Perspectives on reduced methane production in dairy cattle using gene-edited induced pluripotent stem cells (iPSCs)
The increasing demand for animal origin products is a consequence of the world’s population expansion, and dairy cattle are of great importance since milk is an excellent source of proteins, high-quality fat, minerals and vitamins.
To supply the increasing food demand, it is necessary to improve the production efficiency associated with reducing unfavorable effects on the environment, such as greenhouse gas emissions (GHG).
Animal genetics can be notably used to reduce methane production in cattle due to its influences on the ruminal microbiome composition.
Implementing strategies to reduce methane emissions in dairy cattle could benefit the environment and the economy.
The rumen microbiome comprises bacteria, ciliary protozoa, anaerobic fungi, and archaea, which are the essential microorganisms in methane (CH4) production from byproducts (H+) of the digestion of the other microorganisms. Indeed, one of the digestive fermentation products is methane, which is released through eructations and flatulence.
The methane is colorless, odorless and its contribution to global warming is 25 times greater than carbon dioxide (CO2). Also, it represents 5-7% of energy loss from dairy cows in standard diets, negatively affecting animal production .
Therefore, implementing strategies to reduce methane emissions in dairy cattle could benefit the environment and the economy. Although most of the variation in methane production is due to non-genetic factors (such as feed and handling), the animal genetics can be notably used to reduce methane production in cattle due to its influences on the ruminal microbiome composition.
Such genetic influence is a polygenic characteristic, and the most influential genes for CH4 production have been reported, enabling the use of biotechnologies to assist in the production of sustainable dairy cattle .
Among the possible biotechnologies, pluripotent stem cells (PSCs) have significant advantages, as they can differentiate into cells of the three embryonic layers (endoderm, ectoderm, and mesoderm).
In particular, they can contribute to the development of embryos and even gametes in vitro.
Nevertheless, the isolation of embryonic stem cells (ESCs) leads to ethical concerns.
Additionally, pluripotency is still not robustly maintained in vitro. The possibility to reprogram somatic cells to the state of pluripotency (induced pluripotent stem cells – iPSCs) leads to a new era where pluripotency was achieved in vitro with no ethical issues involved with embryo destruction.
Moreover, adult cells can be reprogrammed in vitro, an outstanding achievement once genotype and phenotypes of the target animal are already known .
Thus, with the use of iPSCs, gene editing can be performed using technologies such as the CRISPR/Cas9 tool to knock-down or –out  the genes relevant to high methane production, enabling to decrease the methane production of an animal with high production potential.
Such edited iPSCs will enable the generation of clones through nuclear somatic cell transfer (SCNT), or even, in the near future, the generation of viable gametes in vitro [5,6], which will not only contribute to the production of animals presenting less methane production but will also contribute to the maintain the genetic diversity, to reduce the interval of generations among populations, therefore reducing the time and costs required to obtain a genetically superior herd.
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