American biologists have managed to create a chimeric human embryos and mouse in which the proportion of human cells was up to four percent. In previous experiments, human cells were built in such embryos is bad, and they are not always able to detect. Progress has been made possible thanks to special treatment of embryonic stem cells: researchers “stalled” development by synchronizing their state with an embryonic mouse cells. Human cells are penetrated in a variety of organs, from the liver to the retina. Work published in the journal Science Advances.
Chimeric embryos from different mammalian species is not only a tool for the study of embryonic development, but promising biotechnology. Scientists have repeatedly offered to use animals as incubators for growing human organs. Such chimeric embryos already created, not only for laboratory organisms, e.g., mice and rats — but also with human cells.
So, a few years ago received the Chimera man-pig, and in the summer of 2019 Spanish scientists have stated that has created in China a Chimera of APE. However, all of these embryos are destroyed in the early stages of development, to avoid the ethical controversy. And only in the summer of 2019 Japanese scientists received permission to not only enter human cells in the mouse embryo, but also implanting the Chimera into the uterus of pregnant mice.
The problem is this: on the stage of development where possible the creation of chimeras, human cells and mouse are in different States. The embryo of a mouse at this point consists of naive embryonic stem cells (ESCs) are able to give rise to all embryonic and some nazaralieva tissues. Human cells at this stage are called premenovanie ESK — nazaralieva of them fabric will not work because they have already started differentiation.
Now there are several ways to transfer human ESC from primitivnogo state in naive, for example, chemical inhibitors or expression of specific genes (we also spoke about a mechanical way). But in all these cases, the efficiency of integration into the germ postimplantation low: in the chimeras of the man-pig had managed to notice only a few human cells in the chimeras human-mouse , they are almost not possible to see.
Jian Feng (Jiang Feng) from the new York state University in Buffalo and his colleagues have proposed another method of solving the problem. The fact that naive murine ESCs can be associated with diapause — a condition in which the embryo development is inhibited while the mother bears or brings up the previous generation of cubs. It is also known that diapause from mouse embryos can be called if you block the protein mTOR complex which boosts cellular metabolism. Therefore, Feng and colleagues suggested that can be treated human ESCs blockers mTOR and thereby be synchronized with the cells in the mouse embryo.
To begin with, the researchers checked that their chosen method works. They have developed a Protocol involving common blocker of mTOR — rapamycin and alternative blocker — Torin1. Received a colony of naive ESCs was expressed all the necessary markers to form tumors (teratomas) when injected into mice, i.e. satisfy the criteria of embryonic cells. However, their functional properties have changed: for example, they are better to share. While the original culture primitivnykh ESK has increased 10 times in 6 days, the culture of naive ESCs — almost 1000 times. The changes also affected the expression of genes and the level of DNA methylation.
Then the authors introduced a naive human ESC expressing green fluorescent protein in mouse morula — embryos the early days of development, which are simply a group of identical cells. Of chimeric moral developed blastocyst cell balls with a loose mass inside — and human cells glowed as the outer layer and in the internal. Further, these blastocysts hoisted the mice and the embryos were taken for analysis until the 17th day of development (counting from the moment of fertilization). Researchers interested in what kind of fabric can be incorporated into human cells. In the end, they were detected in the liver (derived inner germ layer, endoderm) and in the retina (a derivative of the external leaf of the ectoderm), and even heart and bone marrow (derivative of the middle leaf of the mesoderm).