On June 21 this year, Professor Ding Sheng's team from the School of Pharmacy of Tsinghua University published a paper entitled "Inducing Mouse Totipotent Stem Cells Using Specific Chemical Cocktails" in the international academic journal Nature, showing that instead of using fertile cell sperm and egg combination to form fertilized eggs and two-cell embryos (totipotent stem cells), some cells are modified to have great potential to create new life. This finding could rewrite people's perceptions of life and the processes by which life arises.
So, what is the specific content of this new discovery of Ding Sheng's team? Compared with the work of predecessors in this field, where is the breakthrough point? We invited Zhang Tiankan, a well-known popular science author, to make a detailed interpretation of related issues.
Cloning techniques do not require amphoteric reproduction to create new life, but still rely on germ cell eggs
The essence of Ding Sheng's team's new discovery is to find a new way to reverse life, and to understand the breakthrough significance of Ding Sheng's team's new discovery, let's start with the history of this field.
Germ cells are a general term for cells in multicellular organisms that can reproduce offspring, including germ cells (sperm and egg cells) that have finally differentiated from the original germ cells to the end. The term was coined by A. Engler and K. Plantar in 1897 to distinguish it from somatic cells. Somatic cells eventually die, and only germ cells have a chance to survive to the next generation.
We know that mammals, including humans, reproduce and reproduce by both sexes, and combine sperm and eggs from germ cells to form single-cell fertilized eggs, then two-cell embryos (totipotent stem cells), followed by 4 cells, 8 cells... Embryos (stem cells) develop into the inner, middle and outer germ layers, and form various organs, tissues, muscles, bones, nerves, and brains, producing a complete life.
In the 1960s, British scientist John Gordon invented cell nuclear transplantation techniques in his research on laurels. In 1997, Wilmut further used this technique to breed the cloned sheep Dolly.
This method is to extract the nucleus of the adult cell, implant it into an egg cell that removes the nucleus, reorganize it into an egg, and then stimulate the recombinant egg to differentiate and develop with an electric pulse to form an embryo, thereby giving birth to a new life.
The main genetic information for the cloned sheep Dolly comes from the Finnish Dorset female sheep. Breast cells (a type of somatic cell) are removed from the mammary gland of a Finnish Dorset mother sheep, placed in a low concentration of nutrient culture, and the cells stop dividing and enter a quiescent state, which is called a donor cell. The nuclei of the unfertilized egg cells of a black-faced Scottish ewe are removed, called recipient cells. The nuclei of the breast cells of the previously treated Dorset mother sheep are then extracted, implanted in the egg cells that remove the nucleus, and cell fusion is carried out with electrical stimulation to form a differentiatable and developable embryo. The embryos are then transferred to the womb of another black-faced Scottish ewe for further differentiation and development, and finally dolly is born. Dolly has exactly the same appearance as dorset ewes.
The production of cloned sheep Dolly does not require amphoteric reproduction, without the participation of germ cell sperm, but still needs egg cells as germ cells. So people say that with cloning technology, mammals do not need male involvement in reproduction, only specific somatic cells and female egg cells.
The 2012 Nobel Prize results and subsequent research findings were induced multipotent stem cells
Japan's Shinya Yamanaka won the 2012 Nobel Prize in Physiology or Medicine with John Gordon of the United Kingdom for discovering induced multipotent stem cells.
In 2006, Shinya Yamanaka's group used retroviral vectors to transfer four genes, Oct4, Sox2, Klf4, and c-Myc, into adult cells in mice, reprogramming these cells to produce characteristics similar to mouse embryonic stem cells, which are induced multipotent stem cells.
In 2007, Kazutoshi Takahashi's team in Japan used four genes, Oct3/4, Sox2, Klf4, and c-Myc, to induce adult dermal fibroblasts to produce human-induced multipotent stem cells. Human induced pluripotent stem cells are similar to human embryonic stem cells in terms of morphology, proliferation, surface antigens, gene expression, epigenetic status of pluripotent cell-specific genes, and telomerase activity. Human-induced pluripotent stem cells can also differentiate into three germ layer cell types in vitro and teratomas.
In 2013, The research team of Professor Deng Hongkui of Peking University published the results of the research in the journal Science, using a new approach, that is, exogenous chemical small molecule compounds to reprogram mouse somatic cells into chemically induced multi-potential stem cells, which also reversed cell fate. Of course, there are many chemical molecules used, with seven small molecule compounds capable of generating chemically induced multipotent stem cells from mouse somatic cells at up to 0.2% frequency. These cells are similar to embryonic stem cells in terms of gene expression profile, epigenetic status, and potential for differentiation and germline transmission.
On April 13, 2022, Deng Hongkui's research team published a research paper in the journal Nature, demonstrating that human adult cells can be induced into multi-potential stem cells using chemical induction.
These studies have shown that adult cells, whether in mice or humans, have the potential to generate multipotent stem cells through biological and chemical inducing factors, which may produce various organs and tissues, and may even develop into living individuals.
Here we have to explain some concepts. The so-called stem cell (stem cell) "stem", meaning "stem", "origin", simply put, stem cells are a type of cells with unlimited or immortal self-renewal ability, is able to produce at least one type of highly differentiated daughter cells.
According to functional criteria, stem cells can be divided into 5 categories.
One is totipotent stem cells (from a combination of sperm and egg), which can differentiate into embryos and extra embryonic tissues such as chorionic, yolk sac, amniotic membrane and allicure. In humans and other embryonic organisms, these extraembical tissues can form a placenta. Totipotent stem cells can produce a fully functional individual.
The second is multipotent stem cells (also known as universal stem cells), which differentiate in about 4 days after the development of the fertilized egg, and they can self-propagate and differentiate into one of three germ layers (ectoderm, mesoderm and endoderm). These three germ layers can further differentiate into all tissues and organs in the human body.
The third is pluripotent stem cells, which can differentiate into osteoblasts, muscle cells, fat cells and chondrocytes.
The fourth is oligopotent stem cells, which are similar to pluripotent stem cells, but their differentiation ability is limited, and they can only develop into closely related cell types, such as hematopoietic stem cells and endodermal stem cells.
Fifth, monotent stem cells, which are the stem cells with the most limited differentiation, such as muscle stem cells, which can only differentiate into muscle cell types.
From here, we can know that the work of Shinya Yamanaka and later researchers, compared with cloning technology, has shed its dependence on germ cell egg cells, but whether it is induced by genes or chemical induction, the induced stem cells are multi-potential stem cells, not all-round stem cells with the highest functional standards.
Ding Sheng's team induced the production of stem cells, the highest level of stem cells or the origin of life, the totempotent stem cells
Speaking of this, we can finally better understand the work of Ding Sheng's team this time.
On June 21, Ding Sheng's team published a paper entitled "Inducing Mouse Totipotent Stem Cells Using Specific Chemical Cocktails" in the international academic journal Nature. In this study, Ding Sheng's team used a "cocktail" drug composed of three chemical molecules TTNPB, 1-Azakenpaullone, and WS6 (TAW) to induce mouse pluripotent stem cells into totipotent stem cells with the potential to transform into intact organisms, and to maintain the totipotent types (intra-embryonic and extraocularular differentiation potential) of these induced cells in the laboratory. This means that such cells can either develop into a complete living individual or into various organs and tissues, such as livers, bones, nerves, etc.
The research team named these cells chemically induced totipotent stem cells (also known as TAW-induced totipotent stem cells, or TAW cells or induced totipotent stem cells). These cells resemble two-cell embryos developed from the initial fertilized egg cells at the transcriptome, epigenomic, and metabolome levels.
The key to this study was that the team selected and screened thousands of small molecules to determine three small molecule combinations — TTNPB, 1-Azakenpaullone, and WS6 (TAW). TTNPB is a tretinoin receptor agonist, which is a necessary substance to induce cellular totipotency; 1-Azakenpaullone is a highly selective inhibitor that inhibits the side effects of TTNPB in long-term culture and promotes the self-renewal of totipotent stem cells; WS6 molecules can promote and maintain the stability of totipotent stem cells.
After that, the research team tested the differentiation potential of TAW cells in vitro and injected them into mouse early embryos to observe the differentiation potential in vivo. The results showed that these cells not only showed the characteristics of true totipotent stem cells in the dish, but also in vivo could differentiate into intraembryonic and extraembryonic lineages, with the potential to develop into fetuses and surrounding yolk sacs and placenta, which is a typical feature of ordinary totipotent stem cells.
The researchers also found in the transcriptome, epidermal group, and metabolome that hundreds of genes commonly found in totipotent stem cells in TAW cells were turned on, and genes associated with pluripotent stem cells were silent in the cells, and the overall situation was very similar to that of totipotent stem cells.
These results suggest that higher organisms may not be the only one that must combine reproductive cells of both sexes to reproduce, and that other ways can reproduce. In the future, TAW cells may develop into living individuals in vivo or in vitro ( such as in a specific vessel or artificial uterus .
As described on the official website of Tsinghua University: "In the future, not only like the hairs on Sun Wukong's body in the novel, but also any somatic cell such as blood and skin on the animal can be reprogrammed into pluripotent stem cells, and then 'medicated' to become all-round stem cells that can independently form life." "Here we also need to see that according to the technology provided by The current Ding Sheng team, multi-functional stem cells are needed in the hair follicles of the plucked hair, and it is necessary to induce the development of omnipotent stem cells through the TAW cocktail, and then develop from the omnipotent stem cells into living individuals."
The breakthrough of the new discovery is significant
Earlier we talked about the work of Shinya Yamanaka, who won the 2012 Nobel Prize in Physiology or Medicine, and also talked about the work of the research team that followed, including the Chinese scientist Deng Hongkui. So, where are the differences and breakthroughs that Ding Sheng's team found this time?
Compared with the previous research mentioned above, the research of Ding Sheng's team is that the technical route adopted is different. Ding Sheng's team used chemical (TAW cocktail) induction, while japanese researchers used biological factors (4 genes) induction, although Deng Hongkui's team also used chemical factor induction, but the chemical factors are different.
More importantly, What Ding Sheng's team obtained was induced totipotent stem cells, which are the highest level of stem cells, which may be conceived into living individuals, and more likely to differentiate and develop into various tissues and organs; The Japanese researchers and Deng Hongkui's team obtained induced multi-potential stem cells, which are secondary stem cells that can develop into various tissues and organs, and theoretically can also give birth to individual life, but they are less likely than totipotent stem cells to conceive into living individuals.
Now, the totem stem cells created by Ding Sheng's team are also reversing life, that is, reversing the pluripotent stem cells of mice into totipotent stem cells, which can theoretically produce both new life individuals and various organ tissues.
The significance of this research lies in the fact that one is a new understanding of the origin and process of life, and living individuals can not start from germ cells, but by reversing or cultivating pluripotent stem cells into totipotent stem cells to conceive life.
Secondly, through such a way and process, a variety of organs, such as the heart, liver, kidney, etc., can be cultivated in such a way and process to solve the problem of lack of donor organs that has been difficult to solve in organ transplantation.
Compared with the cloning method of cloning sheep Dolly, cloning technology can also reproduce without sexual reproduction, but this process still needs to rely on germ cell eggs. The totem stem cells created by Ding Sheng's team only need a "magic potion" to be reversed from pluripotent stem cells, and no longer need the participation of germ cell eggs. In this sense, in the future, as long as pluripotent stem cells or adult cells of a certain species are obtained, new life can be created.
As Ding Sheng said, this research creates the possibility of recreating individual life and even accelerating the evolution of different species, marking the opening of a new field of life creation research and is a "holy grail" in the field of biology.
Of course, it must be pointed out that the importance of such research in the study of life and the treatment of diseases is unquestionable, but if new life is to be created through this technology, many ethical and legal issues need to be solved. From the practice of animal cloning, it is feasible to reproduce animal offspring without the cloning technique of gender reproduction, so it seems that there is also a lot of room for development and research using this new technology to create new life in animals.
However, the international community has always had a strict ban on human cloning, and if someone wants to use the new technology of Ding Sheng's team to create a new human life, it will certainly not work ethically and legally. As Professor Ding Sheng put it, the "many possibilities" brought about by this discovery will cause controversy in scientific topics, especially the discussion of social morality and ethics. "Over the past decade, the scientific community has not seen any more lenient restrictions on human embryo research." Ding Sheng said that their thesis research process strictly follows the scientific ethical framework.
Source: Beijing Daily Client
