Topics that shape the future
- Closer look at research results -

Inside cells, various organelles such as mitochondria and proteins are actively moving. Chromosomes, which carry genetic information, are made up of condensed string-like molecules called chromatin, which is a complex of DNA and proteins, and it has been found that this chromatin also moves in a similar way. Recent research has shown that when looking at cells in the early stages of development, the movement of chromatin also decreases as embryonic cell division progresses from the 2-cell stage to the 4-cell stage to the 8-cell stage.
As the cell divides, the size of the cell nucleus that contains the chromosomes decreases. Therefore, it has been speculated that the movement of the chromosomes becomes slower as they are confined in a small space, like the inside of a crowded train. It is also easy to imagine this if you think of the thickening polysaccharides used in foods, but as the concentration of chromatin, a long, string-like polymer, increases, it becomes more viscous, and the movement becomes slower.
The theme of this research is to elucidate the movement of chromatin within cells and its laws, which have until now only been speculated upon.

So why does motility decrease with development? Earlier, we talked about viscosity, and it is true that the viscosity increases inside the cell nucleus, which contains a high concentration of chromatin, a polymer. However, this is a macroscopic (nuclear) issue. Looking at the details, the inside of the cell nucleus is like a mesh made of chromatin, and the inside of this mesh is relatively smooth. Therefore, when considering the movement of chromatin, we need to distinguish between movement on a scale smaller than the mesh that occurs in a short period of time, and movement on a scale larger than the mesh that occurs over a long period of time. The size of the mesh becomes smaller as the size of the cell nucleus decreases with the progression of embryonic development. A decrease in the size of the cell nucleus means an increase in the concentration of chromatin, so taking this into account, it is intuitive to understand why the mesh size becomes smaller.
To summarize the argument, as embryo development progresses, the size of the cell nucleus decreases, and the mesh size that characterizes the spatial structure of chromatin within the cell nucleus also becomes smaller. Furthermore, the chromatin movement properties change qualitatively at the mesh size boundary. At this point, it naturally follows that in order to appropriately compare chromatin movement in cells at different developmental stages, the idea of re-measuring the distance traveled by the movement using the mesh size as a "ruler" is reached.

Which scientific journal to publish a paper in is one of the points that researchers must consider, but this time I chose "Physical Review Letters" which has a high impact factor because I wanted more scientists, especially biology researchers, to know that we have been able to reduce the movement of chromatin in a complex living organism to such a simplified mathematical formula. I had several exchanges with the reviewers asking "Can it really be explained so simply?" and had them confirm it over and over again. As a result, it was deemed persuasive enough and was published.
Our research team would like to promote this result to as many people as possible, so we continue to introduce it at academic conferences and other occasions when we have the chance, and people have shown a great deal of interest in it.

Physicists are always trying to find universals in phenomena. It was a truly valuable experience for me to take on the big challenge of finding universality in the extremely complex existence of living organisms. Furthermore, in a broader sense, this research is related to Brownian motion theory, which has always interested me. I would like to continue researching Brownian motion, and also explore the phenomenon of life from the perspective of statistical physics and soft matter physics.