A chimera is an organism made up of genetically heterogeneous cells. In animals, chimeras are called organisms whose cells are derived from two or more zygotes . Chimerism in animals should be distinguished from mosaicism - the presence in a single organism of genetically heterogeneous cells originating from one zygote [1] . Often chimerically constructed are not whole organisms, but only their individual organs or parts [2] .
In 1907, the term was first used by the German botanist G. Winkler for plant forms that were obtained as a result of merging of nightshade and tomato [3] .
In 1909, E. Baur , studying variegated pelargonium , found out the nature of this phenomenon [3] .
Natural chimeras were first described by M.S. Navashin . In particular, he discovered the chimeras Crepis dioscoridis L. [3] and Crepis tectorum L. [4] Natural haplochlamide periclinal chimeras were first described by L. P. Breslavets on the example of individual geographical hemp races [5] .
Content
Chimerism in plants
Chimeras can occur in nature as a result of spontaneous mutations of somatic cells , under experimental conditions (treatment with mutagens , polyploidogens , colchicine , other influences), as well as among regenerated plants and as a result of vaccinations . Chimeras are more common in plants propagated by the vegetative method , since only with this method the chimera persists for a sufficiently long time. During sexual reproduction , chimera arising from the instability of alleles is possible. In this case, the inheritance of characters is not subject to Mendelian laws and is considered an unstable mutation. In nature, chimeras are rare; they arise, as a rule, as a result of random hybridization and mechanical damage [5] .
Chimeras (especially periclinal, as more stable) with a range of economic advantages are important in crop production . They are often grown as ornamental plants [6] .
In botany, the following types of chimeras are distinguished (see table).
| Type of chimera | Features |
|---|---|
| mosaic (hyperchimeras) | genetically different tissues form a thin mosaic |
| sectorial | heterogeneous tissues are located in large areas |
| periclinal | tissues lie one above the other |
| mericlinal | tissues consist of a mixture of sectorial and periclinal sites |
Periclinal chimeras are:
- diplochlamide (e.g. pelargonium with white-fringed leaves)
- haplochlamide (e.g. chlorophytum with white-fringed leaves)
Periclinal chimeras are more common in nature, due to their greater stability. Often they are found among vegetatively propagated varieties of ornamental plants [5] . So Juniperus davurica 'Expansa Variegata' is a periclinal chimera in which the external tissues are genotypically albino and the internal ones are composed of chlorophyll-bearing cells [7] .
The interaction between the components of the chimeras and the transition of various substances from one component to another can lead to various developmental anomalies and sometimes to infertility of the chimera.
In the practice of gardeners, chimeras that have arisen accidentally as a result of vaccinations (the so-called variegation) are reproduced by vegetative propagation again from generation to generation (for example, chimeras between purple broom and golden rain - the so-called Adam broom, chimeras between orange and lemon ) . Researchers use various chimeras between the medlar and hawthorn .
Unsetting
The loss of chimera is characteristic of both plants obtained as a result of treatment with colchicine and chimeras that arose spontaneously. Along with periclinal chimeras that retain their characteristics during vegetative propagation for 100 years or more [3] , cases of the disappearance of chimera are described (in the trichimer Pelargonium zonaie , the orange 'Shamouti' , known since the 19th century , etc.). In some forms of grapes, desimetration can occur on separate shoots, while the lower part of the shoots consists of polyploid tissues [5] .
The frequency of desimetration depends on the method of plant propagation. Propagation by root cuttings more often leads to desymerization than vegetative propagation by other parts of the plant [5] .
Animal Chimerism
In animals, chimeras are called organisms that consist of genetically different cells that come from two or more different zygotes .
An example of animal chimerism is the frimartinism of cows and other animals. Frimartinism is a type of abnormal hermaphroditism , accompanied by sterility , in which the females develop both ovaries and testicles. Female calves from pairs of heterosexual twins are exposed to this phenomenon. Frimartinism is explained by the formation of vascular anastomoses between heterosexual fruits, as a result of which there is an exchange of sex hormones and progenitors of germ cells [8] [1] . A similar phenomenon was found in marmosets , but in them it does not lead to sterility [8] .
Chimeras can be formed from four gametes (the result of combining two fertilized eggs or embryos in the early stages of development into one embryo).
Chimerism in animals can be both the result of the individual development of the body ( ontogenesis ), and the result of transplantation of an organ, tissue (for example, bone marrow or blood transfusion). Chimeras can often produce offspring, and the type of offspring depends on which line of cells the gametes evolved from.
In the 1980s, an interspecific chimera of sheep and goats was artificially obtained.
In 2017, scientists from the Salk Institute created an embryo of a chimera - a pig with human cells [9] .
Human Chimerism
In humans, chimerism can occur at different stages of ontogenetic development: at the time of fertilization, embryonic development or in adulthood.
Fertilization Chimerism
Several cases of tetragamet chimerism in humans have been described. Such chimeras arise when two different zygotes merge shortly after fertilization and form a single embryo. Such chimeras are identified, for example, by the presence of two populations of red blood cells , hermaphroditism, and sometimes by the mosaic color of the skin and eyes [10] .
Fetal and maternal microchemeries
Microchimerism occurs when the cells of the mother and fetus penetrate the placental barrier of mammals and are normally characterized by a small fraction of “foreign” cells in the body.
There are two types of microchimerism: fetal microchimerism — the presence of fetal cells in the mother’s body and maternal microchimerism — the presence of mother cells in the fetal organism, and then the baby. It is assumed that microchemerization due to the difference in the immune properties of the acquired cells and the cells of the host organism is the cause of a number of autoimmune diseases : juvenile dermatomyositis and neonatal lupus with fetal microchimerism, preeclampsia , systemic lupus erythematosus and some forms of cancer with maternal microchemerization, as well as a number of other pathological conditions .
If the patient’s blood contains human cells of the opposite sex, chimerism is easy to detect by detecting cells with female and male karyotypes . In other cases, the blood cells of the patient are typed by HLA .
Twins Chimerism
As in some other mammals, in humans, the exchange of cells between twins is possible during intrauterine development. Cell migration occurs through a common placenta (placental anastomoses).
Homozygous twins
Theoretically, chimerism in homozygous twins is impossible, since they are genetically identical and come from one zygote. However, rare observations show that cell exchange between such twins still occurs. A case of monochorionic diamniotic pregnancy is described, in which trisomy of 21 chromosomes occurred in one of the twins at an early stage of development. At birth, one of the twins had phenotypic signs of Down's syndrome, the second had a normal phenotype. Analysis of microsatellite DNA showed that the twins were truly homozygous. Moreover, in the epithelial cells of the oral cavity of each twin, only its own cells (disomic or trisomic with 21 chromosomes) were detected, while the blood contained cells of both twins. This phenomenon is called chimerism of blood cells and is explained by the fact that twins with a monochorionic placenta in 70% of cases exchange blood at one stage or another of development [11] .
Heterozygous twins
As a rule, heterozygous twins in humans have their own placenta. However, several cases have been described when heterozygous twins were fed from the common placenta. In this situation, blood is exchanged between twins who are not genetically identical, which leads to the chimerism of blood cells and, possibly, other tissues. It is believed that the frequency of this phenomenon is underestimated and increases with the use of assisted reproductive technologies [8] [1] .
In Culture
Chimerism is detected in a patient in the 2nd series of the 3rd season of the series “ House MD ”.
Chimerism is repeatedly mentioned and is one of the key points in understanding the plot in the series "The Dark Child ".
Chimerism was also found in the killer in episode 23 of season 4 of the series CSI: Crime Scene .
See also
- Mosaicism
- Vegetative Hybridization
- Lydia Fairchild
Notes
- ↑ 1 2 3 Abuelo D. Clinical significance of chimerism // Am J Med Genet C Semin Med Genet. - 2009. - T. 151C , no. 2 . - S. 148-51 . - DOI : 10.1002 / ajmg.c.30213 . - PMID 19378333 .
- ↑ Chimeras (Inaccessible link) . Big Medical Encyclopedia. Date of treatment March 14, 2013. Archived on April 3, 2014.
- ↑ 1 2 3 4 Krenke N.P. Plant Chimeras . - M — L.: Academy of Sciences of the USSR, 1947 .-- 386 p.
- ↑ Nsvashin M. Unbalanced somatic chromosomal variation in Crepis // Univ. California Publs. Agriculture. Sci .. - 1930. - T. 6 , No. 3 . - S. 95-106 .
- ↑ 1 2 3 4 5 Kunakh V. A. Genomic variability of somatic plant cells // Biopolymers and Cell. - 1995. - T. 11 , No. 6 .
- ↑ Kren M. B., Lawrence W. J. C. Genetics of garden and vegetable plants. - M. - L .: Selkhozgiz, 1936 .-- 232 p.
- ↑ Ruth J., Klekowski EJ, Jr., Stein OL Impermanent initials of the shoot apex and diplontic selection in a juniper chimera // Am. J. Bot .. - 1985. - No. 72 . - S. 1127–1135 .
- ↑ 1 2 3 Chen K., Chmait RH, Vanderbilt D., Wu S., Randolph L. Chimerism in monochorionic dizygotic twins: case study and review // Am J Med Genet A. - 2013 .-- T. 161A , no. 7 . - S. 1817-24 . - DOI : 10.1002 / ajmg.a.35957 . - PMID 23703979 .
- ↑ Scientists created the chimera , theUK.one (January 27, 2017).
- ↑ Yu N., Kruskall MS, Yunis JJ, Knoll JH, Uhl L., Alosco S., Ohashi M., Clavijo O., Husain Z., Yunis EJ, Yunis JJ, Yunis EJ Disputed maternity leading to identification of tetragametic chimerism // N Engl J Med. - 2002. - T. 346 , no. 20 . - S. 1545-52 . - PMID 12015394 .
- ↑ O'Donnell CP, Pertile MD, Sheffield LJ, Sampson A. Monozygotic twins with discordant karyotypes: a case report // J Pediatr. - 2004 .-- T. 145 , no. 3 . - S. 406-8 . - PMID 15343200 .
Literature
- Uptake of informative molecules by living cells, ed. L. Ledoux, Arnst. - L., 1972; Hess D., Transformationen an höheren Organismen, Naturwissenschaften, 1972, Jg. 59.
- Baruch Rinkevich. Human natural Chimerism: an acquired character or a vestige of evolution? Human Immunology, vol. 62, No. 6 (June 2001), pp. 651—657
- The meaning of the word "Chimeras (in biology)" in the Great Soviet Encyclopedia
Links
- Lineberger R. Origin, development and reproduction of chimeras on the Cultivar website
- Problems of regulation of the creation of hybrids of animals and people // Wikinews