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November 06, 2003


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HARVARD GAZETTE ARCHIVES

Szostak
Jack Szostak: '[We] know that a particular clay mineral helps with the assembly of RNA. There certainly would have been lots of environments on early Earth with clay minerals.' (Staff photo Stephanie Mitchell/Harvard News Office)

A role for clay in formation of the first cells

Did life originally spring from clay?

By Alvin Powell
Harvard News Office

Harvard researchers demonstrated how the first living cells may have formed in a series of experiments that indicate that clay can be an important catalyst for life.

While the research is a far cry from proving that humans sprang from clay, as some creation myths assert, it does provide a possible mechanism for explaining how life initially arose from nonliving molecules.

Researchers at the Howard Hughes Medical Institute and Massachusetts General Hospital showed that the presence of clay aids naturally occurring reactions that result in the formation of fatty sacks called vesicles, similar to what scientists expect the first living cells to have looked like.

Further, the clay helps RNA form. The RNA can stick to the clay and move with it into the vesicles. This provides a method for RNA's critical genetic information to move inside a primitive cell.

Harvard Medical School Professor of Genetics Jack Szostak said he and colleagues Martin Hanczyc and Shelly Fujikawa aren't suggesting they've hit on the exact method by which life initially arose. Still, he said, there are exciting parallels, including the fact that the clay aids in the creation of both the vesicles and the genetic material that would be needed to create a primitive cell.

"It's exciting because we know that a particular clay mineral helps with the assembly of RNA," Szostak said. "There certainly would have been lots of environments on early Earth with clay minerals. It's something that forms relatively easily as rocks weather."

Four characteristics of life

Szostak and his colleagues designed a series of experiments that built on previous findings from other researchers that montmorillonite clay aided the creation of RNA. RNA held the earliest cells' genetic information and, thus, would be an essential component in the formation of early life. The research was detailed in the Oct. 24 issue of the journal Science.

The team first examined whether the clay would affect the formation of the fatty sack vesicles, which have been known to form spontaneously from fatty acids after long periods of time. They found the addition of particles of the montmorillonite clay - widely found in nature today - accelerated the vesicle formation by 100 times, with vesicles forming within a minute.

In a second experiment, the team added clay particles bound to RNA molecules to the fatty acid mixture. The result was that vesicles formed that contained both the clay particles and the RNA molecules bound to them.

Then researchers examined whether the fatty sacks would grow, by adding more fatty acid material, they found that existing vesicles absorbed the material and grew in size.

Finally, Szostak and colleagues tried to see if the vesicles could be induced to divide. They forced them through a filter containing pores too small for the vesicles to pass through. They found that the vesicles broke up into smaller, more numerous ones, without losing all of their contents.

Though the experiments illustrate a possible mechanism for primitive cell formation and growth, Szostak said there remain many missing pieces.

"We're not saying that this is a process that actually happened," Szostak said. "There are a lot of missing links in the chain going from small molecules to complex cells."

One of the largest, he said, is where the original material that formed the RNA would have come from. A second missing piece, he said, involves how RNA might have begun replicating itself to pass genetic information on to the next generation.

"I think [the experiments outline] a plausible step, but what we don't know is how to get the components to build RNA that could assemble on the clay," Szostak said. "We also don't know what kind of membrane-forming molecules were around."

Szostak laughed when asked about parallels to creation myths, several of which have deities creating humans out of clay. There's a few billion years and a lot of missing steps between the formation of simple life and the evolution of humans, he said.

"There's nothing crawling out of the test tubes yet," Szostak said.

alvin_powell@harvard.edu

Related stories:

  • Evidence Found for Origin of Genes

  • Creating Life in a Lab: Using the first living thing on Earth as a model







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