News (31)

 

Using modern molecular tools and fieldwork, University of Nebraska-Lincoln biologist Jay Storz and colleagues have demonstrated for the first time that different species can take different genetic paths to develop the same trait. The team's findings appear in the Oct. 21 issue of the journal Science.

 

"There's this really long-standing question in evolutionary genetics about the predictability of genetic change," said Storz, Susan J. Rosowski professor of biological sciences.

 

In other words, did species with a common, beneficial trait undergo the same genetic changes to evolve that trait? Or did the trait develop through different, and therefore unpredictable, genetic paths?

 

It turns out that natural selection, a primary evolutionary process, can dependably produce similar, beneficial traits in different species. But at the molecular level, the evolutionary changes tend to be highly idiosyncratic, and are therefore far less predictable.

 

To find that out, Storz turned to birds living in South America's Andes Mountains. Comparing high-altitude bird species with their lowland counterparts, his team determined that the high-altitude birds had evolved red blood cells with hemoglobin proteins that more readily bind oxygen molecules. This trait benefits species living in low-oxygen settings, such as the mountains.

 

Storz and his team tested the hemoglobin proteins from numerous high-altitude bird species and identified which differences, or mutations, in the proteins' makeup were responsible for the high-altitude trait. In most cases, the change in protein function among the different species was caused by different mutations.

 

"What this indicates is that there are many possible mutations that can all produce the same phenotypic effect (trait)," Storz said. "We can't predict which particular mutations are responsible for these changes." One possible reason for this variability is that during evolution, the hemoglobins of different species have each accumulated their own unique set of mutations. Given these distinct genetic backgrounds, a mutation that produces a beneficial effect in one species may produce a detrimental effect in a different species.

 

To test this theory, Storz's team used genetic engineering tools to reconstruct and resurrect the hemoglobin proteins of several ancestral bird species, including the ancestor common to all birds, which existed more than 100 million years ago. Engineering the high-altitude hemoglobin mutations into the ancient bird proteins resulted in vastly different effects than in contemporary birds.

 

As evolution advances through time, different mutations accumulate in distinct species and settings. Natural selection applies similar pressures for species to adapt as they move to higher altitudes, for example, but the adaptation must take different genetic paths to get there.

 

"This is a new phenomenon that our findings have helped reveal," Storz said. His team continues to explore historical influences on genetic adaptation.

 

Researchers at University of California San Diego School of Medicine have discovered that Zika virus infection leads to modifications of both viral and human genetic material. These modifications — chemical tags known as methyl groups — influence viral replication and the human immune response. The study is published October 20 by Cell Host & Microbe.

 

“I’m excited about this study because it teaches us something new about the human immune system,” said senior author Tariq Rana, PhD, professor of pediatrics at UC San Diego School of Medicine. “But these findings are also something researchers should keep in mind as they are designing new Zika virus vaccines and treatments that target the viral genome — some approaches won’t work unless they take methylation into account.”

 

In human cells, RNA is the genetic material that carries instructions from the DNA in a cell’s nucleus out to the cytoplasm, where molecular machinery uses those instructions to build proteins. Cells can chemically modify RNA to influence protein production. One of these modifications is the addition of methyl groups to adenosine, one of the building blocks that make up RNA. Known as N6-methyladenosine (m6A), this modification is common in humans and other organisms.

 

In contrast to humans, the entire genomes of some viruses, including Zika and HIV, are made up of RNA instead of DNA. These viruses hijack the host’s cellular machinery to translate its RNA to proteins. Rana and his team previously discovered that m6A plays an important role in HIV infection.

 

“After that, we decided to investigate m6A RNA in Zika virus as well, since we didn’t want to miss out on this important information the way we missed it for 30 years of HIV research,” Rana said.

 

When Zika virus infects a human cell, Rana’s team found, the cell modifies viral RNA with m6A as a means to get rid of the infection. RNA tagged with m6A is a beacon for human enzymes that come along and destabilize it. In addition, they found that this host response to Zika viral infection also induced specific m6A modifications on human RNA. These human RNA changes were not present in the absence of Zika virus.

 

To unravel the role of m6A in Zika virus infection of human cells growing in the laboratory, the researchers removed the human enzymes responsible for adding methyl groups to viral RNA. Without m6A, the viral RNA was more stable and viral replication increased, as compared to human cells with normal methylation enzymes. In contrast, silencing the human enzymes that remove methyl groups — increasing m6A methylation, in other words — decreased Zika virus production.

 

Next, Rana and team will investigate the role of RNA modifications in the viral life cycle, and how the human immune response is altered by various Zika virus strains. They are also developing small molecules to target specific RNA structures as a means to treat Zika virus infections.

 

Study co-authors include: Gianluigi Lichinchi, Yinga Wu, UC San Diego and Sanford Burnham Prebys Medical Discovery Institute; Boxuan Simen Zhao, Zhike Lu, Chuan He, University of Chicago and Howard Hughes Medical Institute; and Yue Qin, UC San Diego.

 

This research was funded, in part, by the National Institutes of Health (grants AI43198, AI125103, DA039562) and Howard Hughes Medical Institute.