June 7, 2013
Relatively ‘New’ Genes Can Quickly Become Essential To Life
Brett Smith for redOrbit.com - Your Universe Online
Some genes within an organism´s DNA have been there for a billion years and can be traced back through earlier species, while other genes are newly acquired and only a few million years old.
"The majority of these genes are not going to acquire essential functions" said study co-author Barbara Mellone, and assistant professor of molecular and cell biology at the University of Connecticut. "But the interaction network is completely rewired for this gene."
Along with colleagues at the University of Washington, the Fred Hutchinson Cancer Research Center in Seattle, and the University of Munich, Mellone was able to trace the evolutionary steps of this particular gene from geneticists´ most beloved fruit fly, Drosophila melanogaster. The gene plays a crucial role in splitting up genetic material when cells divide, a process known as chromosome segregation.
"The genus Drosophila offers an unprecedented system in which to study gene evolution because of the detailed evolutionary and genomic data available," Mellone said. "Learning about how new genes acquire new functions is crucial to understanding how whole genomes undergo functional innovation, which is what is needed for new traits to appear in populations that natural selection can act upon."
The gene under scrutiny, which researchers have dubbed Umbrea, is known to play a role in making chromosome segregation happen correctly. While the gene is present in other species of fruit fly, it is not essential in all of them.
To understand how this works, the researchers conducted a sequencing analysis and recorded video of fruit fly cells without Umbrea dividing under a microscope. They found that Umbrea was lost in some of the species, but in Drosophila melanogaster, cells without it failed to separate chromosomes properly and were unable to survive, thus verifying its crucial role in species propagation.
They also found that several stepwise evolutionary changes have led to Umbrea's essentialness. After losing its previous, nonessential function, the protein signaling network was completely rewired, resulting in new sections of code that allowed it to relocate to the centromere, a crucial structure during cell division.
"This gene emerged and wasn't going either way, toward or away from essential function," Mellone said. "Then something happened elsewhere to help make it essential."
The researchers said their findings support the notion that keeping some non-essential genes around might benefit organisms in the long run. These genes appear to be able to acquire new functions under certain conditions.
"Centromere proteins experience rapid evolution in many organisms, including humans, in a constant 'arms race' that exists to maintain the equal segregation of genetic traits," Mellone said.
The scientists suggested that this could shift the way scientists look at other biological processes that may call for genetic innovation to adjust to new challenges.