However, there are still many puzzles in the process of sperm formation. Gene mutation and abnormal gene expression are more important reasons for male infertility.
Recently, Liu Mofang's research team of Center for Excellence and Innovation of Molecular Cell Science (Institute of Biochemistry and Cell Biology) of China Academy of Sciences, Huang Gang's research team of Xinhua Hospital affiliated to Shanghai Jiaotong University School of Medicine and many laboratories at home and abroad found that RNA binding protein FXR 1 can activate the translation of mRNA in mouse sperm cells in the middle and late stages through liquid-liquid separation, thus ensuring the normal sperm formation process. This achievement was published online in the international academic journal Science in the early morning of August 12, Beijing time.
This scientific achievement was published in the journal Science. Photo courtesy of Center for Excellence and Innovation in Molecular Cell Science, China Academy of Sciences.
Professor Martine Simonelig of the French Institute of Human Genetics pointed out in the outlook commentary attached to the journal, "This study has discovered a new function of aggregation and translation activation of biomolecules, and further revealed the importance of FXR 1 phase separation ability to mouse spermatogenesis."
In the process of sperm cell deformation, with the gradual compression of the nucleus, the transcription activity of the genome will gradually decrease until it stops completely. Genes needed for sperm cell development in the later stage need to be transcribed into messenger ribonucleic acid (mRNA) in advance, and then preserved in a state of near "dormancy" in translation inhibition, and then the translation is reactivated at a specific development stage, so that protein can be synthesized to function. However, scientists still know little about how mRNA stored in these late sperm cells is activated through translation.
The research team conducted this study with mice as model animals. It was found that an RNA binding protein FXR 1 was highly expressed in mouse testis and later appeared in protein translation machine of sperm cells.
After the Fxr 1 gene was knocked out in germ cells, the translation activity of mRNA bound to FXR 1 in mouse testis decreased, and the protein expression decreased obviously. Mice showed azoospermia and male sterility.
Further research shows that FXR 1 interacts with many translation-related factors in sperm cells to form a dynamic droplet structure, which can recruit a large number of mRNA in vivo.
According to the existing theory, this droplet structure is usually that some biological macromolecules (such as protein or nucleic acid) reach a certain concentration in the cell, forming a membraneless subcellular organelle structure independent of the surrounding environment, so as to perform specific biochemical reactions or biological processes. The formation process is called liquid-liquid separation, which is common in eukaryotic cells. Subsequently, in vitro experiments proved that FXR 1 had remarkable liquid-liquid separation ability. The researchers speculate that FXR 1 may form the above droplet structure through liquid-liquid separation, and then participate in the translation activation process of mRNA.
In order to test this conjecture, the researchers tested the relationship between the ability of FXR 1 droplet formation and mRNA translation activity in cultured cells in vitro and sperm cells in vivo.
The results show that destroying the dripping ability of FXR 1 will lead to the decrease of mRNA translation activity. Subsequently, the researchers used CRISPR-Cas9 combined with semi-cloning technology to further mutate FXR 1 in mouse germ cells into FXR 1 variants that could not form droplets. It was found that the translation activity of mRNA in spermatogenic cells of mice decreased significantly, and mice showed azoospermia and male sterility.
This study reveals a new mechanism that FXR 1 liquid-liquid separation mediates mRNA translation activation in the late stage of mouse sperm cells, which is helpful to further understand the complex spermatogenesis process and provide theoretical basis for the diagnosis and treatment of male infertility.
Group photo of scientific research team
This study was jointly completed by Liu Mofang's research group and Huang Gang's research group from the Center of Excellence for Molecular Cells of Xinhua Hospital affiliated to Shanghai Jiaotong University School of Medicine. Dr. Kang, Ph.D., Ph.D. and Zhong Ai from Wuhan University, Dr. Li Qing from Xinhua Hospital and Dr. Yu Xinghai from Center of Excellence in Molecular Cells are the first authors of the thesis.
The research was assisted by Professor Fu Xiangdong from the University of California, San Diego, Professor Li and Professor Gou Lantao from the Center of Excellence in Molecular Cells, Professor Guo from Nanjing Medical University, Professor Shi Huijuan from Shanghai Institute of Family Planning Science and Professor David L. Nelson from Baylor Medical College. At the same time, it has been funded by the Ministry of Science and Technology, NSFC, China Academy of Sciences and Shanghai Science and Technology Commission, as well as GTP Center, molecular biology technology platform and cell analysis technology platform.