Tiny wa­ter bears are huge DNA thieves

Kuwait Times - - HEALTH -

WASH­ING­TON: The eight-legged wa­ter bear-a hardy, nearly mi­cro­scopic an­i­mal re­sem­bling its mam­mal name­sake-gets a huge chunk of its DNA from for­eign or­gan­isms such as bac­te­ria and plants, sci­en­tists have re­vealed. Th­ese genes, the re­searchers sug­gest, help the tiny an­i­mals, also known as moss piglets or tardi­grades, sur­vive in the harsh­est of en­vi­ron­ments. Wa­ter bears, which live all over the world, are usu­ally 0.020 inches (0.5 mil­lime­ters) long and move very slowly and clum­sily on their mul­ti­tude of legs.

Th­ese highly adapt­able crea­tures can sur­vive ex­treme tem­per­a­tures. Even af­ter be­ing stuck in a freezer at -112 de­grees Fahren­heit (-80 Cel­sius) for 10 years, they can start mov­ing around again about 20 min­utes af­ter thaw­ing. By se­quenc­ing th­ese crea­tures’ genome, re­searchers from the Univer­sity of North Carolina (UNC) at Chapel Hill were sur­prised to find that 17.5 per­cent-nearly a sixth-of the genome came from for­eign or­gan­isms. For most an­i­mals, less than one per­cent of their genome comes from for­eign DNA. The mi­cro­scopic ro­tifer pre­vi­ously held the record, with eight per­cent of its genome com­ing from for­eign DNA. “We had no idea that an an­i­mal genome could be com­posed of so much for­eign DNA,” said co-au­thor Bob Goldstein of UNC’s Col­lege of Arts and Sci­ences. “We knew many an­i­mals ac­quire for­eign genes, but we had no idea that it hap­pens to this de­gree.”

New insight on evo­lu­tion The study, pub­lished in Mon­day’s edi­tion of the Pro­ceed­ings of the Na­tional Acad­emy of Sci­ences, also made un­usual find­ings about how DNA is in­her­ited. Goldstein, first au­thor Thomas Boothby and col­leagues found that wa­ter bears ob­tain about 6,000 for­eign genes mostly from bac­te­ria, as well as plants, fungi and Ar­chaea sin­gle-cell or­gan­isms. “An­i­mals that can sur­vive ex­treme stresses may be par­tic­u­larly prone to ac­quir­ing for­eign genes-and bac­te­rial genes might be bet­ter able to with­stand stresses than an­i­mal ones,” said Boothby, a post­doc­toral fel­low in Goldstein’s lab. In­deed, bac­te­ria have sur­vived the most ex­treme en­vi­ron­ments on Earth for bil­lions of years. Wa­ter bears ac­quire for­eign genes through hor­i­zon­tal gene trans­fer, a process by which species swap ge­netic ma­te­rial in­stead of in­her­it­ing DNA from par­ents. “With hor­i­zon­tal gene trans­fer be­com­ing more widely ac­cepted and more well-known, at least in cer­tain or­gan­isms, it is be­gin­ning to change the way we think about evo­lu­tion and in­her­i­tance of ge­netic ma­te­rial and the sta­bil­ity of genomes,” said Boothby. Re­searchers said the DNA likely gets in­side the genome ran­domly but what re­mains al­lows wa­ter bears to sur­vive in the most hos­tile en­vi­ron­ments.

Un­der in­tense stress, such as ex­treme dry­ness, the wa­ter bear’s DNA breaks up into small pieces, ac­cord­ing to the re­search team. Once the cell re­hy­drates, its mem­brane and nu­cleus hous­ing the DNA tem­po­rar­ily be­comes leaky and al­lows other large mol­e­cules to pass through eas­ily. They thus re­pair their own dam­aged DNA while also ab­sorb­ing for­eign DNA as the cell re­hy­drates, forming a patch­works of genes from dif­fer­ent species.

“So in­stead of think­ing of the tree of life, we can think about the web of life and ge­netic ma­te­rial cross­ing from branch to branch,” Boothby ex­plained. “So it’s ex­cit­ing. We are be­gin­ning to ad­just our un­der­stand­ing of how evo­lu­tion works.” — AFP

This im­age shows a light mi­cro­graph of a tardi­grade. — AFP

Newspapers in English

Newspapers from Kuwait

© PressReader. All rights reserved.