The black coat of the mouse refers to the genetically customized cells, the white is the non-modified cells. The scientists reproduce these animals to produce offspring which are 100% genetically modified, consisting of one half of CRISPR-Cas9. Credit: The Francis Crick Institute
Scientists at the Francis Crick Institute, in collaboration with University of Kent, have actually utilized gene editing innovation to produce female-only and male-only mice litters with 100% effectiveness.
This proof of principle study, released in Nature Communications today (Friday December 3rd, 2021), shows how the technology could be used to enhance animal welfare in clinical research study and perhaps likewise agriculture.
In clinical research and also farming, there is often a requirement for either male or female animals. For instance, laboratory research study into female or male recreation requires only animals of the sex being studied. And in farming, just female animals are needed for egg production and in dairy herds. This implies it prevails practice for animals of the unrequired sex to be culled after birth.
The researchers new technique uses a two-part genetic system to inactivate embryos quickly after fertilization, enabling just the wanted sex to establish. Such a genetically-based approach to control the sex of offspring could drastically reduce culling in both markets.
The embryo selection is based upon the truth that there are two components of CRISPR-Cas9– the Cas9 enzyme that cuts the DNA, enabling researchers to modify particular areas, and the guide RNA which brings the Cas9 to the right place on the genome. The group put one aspect of the system on the fathers X or Y chromosome, meaning that it will just be inherited by male or female embryos respectively. The other element is contributed by the mom, and is inherited by all embryos.
They targeted the Top1 gene, which is vital to DNA duplication and repair. When an embryo formed from a sperm and egg, each including one half of CRISPR-Cas9, the gene-editing was triggered in the embryo and it was unable to establish beyond a really early stage of around 16 to 32 cells.
Using this technique, the scientists were able to control, with 100% effect, the sex of a litter. To produce a male-only litter, the researchers edited the dads X chromosome, indicating only females inherited the unhealthy mutation, and for a female-only litter, they modified the Y chromosome.
Surprisingly, the approach did not cause a 50% decrease in the number of offspring produced, rather the litter sizes were in between 61%– 72% of the control litters. The scientists suggest this is because animals such as mice produce more eggs than needed during each ovarian cycle, enabling for a percentage of them to be lost during early advancement without reducing litter size. This implies that in situations where one sex is needed, fewer breeding animals will be needed in order to produce the same variety of the preferred sex of offspring.
As the Top1 gene is well conserved across mammals, these results may likewise apply to other animals.
Charlotte Douglas, first author and former PhD trainee and postdoctoral researcher at the Crick, says: “This approach works as we split the genome editing procedure in half, between a male and female, and it is only when the two halves satisfy in an embryo through breeding, that it is triggered. Embryos with both halves can not develop beyond very early cell stages.
” Weve also shown this procedure works effectively in various mixes– presenting either the Cas9 or the guide RNA components on to the moms or daddys chromosomes.”
As the offspring which endure just include half of the CRISPR-Cas9 aspects within their genome, this acts as a control avoiding the sex-selection being given to further generations, unless they are selectively reproduced with an individual of the opposite sex containing the other half. This is different to hereditary engineering through gene-drive techniques, which look for to spread a genetic anomaly extensively among a population.
There are also no harmful results of the gene edit in the enduring offspring.
James Turner, author and group leader of the Sex Chromosome Biology Laboratory at the Crick states: “This work might have valuable and immediate impact in scientific labs, as weve demonstrated how it is safe and efficient in mice, a typical mammal used in medical and clinical research. While a great deal of research requires both sexes, there are areas of study where just one is required. For example, when studying the reproductive system, sex-specific illness, or specific hormonal agents.”
Peter Ellis, author and senior lecturer in molecular genes and reproduction at University of Kent, states: “The implications of this work are potentially significant when it pertains to improving animal well-being, but need to be thought about at regulatory and ethical levels.
” In particular, prior to any prospective use in agriculture, there would require to be extensive public conversation and dispute, in addition to changes to legislation. On the clinical side, there is also much work to be done over a number of years. Additional research study is needed, first to establish the specific gene editing toolkits for different species, and then to check they are efficient and safe.”
Reference: “CRISPR-Cas9 effectors assist in generation of sex-specific phenotypes and single-sex litters” 3 December 2021, Nature Communications.DOI: 10.1038/ s41467-021-27227-2.
The scientists reproduce these animals to produce offspring which are 100% genetically customized, containing one half of CRISPR-Cas9. In clinical research study and also farming, there is often a need for either male or female animals. Laboratory research into female or male reproduction needs only animals of the sex being studied. And in farming, just female animals are required for egg production and in dairy herds. The researchers recommend this is because animals such as mice produce more eggs than needed during each ovarian cycle, enabling for a proportion of them to be lost during early development without reducing litter size.