An international group of biologists read rotifers Adineta vaga genome and found that these organisms have renounced sexual reproduction millions of years ago , because of acquired characteristics of the genome are no longer able to return to it . The research is published in the journal Nature.
A key differentiator of the genome Adineta vaga, according to scientists , is " shuffling " in it alleles . Those genes that in organisms with sexual reproduction are located on paired chromosomes in rotifers confused - and baseline maternal and paternal copies from baseline Adineta vaga are often found on the same chromosome. This makes it impossible for normal sexual reproduction , as in the formation of gametes ( meiosis ) occurs pairing of chromosomes c subsequent exchange genes ( crossing-over ), and rotifers have many genes simply do not mate with whom .
Despite the fact that male rotifers never failed to detect , scientists still could not rule out that they have a certain sexual process in the very rare cases ( even among "normal" rate of microorganisms is asexual reproduction , and to the sexual process , they resort very rare).
Furthermore , the reading Adineta vaga genome revealed that about 8 percent of the total DNA sequence of invertebrate represent " stolen " from the bacteria and other microorganisms. That rotifers easily include foreign DNA into their genome , and it is maintained by a variety of species , has been known since 2008. However, to read the full genome scale of this process was not clear.
Abandonment of sexual reproduction occurs quite often in different groups of animals, but such a process always leads to a relatively rapid extinction . Microscopic multicellular rotifers, which can usually be found in pools and other freshwater bodies , are an exception to this rule. This group exists without sexual reproduction seems to have a few million years and managed to split into more than four hundred species. The success of parthenogenesis in rotifers have been linked to the fact that these animals are very easy to borrow someone else's genetic information , and thus maintain their diversity.
Japanese research team was able to get a miniature human liver from stem cells. Pluripotent stem cells turned into a disk diameter of 4 millimeters , which confirmed its efficiency , being transplanted in experimental mice with the failed own liver . Details of the work presented in the journal Nature, and briefly spoke about her Nature News.
Researchers have used the induced pluripotent stem cells , i.e. stem cells , obtained by reprogramming the mature adult cells . Then they succeeded in transforming both hepatocytes and cells of blood vessels and connective tissue, scientists have three-dimensional structure , a histological analysis showed that all required elements for the liver .
Transplant grown in test tubes miniature drives about four millimeters in diameter experimental mice demonstrated performance artificial liver . Two days after surgery the blood vessels of the animal connected with the vessels of the liver, and the cells continued to divide : the organ began to grow. The liver is known for its high capacity for regeneration , so patients who need a new liver , often transplanted small part of the body , taken from a living donor .
Talk about the imminent introduction into clinical practice of liver transplants of stem cells is not necessary. The researchers intend to observe the behavior of the first artificial liver in mice , to ensure its security and stability. Some previous research works have shown that induced stem cells regenerate in most tumor cells , so we first check the ability of the new liver to limit their growth and maintain the required functions .
Despite the fact that liver transplant patients are well established and after they can return to an active life , they can not be considered routine and affordable operation : immunologic restrictions hamper the selection of the donor. To address the shortage of scientists currently working in several ways : some groups are trying to collect the liver cell cultures from ready ( a liver already printed on the 3D- printer ) , others are trying to repeat the process of forming the body of stem cells from scratch.