DNA studies have shed light on the origins and extraordinary survival ability of microscopic creatures known as tardigrades.
An international team of researchers has examined the DNA code for two species of tardigrade – also known as water bears or moss piglets, owing to their unusual appearance. The animals are well-known for being able to withstand extreme conditions, such as dehydration, freezing, radiation and outer space. Scientists hope better understanding of the genes that make tardigrades so tough might lead to new biotechnology and medical applications.
Tree of life
Researchers from the Universities of Edinburgh and Keio, Japan, examined tardigrade genes and were surprised to find that they had more in common with roundworms than with insects. Further study of so-called HOX genes, which inform the nose-to-tail pattern in embryos, found that tardigrades were missing five of these genes, in common with most roundworm species. As tardigrades have eight stubby legs, and insects and similar creatures have legs, this suggests that roundworms may have evolved to lose theirs.
Scientists were also able to identify the genes that help tardigrades to resist the effects of extreme dehydration. By identifying which genes were active during the drying process, they were able to pinpoint sets of proteins that appear to replace the water lost by cells. These help to preserve the structure of the animals' cells until water is available again.Other proteins seem to protect the tardigrades' DNA from damage, and may explain why they can survive radiation.
The new research has laid to rest suggestions that tardigrade DNA was a mix of animal and bacterial genes. This is now attributed to contamination in earlier studies. The study is published in PLOS Biology. The Edinburgh team were partly funded by the BBSRC.
I have been fascinated by these tiny, endearing animals for two decades. It is wonderful to finally have their true genomes, and to begin to understand them. This is just the start – with the DNA blueprint we can now find out how tardigrades resist extremes. It has been great to work with Japanese colleagues on this – science is truly global, and together we achieved exciting things.
Professor Mark Blaxter, School of Biological Sciences
Sinclair Stammers www.micromacro.co.uk