Sneha Singhal, Jaypee Institute of information technology, Noida
RIKEN researchers have developed the first genetically engineered marsupial at their Biosystem Dynamics Research (BDR) facility. In the world of marsupials, the grey short-tailed opossum (Monodelphis Domestica) is one of the few popularly studied laboratory animals. Researchers, who published their findings in Current Biology, are getting closer to understanding the genetics of traits that are unique to marsupials. In a successful experiment, they created opossums without Tyr at the Tyr locus after microinjecting pronuclear stage zygotes using the CRISPR/Cas9 genome editing system.
The likeness of the opossum to popular rodents:
Research on biological processes relies heavily on genetically modified animals, particularly mice and rats. Researcher’s frequently silence genes to elucidate how they function. Because marsupials possess unique characteristics, it is imperative to develop a representative model of them. It is believed that all marsupials descend from the opossum, which has been considered the ancestor of all mammals. As far as body size and breeding characteristics go, the opossum closely resembles popular rodent models, such as the mouse and rat.
Characteristics that make marsupials special:
The opossum, like other marsupials, has some specific characteristics that do not appear in other mammals. Studying marsupial biology has gained interest because of these characteristics:
- In the absence of a functional placenta, the embryo develops.
- Early pups birth occurs i.e., premature.
- Having the first complete genome sequenced in a marsupial.
- When exposed to ultraviolet light, it can develop skin cancer.
- An opossum pup with spinal cord injury can naturally heal itself.
It is still not possible to genetically modify them without using established technology. Researchers at RIKEN BDR are now using gene-editing technology to advance opossum research, led by Hiroshi Kiyonari.
Genome editing and embryo transfer technology:
Since the entire genome is edited by injecting a solution into the fertilized eggs, genome editing requires the systematic collection of fertilized eggs. A couple of opossums can’t mate for about a week even if they live together, due to their territoriality and long estrus cycles, which makes it difficult to proceed systematically with the experiment. To stimulate estrus in the females, the researchers administered a hormone commonly used in mice and other laboratory animals, which lead to significant reductions in the mating time.
A fine needle is generally used to inject the solution needed for genome editing into a fertilized egg. Opossums’ fertilized eggs are enveloped in a thick layer of proteins covered in a hard shell, so the injection needle cannot penetrate them. Kiyonari explained that the needle was combined with a piezoelectric element to penetrate. The piezo injector allows zygotes to be injected with minimal harm to the zygotes.
The study:
Scientists examined a gene responsible for making body pigments as a means of confirming their overall methodology. In the absence of this gene, skin loses its colour and pigmentation. The experiment was the first case in which genome editing of marsupials using CRISPR/Cas9 successfully achieved albinism since some of the offspring were inherited as albinos.
Generating genetically modified fertilized eggs requires the transplant of embryos into surrogate mothers. In an indistinguishable method used with rats as well as mice, the researchers transferred the fertilized egg to the womb of a fertile opossum. Pups were successfully conceived. It is the first instance of embryo transfer in marsupials.
Conclusion:
In a marsupial, the successful knockout of a gene was demonstrated for the first time. By microinjecting CRISPR/Cas9 into zygote microsomes, we have generated mutant opossums efficiently. Mutant alleles were transmitted successfully to the F1 generation. Since the biology of marsupials has now been established, researchers can now concentrate on answering all their questions. Marsupials have several unique characteristics that do not exist in other mammals, making them one of three extant mammalian subclasses.
Also read: Analysis of clinical characteristics of Takayasu’s arteritis patients
Reference:
- Kiyonari, H., Kaneko, M., Abe, T., Shiraishi, A., Yoshimi, R., Inoue, K., & Furuta, Y. (2021). Targeted gene disruption in a marsupial, Monodelphis domestica, by CRISPR/Cas9 genome editing. Current Biology. https://doi.org/10.1016/j.cub.2021.06.056
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Well written 💯