Unraveling the Reproductive Strategy of Living Organisms

At the Matsumoto Lab of the Department of Biosciences and Informatics at Keio University, fundamental research relating to reproduction and the process of ontogeny of living organisms is being conducted.

The lab is focused particularly on a primitive animal called a planarian, which has a particularly high regenerative capability and diverse reproduction modes. Researchers there are trying to shed light on the basic mechanisms of living organisms by learning from planaria.

"A planarian has an extremely high regenerative capability. Generally, no matter how many times you cut a planarian, they regenerate. Like us, planaria have brains, and like us, they also have have triploblasty. For example, the planaria is about 1 centimeter in size, but there have been stories that they can live and regenerate even if they are cut into a hundred pieces. In biology, this regenerative capabilities of planarian pertaining to regenerative medicine. However, we are interested in the reproduction mode, In general animals, their male and female genders are designed to mate together in order for fertilization to occur, resulting in the creation of the next generation. This type of reproduction method that requires the different sexes is called sexual reproduction, and this sexual reproduction, or in other words, the type of sexual reproduction that humans engage in can also be performed by planaria. Furthermore, we know that depending on the environment, planaria can switch their reproduction modes between asexual reproduction and sexual reproduction. I want to know what type of system allows them to do this, so I'm working with my students to continue research in this area."

Even in the one species, there are three type of reproduction mode as the type of breeding only through asexual reproduction, type of breeding only through sexual reproduction, and type of switching between asexual and sexual reproduction depending on the environment all exist in the natural world. In the lab, an experimental reproduction mode transformation system was developed to transform asexual planaria into sexual planaria that can reproduce sexually. By providing sexual species of planaria as bait to asexual species, ovaries and testes, etc. are formed in the bodies of planaria that had absolutely no reproductive organs. Using this experimental transformation system, the Matsumoto Lab is able to advance with research on both a molecular level and a cellular level.

"We're examining how planaria are able to switch from asexual to sexual reproduction. We call it a conversion to sexual reproduction or a change from asexual to sexual reproduction, but what we want to do is find the genes necessary for this to occur. By understanding how this switch from asexual to sexual reproduction occurs, I believe that we will be able to understand the mechanisms for switching reproduction modes."

As a recent research result, the group of researchers at the Matsumoto Lab demonstrated for the first time in the world that triploid planaria with reproductive organs implement sexual reproduction that mixes the father- and mother-derived genomes to create the next generation.

"Living creatures that engage in typical sexual reproduction have two sets of genomes, one from the father and one from the mother. Ususally, triploid organisms can not reproduce their offspring by sexual reproduction, but we demonstrated that when living creatures have three sets of genomes, which is often the case with planaria, the planaria can engage in sexual reproduction. During sexual reproduction, in the cell division system that is used to create special reproductive cells through a process called meiosis, we have learned that there are division methods that differ from others. Regarding this as well, I want to examine what can reliably create reproductive cells even in a triploid condition."





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