Tardigrades are remarkably resilient due to their DNA, a large part of which is surprisingly inherited from foreign sources. A new exciting research paper featuring in the Proceeding of the National Academy of Sciences journal explains why tardigrades or water bears are such remarkably unique organisms.
Authored by researchers with the University of North Carolina at Chapel Hill, the research paper gives a potential explanation as per the water bear’s ability to survive extreme conditions and environments. From freezing to living in outer space, to being dropped in boiling water, tardigrades are remarkably resilient due to their DNA.
To shed light on the possible source of their strength and resilience, the research team sequenced the genome of the water bear. What the team found was nothing short of surprising: 17.5 percent of the tardigrade’s DNA is foreign. Typically, organisms have 1 percent of foreign DNA. Bob Goldstein, co-author on the research paper, declared that previously it was unheard of any organism and animal genome to have such a large sequence of foreign DNA. The process of acquiring foreign genes is not new. Yet, the degree to which it was observed in the tardigrade took scientists by surprise.
While this finding is important by itself, it also raises questions as to the relation between foreign DNA and the remarkable resilience exhibited by the water bear as well as to the process through which inheriting foreign DNA is possible.
The genome sequencing revealed that the tardigrade sports 6,000 foreign genes. These are inherited from bacteria, from fungi, plants and Archaea. The process that allows the transfer of foreign genes is known as horizontal gene transfer. As to how it manifests in the case of the water bear, that remains an open question.
The research team suggests that foreign DNA is acquired as a result of the tardigrade’s ability to repair damaged DNA and cells almost immediately after they have suffered a shock in an harsh environment.
For instance, if the water bear is in a state of desiccation, its DNA will break into several tiny pieces. As it exits desiccation, the cell rehydrates. The nucleus and the membrane of the cell are leaky for a short period of time, which allows large molecules and foreign DNA to enter. While the cell is rehydrating, it is repairing damaged DNA while also stitching new, foreign DNA. Thus the 6,000 foreign genes mosaic.
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