Time：2023-04-01 13:20:51 source：psychiatricethics.com author：Mental disorder Read：480次

Artificial sperm to keep men away

In 2009, Professor Karim Nayenya of Newcastle University in the United Kingdom announced the creation of the first human sperm. The news once again brings to the fore a question about human reproduction: Can a woman have children without a man?

Artificial sperm and female sperm

Karim et al. first extracted male embryonic stem cells with XY chromosomes as "seeds", and placed retinoic acid and its In a solution of derivatives, they are converted into germline stem cells, which are then cultured into spermatogonial stem cells. The spermatogonial stem cells are then converted into spermatocytes with only 23 chromosomes, which are further cultured to form identifiable sperm cells. These artificial sperm appear to have some characteristics of sperm, such as certain protein forms that are unique to sperm, and one of the proteins in the tail is essential for the division of the egg; there is a tail and a head, which can be clearly seen under the microscope Swim with a wagging tail. Karim said this is a collection of "fully mature, functional" sperm that can fuse with human egg cells and eventually develop into embryos. This achievement means that there are new ways to help infertile patients, and even fundamentally change the way human beings reproduce, that is, they can reproduce without a man. For example, male germ cell sperm is not needed, but male skin cells are extracted, implanted with 4 genes, and the genes of the cells are rearranged to become skin stem cells with embryonic stem cell functions, which can be induced to differentiate into a variety of cells, including sperm. Of course, if the research goes well, it may be possible to extract female embryonic stem cells, bone marrow stem cells or skin cells in the future, induce differentiation into sperm, and then use such sperm to combine with eggs to reproduce humans. However, for now this is just an idea. In January 2008, Karim took stem cells from the bone marrow of female donors, hoping to use the same method to convert them into sperm, but so far has not been successful.

Whether it is really "sperm", it still needs to be verified

Even if sperm are cultured with embryonic stem cells, but such sperm is true or false, and has the function of sperm , or is it just a fake sperm? Achim Sulani, a professor of physiology and reproduction at the University of Cambridge in the United Kingdom, believes that the sperms cultured by Karim are just "sperm-like cells", "there is still a long way to go to become real sperm cells. ". The turning on of genes in embryos is linked to methyl groups. A large number of studies have found that DNA methylation can cause changes in chromatin structure, DNA conformation, DNA stability and the way DNA interacts with proteins, thereby controlling gene expression. DNA methylation can cause gene inactivation. As early as more than two years ago, Karim's research group used male mouse embryonic stem cells to grow mouse sperm. In order to verify whether these sperm have real sperm function, Karim and others injected these sperm into eggs, cultivated them into embryos, and then implanted the embryos into surrogate female mice. The mice later all died. The researchers speculate that the methyl groups in the artificial sperm may block the expression of some key genes, causing the mice to die. In addition, even if artificial sperm is cultivated and has normal 23 chromosomes after meiosis, it is not a sperm with normal function. Because normal sperm have some genes that help them complete their normal functions - dynein, if the artificial sperm does not have this gene or the gene is inactivated, the tail of the sperm cannot be bent, so it cannot allow the sperm to swim normally. egg union. In addition, there is a recognition protein on the surface plasma membrane of sperm and egg. If the recognition protein of either side is missing or abnormal, sperm and egg will meet but not know each other, and pregnancy will not be possible. The artificial sperm created by Karim et al. may not have the function of normal sperm for the above reasons. The only way is to use insemination experiments to verify its normal function. And the success rate of breeding test-tube mice with artificial sperm is extremely low. Karim's team produced only seven pups out of about 400 fertilized eggs. Moreover, the survival time of these young mice is extremely short. One of the pups died soon after birth, and the remaining 6 died after 5 months, while the average lifespan of normal mice is about 2 years. As a corollary, even if Karim's team produced human test-tube sperm that could produce offspring, they would likely not live long.

No sperm will work

Although many experts have expressed great doubts about artificial sperm, and previous research of artificial sperm is not safe, but that doesn't mean the research done at Newcastle University is meaningless. On the contrary, many researchers believe that the exploration of the sperm production process will help to understand the secrets of sperm function and function loss, and thus help to treat male infertility. Before Karim, there were more studies trying to prove that it is possible to have offspring by bypassing male (male) sex. Cloning (asexual reproduction) is a typical method, but this method failed to clone Dolly the sheep. was generally opposed. Since then, Japanese researchers have published an article in the British "Nature" magazine saying that they did not use the eggs of two female mice but gave birth to a normal offspring, named Moon Goddess. Dolly is not exactly the same as the parthenogenesis of the Moon Goddess. Dolly was conceived by implanting the nucleus of one ewe's mammary gland into the nucleus of another ewe's egg, while the Moon Goddess was created by the fusion of two different eggs. The study used 598 mouse eggs to create enough embryos to grow, which were then implanted in 26 female mice, and 24 of them became pregnant. As a result, only two mice were delivered, and only one was a normal pup, the moon goddess. Leaving aside the ethical and legal issues, the offspring produced by this technique, like Dolly, are full of multiple genetic defects, age prematurely and die prematurely (Dolly was euthanized for a variety of terminal and intractable illnesses). ). So, what is the use of life produced by such technology? Of course, parthenogenesis has other meanings. For example, it is possible to explore why humans and higher animals are bisexual rather than parthenogenetic, and perhaps this can solve many mysteries in the history of biological evolution and some diseases. However, this is by no means the reason why the world does not need men.

(责任编辑：Anxiety disorder)

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