Here was one possible way in which the pieces of the RNA world might have come together in cells that could grow and divide. The researchers haven’t actually created synthetic life, but they may be within striking distance. “We have a pretty clear picture of what we have to do, and none of those steps look impossible,” says Szostak.
Courtesy of Martin Hanczyc |
CLAYMATION CELLS For laboratory scientists trying to re-create the primordial ancestor of all life on Earth, the challenge is to combine nucleotides, fatty acids, and water in an actual cell. This is a two-step process. Nucleotides must link together to form RNA strands, and then the RNA must be housed inside a fatty- acid membrane. Szostak and his colleagues were surprised to discover that a ubiquitous clay known as montmorillonite accomplishes both these tasks. When added to the molecular mix, the montmorillonite causes the nucleotides to spontaneously assemble themselves into RNA, which is then trapped inside fatty-acid bubbles called vesicles. The result is something that resembles a cell: It has genetic material and water contained within a waterproof fatty-acid pouch that, under the proper circumstances, could grow and even divide. An image of these makeshift cells (above), taken with an optical microscope and enhanced using fluorescent dye, reveals yellow bits of RNA inside spherical green vesicles. |
Watching the evolution of RNA-based organisms could tell scientists how life got its start on Earth. At the same time, it could alter the way scientists look for life on other planets and moons. The current strategy of astrobiologists is to look for signs of DNA-based life. That’s logical because DNA-based life is the only sort we know actually exists and the only sort scientists can study. But just because DNA-based life is the only sort on Earth today doesn’t mean it’s the only kind in the universe. Creating RNA-based life would show that alternatives are possible. “Once there’s one example of a lab system that’s evolving by itself, then the challenge is to build systems that can evolve under different conditions,” says Szostak. “Could we design cells that grow in environments without water?” Beyond Earth, liquid water seems to be rare. The most common liquid in the solar system is high-pressure liquid hydrogen in the giant gaseous planets Jupiter and Saturn. Could life exist there as well?
As Szostak and other scientists move closer to making new life, they inspire a lot of hand-wringing. Ethicists, philosophers, and theologians have weighed in. Environmentalists have warned of a Pandora’s box waiting to be opened. When asked about these issues, Szostak—understated as always—blinks his eyes slowly and gives a slight shrug. “This thing will basically have no biochemistry,” he says. “It won’t be able to live outside the lab.”
Nonetheless, Szostak suggests that the discoveries made by his research team could someday become a source of new kinds of biotechnology. There are already some companies dedicated to bringing ribozymes from the laboratory to the commercial world, with potential applications as sensitive sensors of biowarfare germs or as medical diagnostic tests. Other ribozymes have shown promise in fighting cancer, heart disease, and HIV. RNA organisms could evolve new ribozymes as well and also produce them in bulk as they multiplied. “Here we have a simple replicating nanosystem,” says Szostak. “Why not direct it to do useful things?”
That prospect lends a profound irony to Szostak’s quest. In trying to re-create the oldest life on Earth, he may end up spawning something entirely new. “There will probably be things to do with this system that we can’t even think of yet,” he says.
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