Discovery shows worm regenerates without centrosome, a structure long thought necessary for cell division.

Flatworm

A tiny, freshwater flatworm found in ponds and rivers around the world that has long intrigued scientists for its remarkable ability to regenerate has now added a new wrinkle to biology.

Reporting in the journal Science today (Jan. 5), researchers at the University of California, San Francisco, 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, Ph.D., 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.

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Meiosis – the pairing and recombination of chromosomes, followed by segregation of half to each egg or sperm cell – is a major crossroads in all organisms reproducing sexually. Yet, how the cell precisely choreographs these chromosomal interactions is a long-standing question.

New findings by UC Berkeley scientists show that the cell’s cytoskeleton, which moves things around in the cell, plays a critical role, essentially reaching into the nucleus to bring chromosome pairs together in preparation for recombination and segregation.

In fact, the cytoskeleton appears to encourage the dance of the chromosomes around the nuclear membrane as they search for their partners, and help make sure they have the right partner before meiosis continues.

The results are published online today (Nov. 12), and will appear in the Nov. 25 print issue of the journal Cell.

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