Permanent gene editing of tardigrades helps explain their amazing resilience

Certain species of tardigrades are highly and unusually resistant to a variety of extreme conditions that are fatal to most other forms of life. The genetic basis of these exceptional abilities remains elusive.

For the first time, scientists at the University of Tokyo have successfully edited genes using the CRISPR technique in a highly resistant tardigrade species that previously could not be studied using genome editing tools. The work was published in PLoS Genetics.

Successful delivery of CRISPR to an asexual tardigrade species directly produces gene-edited offspring. Designing and editing specific tardigrade genes allows researchers to investigate which are responsible for tardigrade resistance and how such resistance might work.

If you’ve heard of tardigrades, then you’ve undoubtedly heard of their unusual abilities to survive things like extreme heat, cold, drought, and even the vacuum of space that various members of the species possess. So they naturally attract researchers who want to explore these novelties, not just out of curiosity, but to see what applications might one day be possible if we could learn their secrets.

“To understand the superpowers of tardigrades, we first need to understand how their genes work,” said Associate Professor Takekazu Kunieda from the Department of Biological Sciences.

“My team and I have developed a method for editing genes – adding, deleting or rewriting them – as you would on computer data, in a very tolerant species of tardigrade, Ramazzottius varieornatus. This now allows researchers to study the genetic characteristics of tardigrades as they may be more established laboratory animals such as fruit flies or nematodes.”

The team used a recently developed technique called direct parental CRISPR (DIPA-CRISPR), based on the now known CRISPR gene editing technique, which can serve as a genetic scalpel to cut and modify specific genes more efficiently than ever before. DIPA-CRISPR has the advantage of being able to affect the genome of a target organism’s offspring and has previously been shown to work on insects, but this is the first time it has been used on non-insect organisms, which include tardigrades.

Ramazzottius varieornatus is an all-female species that reproduces asexually, and almost all offspring have been shown to have two identical copies of the same edited code, unlike other animals, making it an ideal candidate for DIPA-CRISPR.

“We simply needed to inject CRISPR tools programmed to target specific genes for deletion into the parent’s body to obtain edited offspring, known as ‘knock-out’ edits,” said Koyuki Kondo, a researcher on the project at the time of the study (currently an assistant professor in the Department of Natural Sciences at Chiba Institute of Technology).

“We could also obtain genetically modified offspring by injecting additional DNA fragments that we want to include; this is called ‘knock-in’ editing. The availability of knock-in editing allows researchers to precisely edit tardigrade genomes, allowing them to, for example, control how individual genes are expressed or show the functions of genes.”

The main feature of this species’ resilience is their ability to survive extreme dehydration for long periods of time. This was previously shown to be partly due to a special type of gel protein in their cells. And this property is interesting because it has also been applied to human cells.

Kunieda and other tardigrade researchers think it’s worth investigating whether something like an entire human organ could one day be successfully dehydrated and rehydrated without degradation. If possible, it could revolutionize the way organs are donated, transported and used in life-saving surgery.

“I understand that some people are concerned about gene editing, but we conducted our gene editing experiments under well-controlled conditions and secured the engineered organisms in a confined space,” Kunieda said.

“CRISPR can be an incredible tool for understanding life and helping with useful applications that can positively impact the world. Tardigrades not only offer us a glimpse of what medical advances might be possible, but their array of remarkable properties means they have had an incredible evolutionary story .” We hope to reveal this by comparing their genomes with closely related creatures using our new DIPA-CRIPSR-based technique.”