The tetraploid complementation assay is a technique in biology in which cells of two mammalian

embryo An embryo is an initial stage of development of a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sperm ...

s are combined to form a new embryo. It is used to construct

genetically modified organism A genetically modified organism (GMO) is any organism whose genetic material has been altered using genetic engineering techniques. The exact definition of a genetically modified organism and what constitutes genetic engineering varies, with ...

s, to study the consequences of certain mutations on embryonal development, and in the study of pluripotent stem cells.

Procedure

Normal mammalian somatic cells are

diploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respecti ...

: each

chromosome A chromosome is a long DNA molecule with part or all of the genetic material of an organism. In most chromosomes the very long thin DNA fibers are coated with packaging proteins; in eukaryotic cells the most important of these proteins ar ...

(and thus every

gene In biology, the word gene (from , ; "... Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

) is present in duplicate (excluding genes from X chromosome absent in Y chromosome). The assay starts with producing a ''tetraploid'' cell in which every chromosome exists fourfold. This is done by taking an embryo at the two-cell stage and fusing the two cells by applying an electrical current. The resulting tetraploid cell will continue to divide, and all daughter cells will also be tetraploid. Such a tetraploid embryo can develop normally to the

blastocyst The blastocyst is a structure formed in the early embryonic development of mammals. It possesses an inner cell mass (ICM) also known as the ''embryoblast'' which subsequently forms the embryo, and an outer layer of trophoblast cells called th ...

stage and will

implant Implant can refer to: Medicine *Implant (medicine), or specifically: ** Brain implant ** Breast implant **Buttock implant **Cochlear implant **Contraceptive implant **Dental implant ** Fetal tissue implant **Implantable cardioverter-defibrillator ...

in the wall of the

uterus The uterus (from Latin ''uterus'', plural ''uteri'') or womb () is the organ in the reproductive system of most female mammals, including humans that accommodates the embryonic and fetal development of one or more embryos until birth. The ...

. The tetraploid cells can form the extra-embryonic tissue (

placenta The placenta is a temporary embryonic and later fetal organ (anatomy), organ that begins embryonic development, developing from the blastocyst shortly after implantation (embryology), implantation. It plays critical roles in facilitating nutrien ...

, etc.); however, a proper

fetus A fetus or foetus (; plural fetuses, feti, foetuses, or foeti) is the unborn offspring that develops from an animal embryo. Following embryonic development the fetal stage of development takes place. In human prenatal development, fetal develo ...

will rarely develop. In the tetraploid complementation assay, one now combines such a tetraploid embryo (either at the

morula A morula (Latin, ''morus'': mulberry) is an early-stage embryo consisting of a solid ball of cells called blastomeres, contained in mammals, and other animals within the zona pellucida shell. The blastomeres are the daughter cells of the zygo ...

stage) with normal diploid embryonic stem cells (ES) from a different organism. The embryo will then develop normally; the fetus is exclusively derived from the ES cell, while the extra-embryonic tissues are exclusively derived from the tetraploid cells.

Applications

* Foreign genes or mutations can be introduced into ES cells rather easily, and these ES cells can then be grown into whole animals using the tetraploid complementation assay. * By introducing targeted mutations into the tetraploid cells and/or into the ES cells, one can study which genes are important for fetal development and which ones are important for development of the extra-embryonic tissues. * The tetraploid complementation assay is also used to test whether

induced pluripotent stem cell Induced pluripotent stem cells (also known as iPS cells or iPSCs) are a type of pluripotent stem cell that can be generated directly from a somatic cell. The iPSC technology was pioneered by Shinya Yamanaka's lab in Kyoto, Japan, who showed ...

s (stem cells artificially produced from differentiated cells, e.g. from skin cells) are as competent as normal embryonal stem cells. If a viable animal can be produced from an induced pluripotent stem cell using the tetraploid complementation assay, then the induced stem cells are deemed equivalent to embryonal stem cells. This was first shown in 2009.Lan Kang, Jianle Wang, Yu Zhang, Zhaohui Kou, Shaorong Gao. 2009. iPS cells can support full-term development of tetraploid blastocyst-complemented embryos. Cell Stem Cell.

References

{{reflist Stem cells Genetic engineering