the laboratory, the scientists found that in the absence of Wnt-10b both types of mouse precursor cell turned into fat. When the switch molecule was present the myoblasts differentiated into muscle cells.

However, interrupting the Wnt signal caused myoblasts already on their way to becoming muscle cells to switch gear and develop into fat.

Doctoral student Sarah Ross, first author of the research, published in the journal Science, said: "Wnt signalling functions as a fat switch.

"When it's on, fat cell formation is repressed. When it's off, fat is initiated. Without this signal, muscle cell precursors can even be reprogrammed to undergo adipogenesis (fat formation) so that they turn into fat."

Prof Ormond MacDougald, who directed the study, now plans to study whether Wnt-10b has the same fat-inhibiting effect in living mice as it does in laboratory cultures of mouse cells. He hopes to alter production of Wnt-10b with genetic engineering to create a "fat free mouse".