Freshwater flatworm is 1st animal sans centrosome
Washington: A tiny, freshwater flatworm found in ponds and rivers around the world is the first animal ever discovered without a crucial structure inside its cells known as the centrosome, according to a new study.
The new study by scientists at the University of California, San Francisco (UCSF) and Stowers Institute shows that Schmidtea mediterranea, which lives in southern Europe and Northern Africa, regenerates without centrosome, a structure long thought necessary 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,” Wallace Marshall, the lead researcher, said.
The fact that flatworms lack these centrosomes calls into question their purpose.
“Clearly we have to rethink what centrosomes are actually doing,” he said.
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.
With a charming name that masks an otherwise humble appearance, the Schmidtea mediterranea is a puddle wiggler just a few millimeters long at most. But its remarkable regenerative ability has made it a great scientific curiosity.
When cut into tiny pieces, every piece will grow into a perfectly normal worm in a matter of days. Each offspring can then be segmented over and over again as well — it’s how the worm reproduces.
The original intention of the study was to see what happened to the worm when it lost its centrosome.
Together they manipulated the flatworm to knock out genes needed to assemble these centrosomes. Without centrosomes the worms should have lost their ability to regenerate normally — or so they thought.
They were amazed to find that losing these structures didn’t affect the worms’ ability to regenerate at all. Then they looked more carefully at the worms and discovered that they never had these centrosomes in the first place.
“It came as a surprise to all of us,” Sanchez Alvarado, a Howard Hughes Medical Institute and Stowers Institute investigator, said.
What it means, he said, is that the evolutionary pressure that has maintained these structures in nearly all animals may have very little to do with cell division itself.
“There may be another function for centrosomes that is still obscured,” he added.
The study has been recently published in the journal Science.
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