Like the bones beneath your skin, the skeleton of a cell gives strength and rigidity to the tiny structures that make up your body.

More important, these "cytoskeleton" structures give the cells their infinitely variable shapes.

And the shape of a cell largely dictates its function.

Understanding the way these cytoskeletons shift their shapes and help cells migrate around the body landed scientists Alan Hall and Dr. Thomas Pollard a pair of prestigious Gairdner Awards for 2006.

"The biggest difference between your skeleton and the skeleton of a cell is that where your skeleton can't change, the skeleton of a cell can change," says Hall, chairman of the cell biology program at New York's Memorial Sloan-Kettering Cancer Center.

"They change in response to (outside) signals that tell that skeleton to rearrange itself and take on a different shape."

Dr. Pollard, a professor of cellular and developmental biology at Yale University, and Hall were both cited for "discoveries related to understanding the cytoskeleton of the cell and the basis of cell mobility and its relevance to human disease."

The process of shifting cell shapes, and their movement around the body, is critical to understanding fetal development and the growth of humans during childhood.

As the body grows, it needs to sprout arm, toe, brain, liver and a myriad of other cell types. And these specialized cells must not only morph into the correct shape, but also migrate to the appropriate part of the body to do so.

This process largely ceases at physical maturity, Hall says, except in the case of cancer.

"This is almost like a reawakening of that program in the cancer cells, inappropriately, of course," says Hall. Malignant cells not only change their shape, but also metastasize.

Hall and Dr. Pollard have led the way in discovering the signalling processes behind the reshaping and migrating properties of cytoskeletons in cancer cells.