• Tardigrades Model Animals Tolerant To Varios Extreme Environments
  • Niloofar Torkzadeh,1,* Mozhgan shirazi,2
    1. Department of Biochemistry, Islamic Azad University, Falavarjan,Iran
    2. Department of Biology, Scince and Reserch Branch, Islamic Azad University, Tehran, iran


  • Introduction: Extremphiles are organisms that have adapted or least tolerant to extremely harsh environments. Most Extremophiles are single organisms with simple structure, such as archaea and bacteria. However, some animals also exhibit extraordinary tolerance against extreme environment. One of the most known example of such extremotolerant animals is the tardigrade.
  • Methods: Extremphiles are organisms that have adapted or least tolerant to extremely harsh environments. Most Extremophiles are single organisms with simple structure, such as archaea and bacteria. However, some animals also exhibit extraordinary tolerance against extreme environment. One of the most known example of such extremotolerant animals is the tardigrade.
  • Results: tardigrades, also known as water bear, are tiny aquatic animals having four pairs of legs. More than 1.000 speceies have been reported from various habitats such as marine, fresh water or limno_ terrestrial environments. All tardigrades require surrounding water to grow and reproduce, but some limn_terrestrial species are able to tolerate almost complete dehydration. When the surrounding water evaporates, tolerant tardigrades lose almost all body water and enter a metabolically in active dehydrated called anhydroiosis. Genomic DNA stores all genetic information and is in dispensable for maintenance of normal cellular activity and propagation. Radiation causes severe DNA lesion, including double_strand breaks, and leads to genome instability and even lethality. Regardless of the toxicity of radiation, some organisms exhibit extraordinary tolerance against radiation. These organisms are supposed to possess special mechanisms to mitigate radiation_induced DNA damages. Here we deter mine a nigh quality genome sequence of Ramazzottius varieornatus on of the most strees tolerant tardigrade spece. R.varieornatus is one of the most radiotolerant speciesin tardigrades. Considering DNA as a major target of radiation damage, the tardigrade is assumed to possess some protein associated with DNA to protect and/ or effectively repair DNA. Recently, as a representative of such proteins, damage suppressor (DSUP) Was identified from a chromation fraction of the tardigrade. In this review, we summarized the current know ledgs of extremely radiotilerant animals, mainy focusing on tardigrades as an emerging animal model of extremophiles. Antioxidant defenses and the efficient DNA rapair by protected enzymes have been accepted as a common basis for elevated radiotolerance shared from prokaryotes to animals. The recent genome analyes revaled that tardigrades also possess redundant copies of antioxidant enzymes and DNA repair enzymes while lacking ROS- producing enzymes, so a similar principle could be applicable to tardigrades as well. Although the precise mechanism of DNA protection by DSUP protein remain to be elucidated, the association with DNA is important for protection activity of DSUP protein, suggesting a possible physical shielding of DNA from ROS and irradiation and/or a local detoxification of ROS as potential mechanisms.
  • Conclusion: minor change in the gene expression profiles during dehydration and rehydration suggest constitutive expression of tolerance related gene. The findings indicate the relevance of tardigrade unique proteins to tolerability and tardigrades could be a bountiful source of new protection genes and mechanism.
  • Keywords: Tardigrade, Genomic, Radiotolerance, Damage Suppressor(DSUP), Space Biology