Chimera from nature. Man with two DNA

January 27, 2012 17:09

In the laboratories of Mother Nature are very strange experiments: one twin absorbs the other right in the womb, the mother is not the mother of his children, and brothers and sisters are merged into a single organism to survive. Genetics catching nature for a hundred years, but the beat and still could not. So, we chimerism.

U.S. resident Lydia Fairchild was expecting a nasty surprise when, after a divorce, she applied for a social benefit. Her husband had to acknowledge paternity DNA analysis — and the latter showed that just Lydia is the mother of two children together (as well as the third, which she at the time was pregnant). At first it was assumed that the reason — the transplantation of tissue or blood transfusions, but no women, no children are not.
State sued for fraud. The situation was saved Mrs. Fairchild's lawyer — he gave the court an article from the "New England Journal of Medicine":
52-year old Boston teacher Karen Keegan needed a kidney transplant. Her three sons have agreed to be donors, but genetic analysis it was found that two of them are relatives of his mother! Studies have established a number of interesting facts: in particular, it was found out that Karen was a twin sister, who at an early stage of embryonic development merged with the surviving fetus. Boston teacher was a chimera — a creature, whose body are present, without disturbing each other, fabrics with different sets of genes.

In the precedent with Mrs. Fairchild everything was more difficult — children Lydia DNA proved only relationship with their grandmother, mother, Mrs. Fairchild. Only managed to find out through the analysis of hair, and the hair on the head and pubic women contain different genetic material. Mrs. Fairchild went dry from the water, and its history in 2006, dedicated to the transfer of "My twin is in me."
Officially recorded about forty cases of chimerism, in fact, there are many more. With high probability the chimera was a famous maniac Chikatilo, who did not match the data on blood group and semen. Sometimes chimerism randomly pops up when trying in vitro fertilization or artificial insemination: Scientists in Germany have described the patient, which in the body cells contain 99% female XX chromosome set and 1% — male, XY. As it turned out, her twin brother died at birth, but lived cells in the body sisters.
And this is only the cases presenting to the wider medical community.
Legs, wings and tail
The term "chimera" is taken from Greek mythology — a "composite" monster with the body of a goat, the head of a lion, a snake tail, and so it is generated by the ugly monsters — women-snake echidna and giant Typhon, were killed, according to one version, the hero Bellerophon. In biology, a chimera, as already mentioned, — a creature with diverse genetic material, co-existing in the same body. The first term was introduced in 1907 by German botanist Hans Winkler, called chimeras plants obtained by grafting a cutting nightshade on tomato. Explained the nature of the phenomenon other nerd — Erwin Baur. A first "compound" the animal was constructed in 1984 — an artificial "mosaic" sheep and goats, baby four parents, some of the cells which contain the sheep genome, and some — goat.
Chimerism in plants — the result of natural mutation or vaccination, when a branch of one kind of hooked to the trunk of the other. Experiments with the famous Luther Burbank Russet Burbank, potato varieties, which now account for 50% of the crop of potatoes in the United States, seedless plums and quince-scented pineapple were largely the creation of Frankenstein in the plant world.
Engaged in the same famous Michurin who studied in full detail the effect of a stock (the young plant to which foreign podsazhivayut cutting) on the yield, viability and other properties of the graft. The reaction of "graft versus host" which caused so dangerous organ transplants in humans and animals, plants, in general, is alien. The only problem — the green chimera usually do not convey the qualities inherited, they must be propagated vegetatively.
Chimerism in mammals may be the result of several processes, both natural and artificial. The first — the so-called tetragametichesky chimerism when merged together two eggs, each fertilized by his sperm or two embryos in the early stages of development, so that the different organs and cells of the body contain different chromosome set. Stories with "absorbed twin" — a typical example of such chimerism.
Second — microchimerism. Baby cells can enter the blood stream and the mother to take root in its tissues (fetal microchimerism). For example, the immune cells of the fetus can be (at least for a few years) to cure his mother from rheumatoid arthritis, to help restore the heart muscle after which developed during pregnancy, heart failure, or increase the resilience of maternal cancer. Conversely, the cells pass through the mother's placenta to the fetus (maternal microchimerism). Not without its help, a system of innate immunity: the immune system of the fetus, "coach" for resistance to diseases, which developed an immunity to the mother. The flip side of the coin — that the child in the womb can be a victim of her own illness. In particular, such an autoimmune disease like lupus infants is common in children whose mothers suffer from systemic lupus erythematosus.
The third option of natural chimerism — "twin", when the blood vessels due to adhesions heterozygous twins pass each other the cell (not the same as homozygous, and with just as the brothers and sisters of differing sets of genes). So began a chimera aforementioned patient from Germany.

The next version of chimerism — post-transplant, when, after a blood transfusion or organ transplantation in humans own cells coexist with donor cells. Very rare, but it happens that the donor cells completely "integrated" into the body of the recipient — so, a few years ago, an Australian girl after liver transplantation forever changed blood type.
The last option — a bone marrow transplant, in which doctors are working hard to make the chimera of the patient and make the transplanted cells in place of the master's work.
Patient's own bone marrow are killed by irradiation and special preparations are introduced in its place the donor hematopoietic cells and waiting. If the tests reveal the donor chimerism — everyone is happy, the process goes, and if you can deal with graft rejection, there are chances of recovery. But the return of the "native" cells means early relapse.
Laboratory chimeras
History of chimeric embryos began with Dr. Ray Owen steers and chickens Dr. Peter Brian Medawar, which made it possible to develop a mechanism chimerization.
Calves and chickens Owen first to notice that the twin calves in the body cells coexist well with diverse genetic material, and the reason for that — fusion of blood vessels. And Dr. Medawar first spliced sawed in shell "window" of the eggs, then experimented on the introduction of cell culture ducks in chicken embryos, then began to connect the blood of chick embryos, and finally formulated the term "immunological tolerance" — a willingness to accept other people's body cells. He first hoisted mice embryos one clean line embryo cells another, and then transplanted skin grafts surviving chimeras to demonstrate: the transplanted biomaterials retain the properties of the native organism and is not rejected. Scientists Chicago and Liverpool have constructed chimeras in labs forest and home of mice by introducing additional genetic material into embryos at the blastocyst stage.
Pups were quite viable: more active than domestic mouse, but less active than forest. Russia has successfully grown chicken chimeras — white leghorn with red tails rodaylendov.
Toy Men
Another option to create chimeras — the introduction of human DNA into animal egg. Genetic material cybrids — cell hybrids — is almost entirely human, the animal they receive only the mitochondrial DNA. It is true that attempts to bring the hybrid embryos to birth chimeras to-date science is doomed to failure and, besides, human cloning and the creation of a human-animal chimeras prohibited by law in all countries. And there is no point in challenging experiments. Several dozen tsibridnyh embryos created purely for research purposes, were destroyed in a few days after the start dividing egg.
Doctors and homunculi
It took scientists about twenty years (since the first successful operation of Dr. Thomas), to learn how to pick the donor and recipient are compatible to human leukocyte antigens — proteins, which triggers a cascade of mismatch of molecular reactions that lead to the rejection of the transplant, and deal with rejection with drugs suppress the immune system. By 1990, there were about 4,000 bone marrow transplants — less than it is today held in the year. Now the five-year survival rate (in fact — recovery) in acute leukemia is 65%. Accordingly, it is possible to observe the unexpected effects of chimerism.
The point is that after the transplant can change blood type, Rh factor and the structure of the hair, and has long been ready to doctors and relatives of patients — but not all.
The fact that bone marrow transplants can cure even AIDS — an accidental discovery, the luck of German physicians. It is known that about 1% of Europeans resistant to HIV. A 42-year-old American, suffering and lymphoma, and AIDS was a bone marrow transplant to get rid of one of their illnesses. And to everyone's surprise (including doctors) was cured of both — its donors were carriers of the mutation that provides resistance to the virus, and gave it to the recipient along with the bone marrow.
Know-how of the XXI century — development on fetal stem cell therapy. Blood stem cells enter the fetus, immunodeficiency, thalassemia, granulocytosis — and theoretically the child to be born healthy. Almost managed to achieve the effect of a fetus with immunodeficiency, in all other cases, even with minimal chimerism disease did not diminish. Active in animal experiments were conducted on the treatment: first, to "turn off" the immunity of the fetus, and then spend transplant. But to human experimentation so far away.
Chimerism for good
Medicine has put the possibility of chimerism his service even before studied this phenomenon in its entirety. In 1940 he made the first attempt to transplant patients with aplastic anemia, bone marrow to his brother. In 1958, the bone marrow was treated in Paris six Yugoslav physicists injured in the accident at the nuclear power plant, five of whom survived. In 1957, the U.S. managed to Dr. Edward Thomas (after total body irradiation) to achieve engraftment in two children with leukemia. Children soon died, and after 10 years of 417 held by Thomas transplants successful were only three. In 1968 he was made completely successful transplantation: a child with severe immunodeficiency entered the marrow of his brother. The patient recovered and became a chimera — instead of their own blood into the cells of the body to produce "brotherly." And Edward Thomas in 1990 received the Nobel Prize in Medicine.

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