Researchers successfully create genetically engineered marsupials via genome editing

Scientists from the RIKEN Center for Biosystems Dynamics Research (BDR) successfully created the first genetically engineered marsupial. The research and its findings published in the Current Biology journal help decipher the genetic background of special characteristics found only in marsupials.

Researchers successfully create genetically engineered marsupials via genome editing
Genome editing targeting a gene responsible for making body pigments resulted in albino offspring, suggesting that the genetic engineering was successful in marsupials. Image Credit: RIKEN Center for Biosystems Dynamics Research

Genetically modified animals, rats and mice, in particular, are extremely vital tools for researching biological processes. For instance, scientists often silence genes to identify their normal functions. As marsupials possess unique characteristics, studying them demands the development of a representative animal model.

Until now, the best choice is the opossum, which is considered to be the ancestor of all marsupials. The opossum is the first marsupial whose entire genome is sequenced. Furthermore, its breeding characteristics and size are similar to those of rats and mice, making it a good model animal.

Similar to other marsupials, the opossum has unique characteristics that are not found in other mammals. It forms without a functional placenta, and pups are born prematurely. Similar to humans, and not any other non-marsupial mammals, it gets skin cancer by ultraviolet light exposure.

Furthermore, in contrast to other mammals, newborn opossum pups with spinal cord injuries can heal themselves naturally. Owing to these unique characteristics, studying marsupial biology is gaining wider attention. Yet, the analysis of their underlying genetics is not possible without established technology to genetically modify marsupials.

The scientists headed by Hiroshi Kiyonari at RIKEN BDR have been leveraging new gene-editing technology to initiate opossum research.

Genome editing involves the systematic collection of fertilized eggs, as the solution for genome editing is injected into the fertilized eggs. As opossums have a lengthy estrus cycle and a strong sense of territoriality, it takes about a week for a couple to mate even if they live together, making it difficult to proceed with the experiment systematically.

The scientists administered a hormone used in mice and other laboratory animals to stimulate estrus in the females and succeeded in substantially shortening the mating time.

To generate a genome-edited fertilized egg, it is necessary to transplant the embryo into a surrogate mother. Similar to what was done in rats and mice, the scientists transferred the fertilized egg into the uterus of a fertile female opossum and successfully obtained pups. This is the first occasion that embryo transfer technology is established in marsupials.

Generally, the solution required for genome editing is injected into the fertilized egg with the help of a fine needle. As the fertilized egg of the opossum is covered by a thick layer of proteins and a hard shell-like structure, the injection needle cannot penetrate it.

One of the tricks to our success was using a piezoelectronic element along with the needle, which allowed the needle to penetrate the hard shell coat and thick layer surrounding the egg. The piezo has thus made it possible to inject zygotes without significant damage.”

Hiroshi Kiyonari, Laboratory for Animal Resources and Genetic Engineering, RIKEN Center for Biosystems Dynamics Research

To ascertain the overall process, scientists targeted a gene responsible for making body pigments. While the gene is disrupted, pigment production halts, resulting in a lack of skin color. Some of the offspring produced as a result of this experiment were albino, and their genes were inherited by the next generation. This portrays the first successful gene editing in marsupials.

As the methodology is now established, scientists can focus on answering all their questions about marsupial biology.

Marsupials represent one of three extant mammalian subclasses with a number of unique characteristics not shared by other mammals. Having established the technology in this proof-of-concept experiment, future studies can create genetically modified marsupials that will impact the fields of mammalian embryology, genomic imprinting, reproduction, neurobiology, immunogenetics, cancer biology, and even comparative evolution.”

Hiroshi Kiyonari, Laboratory for Animal Resources and Genetic Engineering, RIKEN Center for Biosystems Dynamics Research

Source:
Journal reference:

Kiyonari, H., et al. (2021) Targeted Gene Disruption in a Marsupial, Monodelphis domestica, by CRISPR/Cas9 Genome Editing. Current Biology. doi.org/10.1016/j.cub.2021.06.056.

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