Scientists at the Francis Crick Institute and the University of Kent used the gene editing technology CRISPR/Cas9 to create female-only and male-only mice litters. The findings, published in Nature Communications, could provide a genetic solution for the male chick layer dilemma.
“We have developed a method for 100% efficient sex selection of offspring sex in mice, and we believe this will be readily adaptable to other species including livestock, should public opinion and legislation allow for the use of this type of genetic technology in the food chain,” Peter Ellis, co-author of the paper and senior lecturer in molecular genetics and reproduction at University of Kent, explained to WATTPoultry.com.
In mammals, the father passes the Y chromosome to his sons and the X chromosome to daughters. The approach uses a two-part genetic system that inactivates embryos shortly after fertilization, allowing the growth of only the desired sex.
“The father carries one part - in this case the CAS9 enzyme - either on his X or his Y chromosome so it is only passed to one sex of offspring. This is then triggered by a second gene - the guide RNA - inherited from the mother. When the two elements are combined in the next generation, the CAS9 and guide RNA act together to disable a gene called Top1. This prevents the embryos from developing beyond a very early stage,” Ellis continued.
Potential solution for the layer industry?
Approximately 6-7 billion male layer chicks are culled each year, a major animal welfare and economic concern for the layer industry. Producers spend more than $70 million in labor and energy to incubate and sex these eggs and the value of wasted eggs in the U.S. is more than $440 million annually.
Animal welfare organizations have pressured the egg industry to find an alternative approach.
However, there are currently several barriers to using gene editing in poultry. Birds require a different gene editing approach than the one used in mammals. For mammals, a technique called somatic cell nucleic transfer (SCNT) is used, but it requires access to the developing embryo.
Instead, the process used for avian species makes genetic edits to primordial germ cells, the progenitors for sperm and ovum cells in the chicken.
“As a very loose guideline, designing and demonstrating the principle in laboratory mice has taken six years of work up till now, much of it in cell line work. A similar time frame would be required for proof of concept in a farm species, followed by a further scale-up period before it could be deployed widely,” said Ellis. “The mechanics of sex chromosome expression and silencing are different between poultry and mammals, so this is an area where cell line work will be needed prior to any in vivo work.”
Nonetheless, this is an exciting finding that could one day have important implications for the poultry industry.