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Genomes and genome sequencing

Tardigrade genomes vary in size, from about 75 to 800 mega base pairs of DNA. Hypsibius exemplaris (formerly Hypsibius dujardini) has a compact genome of 100 megabase pairs and a generation time of about two weeks; it can be cultured indefinitely and cryopreserved.

The genome of Ramazzottius varieornatus, one of the most stress-tolerant species of tardigrades, was sequenced by a team of researchers from the University of Tokyo in 2015. While previous research had claimed that around one-sixth of the genome had been acquired from other organisms, it is now known that less than 1.2% of its genes were the result of horizontal gene transfer. They also found evidence of a loss of gene pathways that are known to promote damage due to stress. This study also found a high expression of novel tardigrade-unique proteins, including Damage suppressor (Dsup), which was shown to protect against DNA damage from X-ray radiation. The same team applied the Dsup protein to human cultured cells and found that it suppressed X-ray damage to the human cells by around 40%. While the exact mechanism of DNA protection is largely unknown, the results from an August 2020 study suggest that strong electrostatic attractions along with high protein flexibility help form a molecular aggregate, which allows Dsup to shield DNA.

The Dsup proteins of tardigrades Ramazzottius varieornatus and Hypsibius exemplaris promote survival by binding to nucleosomes and protecting chromosomal DNA from hydroxyl radicals. The Dsup protein of R. varieornatus also confers resistance to ultraviolet-C by upregulating DNA repair genes that protect the genomic DNA from the damages introduced by UV irradiation.