Flatworm Flouts Fundamental Rule of Biology: Worm Regenerates Without Centrosome, a Structure Long Thought Necessary for Cell Division

ScienceDaily (Jan. 5, 2012) — Reporting in the journal Science, researchers at the University of California, San Francisco (UCSF) and the Stowers Institute for Medical Research in Kansas City, MO, have discovered that the worm lacks a key cellular structure called a "centrosome," which scientists have considered essential for cell division.

Every animal ever examined, from the mightiest mammals to the lowliest insects, has these centrosomes in their cells.

"This is the first time we've found one that didn't," said Wallace Marshall, PhD, an associate professor in the Department of Biochemistry & Biophysics at UCSF, who led the research.

The fact that flatworms lack these centrosomes calls into question their purpose, Marshall added. "Clearly we have to rethink what centrosomes are actually doing," he said.

The Necessity of Even Division

A central component of all multicellular life is the ability of cells to divide -- and divide evenly. Before a cell divides, it has to assemble two exact copies of its DNA and then make sure that DNA sorts evenly into the two separate halves as they pinch off. Many health problems arise from cells losing this ability.

A hallmark of cancer, for instance, involves abnormalities in this division. Tumor cells often duplicate extra pieces of DNA. Certain forms of childhood mental retardation are also marked by abnormal divisions, which cause the loss of large pieces of DNA, leading to development problems in certain brain structures.

Centrosomes have been seen as animals' ultimate evolutionary fix for this problem. Plants and fungi don't have them, but animals have had centrosomes in their cells, as long as there have been animals. These structures were thought to play a central role in cell division -- laying down track-like spindles onto which the cells sort their dividing DNA. Centrosomes were seen as so important to cell division that all animals were assumed to have them.

The discovery that at least one animal doesn't came quite unexpectedly.

Interested in the basic mechanics of the centrosome, Marshall and UCSF postdoctoral researcher Juliette Azimzadeh, PhD, teamed up with Alejandro Sánchez Alvarado, PhD, a Howard Hughes Medical Institute and Stowers Institute investigator, who has worked with the flatworm Schmidtea mediterranea for several years.

Read more at: http://www.sciencedaily.com/releases/2012/01/120105174220.htm