Innovation Story
Researcher Interview #2
Professor, Graduate School of Integrated Life Sciences, Hiroshima University
He was an assistant professor at the Faculty of Biological Science, Hiroshima University, an assistant professor at the Graduate School of Biosphere Science, Hiroshima University, and an associate professor at Hiroshima University before assuming his current position. He is conducting a variety of research projects that combine basic research on chicken stem cells with genome editing technology.
Mr. Hiroyuki Horiuchi
The key to developing hypoallergenic eggs is genome editing and a change in thinking
The protein ovomucoid, which is an allergen in egg allergies, is removed from eggs.
Professor Hiroyuki Horiuchi of Hiroshima University has used genome editing technology to lay the foundation for research and development of hypoallergenic eggs.
It has taken about 15 years of research to get to this point, and the road has been full of twists and turns.
After overcoming each difficult hurdle one by one, they finally created chickens that lay eggs that do not contain ovomucoid.
The passion that underpinned his tireless research, the latest technology that led to the realization of hypoallergenic eggs,
We asked him about what goes on behind the scenes of his research, focusing on how he changes the way he thinks.
One high wall after another
--What prompted you to start researching hypoallergenic eggs?
Horiuchi : As I continued my research on chickens, I became aware of the problem of the large number of people who suffer from egg allergies. The academic field in which I specialize is expected to be immediately useful to society, and I thought that if I could reduce or eliminate the allergens in eggs, I could help patients.
--Did the research go smoothly?
HORIUCHIWe ran into a variety of problems and hit a wall each time. Things that can be done relatively easily with mice are not possible with chickens.
For example, with mice, it is possible to create many fertilized eggs in a dish, and then it seems that genome editing can be performed on those fertilized eggs. However, with chickens, it is not possible to create fertilized eggs in a dish. After fertilization, the chickens must be dissected one by one and the fertilized eggs must be extracted from their bodies. This is extremely inefficient and also raises the issue of animal welfare.
So instead of genetically modifying fertilized eggs, Mr.Horiuchi
ES cells (embryonic stem cells, capable of producing all the cells in an animal's body)
So they started researching genetic modification.
--How did genetic modification of ES cells progress?
Horiuchi: Initially, we were conducting research using gene recombination techniques. However, with this method, foreign genes enter not only the targeted location, but also other locations. This inevitably leads to abnormalities in the cells. When gene recombination was performed using our method, about 90% of the cells became abnormal. Unless this problem was solved, genetic modification of ES cells would not be possible. After much consideration, we arrived at genome editing. Around that time, we happened to meet again with Dr. Taku Yamamoto (Professor at Hiroshima University).
I met Yamamoto, who is researching genome editing, when he was a doctoral student at the Faculty of Science at Hiroshima University. After that, even after we both changed jobs, we continued to come into contact through our research, and we met again at Hiroshima University.
--Did your reunion with Yamamoto affect the progress of your research?
Horiuchi : It had a big impact. Genome editing does not involve recombining genes, but rather involves proteins acting to cut genes and causing mutations through the inherent functions of cells. With the help of Dr. Yamamoto, we introduced genome editing, and the abnormal cells that were generated when genes were recombined were greatly reduced.
--So things went smoothly.
Horiuchi : However, another problem arose. Although they were able to confirm that the genome-edited ES cells were able to develop into eggs and sperm, the eggs and sperm did not fertilize.
--If the eggs are not fertilized, chickens that lay hypoallergenic eggs will not be born.
HoriuchiIf the genes of chickens that lay allergy-reducing eggs are not passed down from generation to generation, they cannot contribute to society. Therefore, we gave up on genetic modification of ES cells and switched to genetic modification of primordial germ cells. Primordial germ cells are reproductive cells, as the name suggests, so they will be passed down to the next generation.
Primordial germ cells (PGCs) are the cells that give rise to sperm and eggs. Inside an egg are egg white, egg yolk, and embryo, and during the development process, blood vessels extend from the embryo that will become the chicken's body to the egg yolk, which provides nutrition. PGCs circulate in this bloodstream for a certain period of time. Horiuchi conducted research into genome editing of PGCs extracted from the bloodstream.
-Was the research into genetically modifying PGCs progressing smoothly?
Horiuchi: This also presented challenges. For gene modification to be successful, it is better to have more PGCs. So we tried to grow the collected PGCs by culturing them, but they didn't grow at all. We read a paper on previous research and cultured them exactly as instructed, but they didn't grow at all. After much trial and error, we came to the conclusion that we had no choice but to find an original method.
What is the original method?
Horiuchi: Rather than trying to increase their numbers , we tried to prevent them from decreasing. When the harvested PGCs were transferred to a dish, they began to die one after another. Since the cells were being transferred to an abnormal environment, we thought that apoptosis (programmed cell death) might be occurring. We came up with the idea of applying a small molecule inhibitor that blocks apoptosis to PGC culture, and when we tested it, it worked. After we cleared up the culture issue, things went smoothly.
This was made possible thanks to genome editing technology
--It seems like your research has been a long journey that has involved overcoming many hurdles. By the way, would you say that the development of hypoallergenic eggs was only made possible by genome editing technology?
HORIUCHI : I think you can say that. Genetic engineering was working well up until a certain point, but if we had continued with it, research would have been delayed considerably.
--The genome editing of the hypoallergenic eggs uses the "Platinum TALEN" genome editing tool patented by Hiroshima University, which acts as the "scissors" to cut the genes. Why did you choose Platinum TALEN?
Horiuchi 's research into allergy-reducing eggs has had social implementation in mind from the beginning. In that respect, other leading genome editing tools, CRISPR-Cas9, have complicated patent relationships and high patent fees, which could be an obstacle to social implementation. In contrast, Hiroshima University holds the patent for Platinum TALEN, and there are almost no "off-target" problems with genome editing (cutting and modifying genes that are not the target). After consulting with Yamamoto, we decided to proceed with the research using Platinum TALEN. In fact, the research has revealed that there are no problematic off-targets.
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Genome editing is safer than natural mutations
--However, there must be quite a few consumers who are concerned about the safety of genome editing. Compared to selective breeding through natural mutations, how safe is genome editing?
Horiuchi : Actually, mutations are introduced through selective breeding. Moreover, they are introduced in various places, and it is not clear where they are. In contrast, with genome editing, it is clear where the mutations are introduced. The results can also be properly evaluated. If you ask which is safer, we can confidently say that genome editing is safer. In that sense, our attempt to reduce allergens places importance on the consumer's perspective.
INTERVIEWER What do you think about the importance of genome editing in the future of society?
Horiuchi : I believe that genome editing is essential to respond to this drastic change in the global environment. Without genome editing technology, we would not be able to overcome global warming, energy problems, food problems, and other issues.
--If it's such an important technology, it's important to make sure that general consumers understand its safety.
Horiuchi : I think many people have some misgivings about genome editing. Although I feel uncomfortable with genome editing for the sake of benefits such as resistance to herbicides and pests, which are highly profitable for producers, there are many things that are easy to understand, such as high nutritional content and reduced allergens, as in this case. For that reason, it is important to first let people know about genome editing itself and examples. I also intend to provide more information than ever before.
