No sexual reproduction but still gene exchange

From where do we have our own genome? If it is an animal, a gene comes from a parent's conception, and that's it. There is no subsequent DNA combination, unless we have a parasite that lives on our body or a symbiotic entity somehow transforming a part of their gene to us (this is a rare case noted). Or else we must be bdelloid rotifer.

This strange freshwater animal, on a microscope, continues to transform again. This time a large number of strange DNA was found in their genome. In the article published this week in Science, evidence of the equal movement of large amounts of genes - from bacteria, fungi, even plants - to bdelloid rotifer's genome was Irina Arkhipova, Matthew Meselson, Scientist from Josephine Bay Paul Center of MBL and Harvard University, and graduate student Eugene Gladyshev at Harvard University.

Genetic migration is a common phenomenon in bacteria, but it has never been known in the animal kingdom of such large scale - until this study was done.

Arkhipova said: 'It is amazing that bdelloid has the ability to choose external genes, from a variety of sources, to operate in the new body. Bdelloid can use the whole gene in the environment, which is of significant importance in adaptation (by evolution) to the expansion into new ecological regions, even contributing to the formation process. bdellooid species'.

The experimental culture of bdelloid rotifer Adineta vaga.Rotifer can combine other species' DNA into their genome during the drying or dehydration stage of their life cycle.(Photo: Eugene Gladyshev)

This finding helps explain why bdelloids, a asexual species, can diversify into 360 species in 40 million years of evolution. People call this a 'evolutionary scandal'. Bdelloid denies the notion that sexual reproduction - combining parents' DNA in their offspring - creates a variety and a high adaptability for a species, and thus increases evolutionary success. Arkhipova's research suggests that if bdelloids can combine foreign DNA from the environment, they can also choose DNA from other bdelloids. From an evolutionary point of view, this phenomenon is similar to sexual reproduction.

How bdellooid can pool all kinds of genes in the environment to combine with its genome. In animals, genetic parts - eggs and sperm - are protected from environmental damage, such as the invasion of foreign DNA from the rest of the body's cells. Genetic power but serves the purpose of 'isolating' cell lines that carry out genetic tasks. Arkhipova said that the idea of ​​why the genetic part of bdelloid was exposed to the exchange environment 'is speculative'. 'But we talked about this issue many times.'

A major focal point is the viability of bdelloids over a completely dry period while most organisms must die. When water disappears from the habitat, bdelloid enters the dehydration stage and stops working. They can survive for months or even years. But as soon as the water appears, they immediately react, move, eat and start breeding.

Arkhipova said: In the dry period, 'the possibility of membrane damage and DNA in the rotifer is huge. Not only are rotifers dried, but so are all their food. If the DNA of both the rotifer and its food is broken during dryness, it is an opportunity for external DNA cells to penetrate the genetic organ of the rotifer. In the process of dehydration, fragments of DNA are somehow recovered, merging with foreign DNA from outside . '

This hypothesis is rooted in recent research by Gladyshev and Meselson (2008). This study indicates that bdelloid is particularly good at recovering after their DNA is broken by ionizing radiation. The rotifer's DNA repair ability can evolve due to the dry environment. Arkhipova said: 'The effects of radiation and drought are quite similar, both harming chromosomes as well as DNA films.'

Most foreign genes Arkhipova's team found in the bdelloid genome are concentrated near the top of the chromosome, called telomeres. Arkhipova said: If bdelloids choose foreign genes during drought, it may sometimes be to protect telomeres, as we have demonstrated for mobile factors in previous research (Gladyshev and Arkhipova, 2007 ). Or vice versa, the selection process does not work effectively to prevent toxic DNA from entering the gene pool of the chromosome. '