A huge chunk of a tardigrade's genome comes from foreign DNA

November 23, 2015

Researchers from the University of North Carolina at Chapel Hill have sequenced the genome of the nearly indestructible tardigrade, the only animal known to survive the extreme environment of outer space, and found something they never expected: that they get a huge chunk of their genome - nearly one-sixth or 17.5 percent - from foreign DNA.

"We had no idea that an animal genome could be composed of so much foreign DNA," said co-author Bob Goldstein, faculty in the biology department in UNC's College of Arts and Sciences. "We knew many animals acquire foreign genes, but we had no idea that it happens to this degree."

The work, publish today in the Proceeding of the National Academy of Sciences, not only raises the question of whether there is a connection between foreign DNA and the ability to survive extreme environments, but further stretches conventional views of how DNA is inherited.

First author Thomas Boothby, Goldstein and their collaborators revealed that tardigrades acquire about 6,000 foreign genes primarily from bacteria, but also from plants, fungi and Archaea, through a process called horizontal gene transfer - the swapping of genetic material between species as opposed to inheriting DNA exclusively from mom and dad. Previously another microscopic animal called the rotifer was the record-holder for having the most foreign DNA, but it has about half as much as the tardigrade. For comparison, most animals have less than one percent of their genome from foreign DNA.

"Animals that can survive extreme stresses may be particularly prone to acquiring foreign genes -- and bacterial genes might be better able to withstand stresses than animal ones," said Boothby, a postdoctoral fellow in Goldstein's lab. After all, bacteria have survived the Earth's most extreme environments for billions of years.

The team speculates that the DNA is getting into the genome randomly but what is being kept is what allows tardigrades to survive the harshest of environments, e.g. stick a tardigrade in a - 80 celsius freezer for a year or 10 and it starts running around in 20 minutes after thawing.

This is what the team thinks happens: when tardigrades are under conditions of extreme stress such as desiccation - or a state of extreme dryness -- Boothby and Goldstein believe that the tardigrade's DNA breaks into tiny pieces. When the cell rehydrates, the cell's membrane and nucleus, where the DNA resides, becomes temporarily leaky and DNA and other large molecules can pass through easily. Tardigrades not only can repair their own damaged DNA as the cell rehydrates but also stitch in the foreign DNA in the process, creating a mosaic of genes that come from different species.

"We think of the tree of life, with genetic material passing vertically from mom and dad," said Boothby. "But with horizontal gene transfer becoming more widely accepted and more well known, at least in certain organisms, it is beginning to change the way we think about evolution and inheritance of genetic material and the stability of genomes. So instead of thinking of the tree of life, we can think about the web of life and genetic material crossing from branch to branch. So it's exciting. We are beginning to adjust our understanding of how evolution works."
-end-
About the University of North Carolina at Chapel Hill

The University of North Carolina at Chapel Hill, the nation's first public university, is a global higher education leader known for innovative teaching, research and public service. A member of the prestigious Association of American Universities, Carolina regularly ranks as the best value for academic quality in U.S. public higher education. Now in its third century, the University offers 78 bachelor's, 112 master's, 68 doctorate and seven professional degree programs through 14 schools and the College of Arts and Sciences. Every day, faculty - including two Nobel laureates - staff and students shape their teaching, research and public service to meet North Carolina's most pressing needs in every region and all 100 counties. Carolina's more than 308,000 alumni live in all 50 states and 150 countries. More than 167,000 live in North Carolina.

University of North Carolina at Chapel Hill

Related DNA Articles from Brightsurf:

A new twist on DNA origami
A team* of scientists from ASU and Shanghai Jiao Tong University (SJTU) led by Hao Yan, ASU's Milton Glick Professor in the School of Molecular Sciences, and director of the ASU Biodesign Institute's Center for Molecular Design and Biomimetics, has just announced the creation of a new type of meta-DNA structures that will open up the fields of optoelectronics (including information storage and encryption) as well as synthetic biology.

Solving a DNA mystery
''A watched pot never boils,'' as the saying goes, but that was not the case for UC Santa Barbara researchers watching a ''pot'' of liquids formed from DNA.

Junk DNA might be really, really useful for biocomputing
When you don't understand how things work, it's not unusual to think of them as just plain old junk.

Designing DNA from scratch: Engineering the functions of micrometer-sized DNA droplets
Scientists at Tokyo Institute of Technology (Tokyo Tech) have constructed ''DNA droplets'' comprising designed DNA nanostructures.

Does DNA in the water tell us how many fish are there?
Researchers have developed a new non-invasive method to count individual fish by measuring the concentration of environmental DNA in the water, which could be applied for quantitative monitoring of aquatic ecosystems.

Zigzag DNA
How the cell organizes DNA into tightly packed chromosomes. Nature publication by Delft University of Technology and EMBL Heidelberg.

Scientists now know what DNA's chaperone looks like
Researchers have discovered the structure of the FACT protein -- a mysterious protein central to the functioning of DNA.

DNA is like everything else: it's not what you have, but how you use it
A new paradigm for reading out genetic information in DNA is described by Dr.

A new spin on DNA
For decades, researchers have chased ways to study biological machines.

From face to DNA: New method aims to improve match between DNA sample and face database
Predicting what someone's face looks like based on a DNA sample remains a hard nut to crack for science.

Read More: DNA News and DNA Current Events
Brightsurf.com is a participant in the Amazon Services LLC Associates Program, an affiliate advertising program designed to provide a means for sites to earn advertising fees by advertising and linking to Amazon.com.