How did you get into the development of transgenic mouse-producing technologies?It all started with my encounter with mouse genetic engineering when I was in the United States from 1998 to 2003. Before that I was at the NIG, in Dr. Naruya Saitou’s Laboratory (Division of Evolutionary Genetics) to be precise, for my joint research in the doctoral program and later as a postdoc. I was studying molecular evolution, spending my days decoding DNA sequences and analyzing them on the computer. Then I got the opportunity to study as a postdoc in Frank Ruddle’s laboratory at Yale University. This laboratory succeeded for the first time in the world in producing transgenic mice. The laboratory was working on a new method involving the injection of large-size genes using BAC when I was there. During this period, I was able to carry out research using live individual organisms which I had always wanted to do. This experience gave me the idea of analyzing the function of genes closely related to evolution by using genetic engineering technologies.
What are your latest research achievements?The conventional transgenic mouse generation that involves injection into individual mice has an extremely low success rate of 2-3%. This is because the method necessitates pronuclear DNA injection, which tends to damage nuclei. So in our research project, we applied to mice the transposon-derived transposition enzyme (Tol2 transposase), which had already been used in zebrafish and produced positive results. In our research, we obtained two epoch-making outcomes (transposons can transpose themselves within the genome of an animal or plant cell). First, with relatively small but normal-size (below 10kb) plasmids, we performed cytoplasmic injection, instead of pronuclear injection as in the conventional method, and dramatically increased the injection rate to over 20%. The other positive result was that we proved that Tol2 transposase can efficiently transpose even huge BAC in mouse cells.
What worked well, specifically, to get such results?First, I can cite the use of Tol2 in fertilized mouse eggs. Previously, Tol2 had been used in cultured mammalian cells, but never in fertilized mouse eggs to generate individuals. Second, it was vital that we broke free from the old belief in pronuclear injection of plasmid DNA and tried cytoplasmic injection. This turned out to be a major shift in our way of thinking. Scientists used to believe that with fertilized mouse eggs cytoplasmic injection did not allow DNA incorporation into the genome.
Where did you find the key to your ideas?It was found nowhere but in the fact that I, someone who had done mouse genetic engineering, was able to work with Dr. Kawakami, who had succeeded in genetic injection into zebrafish using Tol2. At the NIG, there are various opportunities for interactions with other researchers such as in-house seminars, biological symposiums and poster sessions which often give rise to inter-lab discussions and collaborations. It was on one of such occasions that I met Dr. Kawakami and learned that he was doing joint research with researchers specializing in various model animals and was looking for someone capable of generating transgenic mice. So we agreed to work together. This happened also because I was singled out when one of Dr. Kawakami’s research partners, Dr. Kazuhiro Yagita (Osaka University), was looking for a researcher who could perform genetic injection into individual mice using Tol2.
That is to say, you made the most of working at the NIG.Exactly. I think that new discoveries and research achievements that break through conventional frameworks tend to come from small laboratories because it is possible to make small changes and work flexibly in small laboratories, which in turn makes it relatively easier to start daring research projects. Since the NIG has various laboratories, it has many opportunities for producing new ideas. The ideas I came up for our research also had the blessing of Dr. Saitou of my laboratory.
What is your future goal?I am planning to use the same method to conduct high-throughput analysis of transcription regulation genes. At the same time, I intend to continue and deepen interactions with other researchers within the NIG and do PR of the method as before.
1) A simple and highly efficient transgenesis method in mice with the Tol2 transposon system and cytoplasmic microinjection.Sumiyama, K., Kawakami, K., and Yagita, K. Genomics 95(5) 2010. DOI: 10.1016/j.ygeno.2010.02.006
2) Transposon-mediated BAC transgenesis in zebrafish and mice.Suster, M.L., Sumiyama, K., and Kawakami, K. BMC Genomics 10, 477, 2009. DOI: 10.1186/1471-2164-10-477