Gene-editing technology is used to create female-only and male-only mice litters – in breakthrough that could improve animal welfare in scientific research 

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  • Often only one sex is needed for the study of fertility, hormones, and certain diseases.
  • Similarly, male animals do not lay eggs and are often unwanted for their meat.
  • As a result, animals of the other sex are often killed after birth in these settings.
  • This new application of CRISPR-Cas9 gene editing may reduce the need for
  • It works by inactivating the embryo of the unwanted sex soon after fertilization
  • The Francis Crick Institute-led team said it was 100 percent effective

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Single-sex litters of mice containing only female or male pups have been produced through the so-called CRISPR-Cas9 gene editing technique.

The technique, developed by experts at the Francis Crick Institute and the University of Kent, works by inactivating an embryo of one penis shortly after fertilization.

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It can be used to improve animal welfare in both laboratory and agricultural settings, where only female or male animals are needed for a variety of reasons.

It is common for animals of the unviable sex to be killed – a practice that can be significantly reduced by controlling the sex of the animals before birth.

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Genetic modification of both parents is required for the technique to work, however, this approach would not be suitable for forcing the sex of the designer babies.

Single-sex litters of mice – which include only female or male pups – have been produced through the so-called CRISPR-Cas9 gene editing technique. Image: Mice that were bred to produce single-sex litters. The dark parts of their coat are due to genetically modified cells, while the white parts come from non-modified parts of their genome.

The technique, developed by experts at the Francis Crick Institute and the University of Kent, works by inactivating an embryo of one penis shortly after fertilization.

The technique, developed by experts at the Francis Crick Institute and the University of Kent, works by inactivating an embryo of one penis shortly after fertilization.

When are only female or only male rats needed?

It is not uncommon for animals of only one sex to be needed in both scientific research and farming.

Paper author and Francis Crick Institute and geneticist James Turner explains: ‘Although a lot of research is needed for both sexes, there are areas of study where only one is needed.

‘For example, when studying the reproductive system, gender-specific diseases, or certain hormones.’

Meanwhile, farmers often only need female animals. These – unlike their male counterparts – are the ones that lay eggs, produce milk and produce more flavorful meat.

Unnecessary sex is common in both settings – a practice that can be significantly reduced by using CRISPR-Cas-9 to control the sex of the animal before birth.

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The technology, developed by Francis Crick Institute geneticist Charlotte Douglas and her colleagues, works by taking advantage of two parts of the CRISPR-Cas9 gene editing tool.

The first is Cas9 – an enzyme that cuts DNA – while the second is the ‘guide RNA’ that cleaves Cas9 to the correct location on the target genome, allowing the gene to be inserted, removed or changed at the desired point.

In their proof-of-principle study, the researchers placed one of these two elements on the earliest father mouse’s X or Y chromosome – meaning it would only be inherited by their female or male embryos, respectively.

The other gene editing element was contributed by the mother mouse’s X chromosomes – meaning it was inherited by all embryos.

“This method works because we split the genome editing process between male and female in half, and it is only active when the two halves meet in an embryo through reproduction,” Douglas said.

The team targeted CRISPR-Cas9 elements on the so-called Top1 gene, which is essential for DNA replication and repair.

Accordingly, Dr Douglas explained, ‘an embryo with both halves cannot develop beyond the very early cell stages.’

Notably, embryos of the target sex – which have been given the deleterious mutation – fail to multiply beyond dividing into approximately 16 to 32 cells.

“We have also shown that this process works successfully in various combinations – introducing either Cas9 or guide RNA elements onto the mother’s or father’s chromosomes,” the researcher said.

The team reports that the approach is 100 percent successful and causes no harmful effects in live fetuses, although, perhaps somewhat counterintuitively, it does not result in a 50 percent smaller birth weight.

Instead, the team found that genetically altered litters ranged from 61–72 percent of the size of control litters that were produced without any editing.

According to Dr. Douglas and colleagues, this is because rats are among the animals that produce more eggs than necessary during each ovarian cycle – allowing some to be lost during early development without cutting down on litter size. gives.

Regardless, this boost means that, should gene editing technology be implemented, animals with low fertility may be required to produce the same number of offspring of the desired sex.

The technology works by taking advantage of two parts of the CRISPR-Cas9 gene editing tool.  The first is Cas9 – an enzyme that cuts DNA – while the second is the 'guide RNA' that cleaves Cas9 to the correct location on the target genome, allowing the gene to be inserted, removed or changed at the desired point.  Shown: CRISPR-Cas9 in operation

The technology works by taking advantage of two parts of the CRISPR-Cas9 gene editing tool. The first is Cas9 – an enzyme that cuts DNA – while the second is the ‘guide RNA’ that cleaves Cas9 to the correct location on the target genome, allowing the gene to be inserted, removed or changed at the desired point. Shown: CRISPR-Cas9 in operation

If surviving offspring are required to reproduce, they harbor only a portion of the CRISPR-Cas9 elements within their genome—meaning that sex selection would not naturally be passed on to the next generation.

(However, the researchers noted, the element can be activated by selectively breeding opposite-sex animals with the second half of the gene editing tool.)

In this way, the technique differs from a ‘gene-drive’ approach to genetic engineering – as, for example, there are…

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