On August 26, the international academic journal "Science" published a pioneering achievement of Chinese scientists online - the team of researcher Li Wei and Zhou Qi of the Institute of Zoology, Chinese Academy of Sciences, Beijing Institute of Stem Cell and Regenerative Medicine, and the team of researcher Zhou Qi, which is the first in the world. Programmable joining of complete mammalian chromosomes and creation of mice with novel karyotypes (karyotypes).

Some commentators believe that this work represents another breakthrough in bioengineering technology, and has opened up a "building knowledge" for in-depth understanding of the molecular mechanism of structural variation such as large-scale remodeling of mammalian chromosomes on their growth and development, reproduction and evolution, and even speciation. Synthetic biology research strategy, and established the corresponding technology platform.

First complete chromosomal rearrangement in mammals

To understand this achievement, we must first understand a concept - chromosomal rearrangement. Li Wei introduced that chromosomal rearrangement refers to the breaking of chromosomes and connecting with other chromosomes to form new chromosomes.

In the long process of biological evolution, chromosomal rearrangement is an important factor that leads to qualitative changes and leaps in living things. But for individuals, chromosomal rearrangements are more of a disease — some types of childhood leukemia, infertility, and other diseases are caused by chromosomal rearrangements.

Understanding the mystery of chromosomal rearrangement can further reveal the mystery of human evolution, and can also make a leap in the treatment of various diseases. Therefore, chromosomal rearrangements have become a focal area of research for biologists. In recent years, precise chromosomal rearrangement has been the first to succeed in yeast with a simple and haploid genome. But because mammalian genomes are much more complex than yeast genomes, complete chromosomal rearrangements in mammals have not been successfully achieved.

After years of hard work, Chinese scientists have achieved complete chromosomal rearrangement in mammals for the first time in the world, making a new breakthrough in synthetic biology. "Our study breaks the technical bottleneck, using mouse haploid embryonic stem cells and CRISPR gene editing tools to successfully connect the longest chromosomes 1 and 2 forward and reverse, and the medium length chromosomes 5 and 4. End-to-end connection was performed, and it was found that chromosome breakage and reconnection may occur during the process of chromosome connection." Li Wei said, "The results show that two independent chromosomes from mice can be genetically edited and can be non-homologous. The end joining repair method joins into one chromosome."

Will have a huge impact on understanding evolution, designing life, treating diseases, and more

On this basis, the researchers further studied the impact of specific chromosomal rearrangement linkages.

First, the researchers confirmed that longer chromosomes in mammalian cells are not always better. Too long can cause abnormal cell division. Li Wei introduced that at the cell phenotype level, the pluripotency gene expression and differentiation of stem cells did not change significantly after chromosome connection, while the haploid stem cells with the longest chromosome connection (chromosome 2 and chromosome 1 connection) were diploid The rate is significantly accelerated, and spontaneous polyploidy still occurs in embryonic stem cells and neural stem cells that have become diploid. "This phenomenon is caused by abnormal cell division due to excessive chromosome length, and it also proves that there is a certain limit to the chromosome length of mammalian cells. For mouse cells, the upper limit of chromosome length is between 308.3Mb and 377.6Mb. "

Second, the researchers "created" mice with new and unique karyotypes. Li Wei introduced that in order to answer the impact of specific chromosomal rearrangements on the phenotype of animals, the researchers successfully obtained chromosomally connected mice by injecting haploid stem cells into oocytes - it seems to be similar to ordinary mice. No difference, in fact, it has a new and unique karyotype that the world has never existed.

The study found that different chromosome junctions had different effects on mice. The longest chromosomal junction (the junction of chromosomes 2 and 1) prevented embryonic development from proceeding normally; after the junction of chromosomes 1 and 2, chromosome 1 The breakage and reconnection of chromosome 17 produced mice that exhibited abnormal growth curves and behavior; mice with junctions of chromosomes 4 and 5 showed no apparent abnormalities.

At the same time, the linked chromosomes can also be passed on to offspring, and further mating can produce homozygous mice. Li Wei said: "This proves that the connection of two chromosomes does not lead to absolute reproductive isolation, but the fertility of mice carrying the connected chromosomes is significantly reduced. Further exploration found that although the connected chromosomes can still be separated from the two Homologous chromosomes undergo normal synapsis, but the segregation of homologous chromosomes after synapsis is abnormal."

Finally, the researchers also comprehensively analyzed the changing trend of chromosome spatial structure in embryonic stem cells, neural stem cells and brain. The study found that changes in the spatial structure of chromosomes weakened with differentiation.

Li Wei said that this research strictly abides by our country's laws and regulations and relevant state regulations, and conforms to our country's and international ethical standards. "Our study establishes for the first time a new technology for programmable connection of complete chromosomes in mammals, enabling the editing of very large-scale genomes, adding a new research tool to mammalian synthetic biology. Mammalian synthetic biology provides an important reference for chromosomal design and synthesis; by reconstructing chromosomal rearrangement events in laboratory mouse models, it helps to understand evolutionary-derived chromosomal fusions, and also demonstrates the relevance of chromosomal rearrangements to reproductive isolation, It provides a new idea for evolutionary biology research. And the precise chromosome rearrangement technology provides an animal model for the establishment of chromosomal rearrangement diseases, the study of the pathogenesis of infertility and tumors caused by chromosomal rearrangement, and the exploration of the treatment of diseases. new technological means.”

(Original title "My scientist opens up a new field of mammalian chromosome editing and realizes the first global programmable connection of complete mammalian chromosomes")