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Sea shells and blood cells

Crystal-carrying blood cells actively participate in oyster shell formation. In this electron micrograph, these special blood cells (green) interact with crystal structures (gold) at the site of shell formation. The blood cells (green) deposit microscopic calcium carbonate crystals that seem to become part of the shell. Image Science.
Click here for a high resolution photograph.

While stepping on a sharp shell may draw blood, new research links sea shells and blood cells in a totally different way.

Scientists know that oysters make their shells from crystals but where the crystals are made is still a mystery. A new study in the 09 April 2004 issue of the journal Science suggests that these shell-building crystals are formed in a special class of blood cells that travel to the site of shell formation and unload their crystal cargo.

These crystal-carrying cells "look like diamonds that are crawling around," according to study author Andrew Mount from Clemson University in Clemson, South Carolina.

To study the process of shell building, the scientists cut notches in oyster shells. These cuts did not hurt the oysters, just as cutting your hair doesn't hurt you. When the oysters rebuilt their shells, the number of blood cells with crystals jumped in relation to similar cells without crystals.

Eastern Oyster C. virginica at 48 hours after induction. The arrow points to new shell that has regenerated within the cut or notched region of the mollusk. Image Science.
Click here for a high resolution photograph.

The scientists first observed the crystals inside blood cells using the kinds of microscopes you might find in a high school biology laboratory.

"We kept following our noses," Mount explained. They looked more closely at the intriguing blood cells with powerful microscopes that use electron beams and X-rays to magnify their specimens.

Understanding the blood-shell connection might be useful for people who grow cultured pearls in oysters, Mount said.

To culture pearls, scientists insert a pearl "seed" and a bit of tissue from a different oyster into the pearl-growing oyster's flesh. The pearl forms around this seed as the oyster adds layer after layer of a protective coating made of crystals. This protective coating, called "nacre," gives pearls their shimmer and glow.

Mount thinks that the crystal-carrying blood cells might be involved in both shell building and pearl development.


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