"LUCA" -Search for the Common Ancestor of All Life

Trying identify the "beginning" of life seems an impossible task. 

Just as linguists have been able to establish that all human languages have a common origin, so it turns out that all cellular life has a common origin. The ancestor of all life on Earth today has been dubbed LUCA, short for Last Universal Common Ancestor. The fact that there must have been a LUCA was first made clear in the 1960s when the genetic code was deciphered and found to be universal. In the forty years since the code was cracked, the emphasis is now on trying to reconstruct LUCA, but the emerging picture is substantially blurred by new insights into the evolutionary history of life.

But an evolutionary geneticist from the Université de Montréal, together with researchers from the French cities of Lyon and Montpellier, published a ground-breaking study that characterizes the common ancestor of all life on earth, LUCA (last common ancestor).

The study changes ideas of early life on Earth. "It is generally believed that LUCA was a heat-loving or hyperthermophilic organism. A bit like one of those weird organisms living in the hot vents along the continental ridges deep in the oceans today (above 90 degrees Celsius)," says Nicolas Lartillot, the study's co-author and a bio-informatics professor at the Université de Montréal. "However, our data suggests that LUCA was actually sensitive to warmer temperatures and lived in a climate below 50 degrees."

The research team compared genetic information from modern organisms to characterize the ancient ancestor of all life on earth. "Our research is much like studying the etymology of modern languages so as to reveal fundamental things about their evolution," says professor Lartillot. "We identified common genetic traits between animals, plant, bacteria, and used them to create a tree of life with branches representing separate species. These all stemmed from the same trunk – LUCA, the genetic makeup that we then further characterized."

The group's findings are an important step towards reconciling conflicting ideas about LUCA. In particular, they are much more compatible with the theory of an early RNA world, where early life on Earth was composed of ribonucleic acid (RNA), rather than deoxyribonucleic acid (DNA).

However, RNA is particularly sensitive to heat and is unlikely to be stable in the hot temperatures of the early Earth. The data of Dr. Lartillot with his collaborators indicate that LUCA found a cooler micro-climate to develop, which helps resolve this paradox and shows that environmental micro domains played a critical role in the development of life on Earth.

"It is only in a subsequent step that LUCA's descendants discovered the more thermostable DNA molecule, which they independently acquired (presumably from viruses), and used to replace the old and fragile RNA vehicle. This invention allowed them to move away from the small cool microclimate, evolved and diversify into a variety of sophisticated organisms that could tolerate heat," adds Dr. Lartillot.

Posted by Casey Kazan.

Adapted from materials provided by University of Montreal.

Comments

[EvilCosmicMonkeyfrom Knoxville]

Life solely from RNA ? wouldn't that be a little asymmetrical ? That plus the fact that RNA apparently falls apart in high temperatures would make that argument fall apart as well.

Maybe it would happen on some other planet.