![リガクル[RIGAKU-RU] Exploring Science](/ja/rigakuru/images/top/title_RIGAKURU.png)
Beauty under the microscope
It happened when Professor Ohsugi was a graduate student in the Department of Biophysics and Biochemistry*.
“One time, I attended the annual meeting of the Japan Society for Cell Biology with one of my seniors. I saw a poster presentation with a mesmerizing picture of a cell and immediately thought, “I probably like this more” (laughs). At the time, I was doing molecular biology research, and my experimental results of biochemical analysis and detection were represented with black-and-white bands. It was a monochrome world.”
After completing her doctoral studies, Ohsugi began researching cell division at The University of Tokyo's Institute of Medical Science as a postdoctoral fellow. She had indeed changed her research field to the one she “liked more,” from molecular biology to cell biology.
“When a cell divides, the chromosomes (“clusters” of DNA) split in two. In about an hour, the chromosomes almost “come alive,” moving dynamically. I loved watching this unfold under the microscope. I wanted to know how such beautiful movements could arise. Wanting to discover the underlying mechanisms has driven my research ever since.”
Fascinated by the beauty and mystery of the microscopic world of life under the lens of a microscope, Ohsugi gradually became more and more interested in the wonders of mammalian fertilization and development, the point where life begins.
“I was studying cell division using HeLa cells, a well-known cultured cell line (isolated from human cervical cancer tissue, cultured and preserved). Eventually, I began to wonder if studying something that had been cultured for such a long time could still be hiding unseen phenomena. At that time, I was analyzing knockout mice (mutant mice deficient in a specific gene) created for research on a certain molecule. In these mice, abnormalities appeared in the embryos immediately after fertilization. I wanted to find out why, so I shifted the focus of my research to my current theme of fertilization and preimplantation development using mice.”
Fertilization produces a zygote, which repeatedly divides to form an embryo, the beginnings of a specimen. This process has been investigated using vertebrates whose eggs are easy to study, such as frogs and fish. Mammalian embryonic development, however, has not been well understood because the process occurs inside the female's body and cannot be observed directly. What happened in the knockout mouse only added to the list of “unknowns.”
“In the past half-century, it has become possible to quite proficiently culture mammalian zygotes in vitro. As a result, it has become clear that mammals differ from other vertebrates in many respects. However, we still do not know much about the reasons and molecular mechanisms causing these differences. There must be something unique in the structure of fertilization and development in mammals compared to other vertebrates. I want to know that mechanism. I want to understand it. That is where my curiosity is currently pointing to; that is the question I am seeking an answer to. That is why, as a rule for myself, I have decided not to do research that would lead to the same discoveries when done on frogs or fish.”
The excitement of “reasoning”
Ohsugi was drawn in by the world seen under a microscope, but cell biology has another, similarly striking characteristic technique using the microscope called “live-cell imaging.”
“In cell biology, cell walls are not ground. In other words, we look at their details as they move and multiply with their morphology intact. This is what live-cell imaging is all about. However, it is also interesting to investigate how the differences in cell biology can be explained in terms of molecular biology,” says Ohsugi.
“The question is how far “down” we go in our approach. Is it the level of cells visible under a microscope? Or is it down to the level of organelles such as mitochondria and chloroplasts within the cell? Or is it down to the molecules that make up the organelles? I am the type of person who goes down to the level of molecules, and I suspect many researchers have a similar approach. I think there are very few cell biology studies that do not incorporate molecular biology at all.”
So, what is the actual process of conducting research?
“For example, if we want to understand the function of a certain molecule, we could use an inhibitor (a substance that interferes with the activity of an enzyme) to suppress its function and observe what happens. We want to observe changes in the appearance of the chromosomes and what molecules, where, and how many are present. To do this, we artificially create messenger RNA and microinject it into the eggs. Microinjection is a technique in which we use a microscopic glass tube and inject the RNA under a microscope. By doing so, we can visualize various organelles such as chromosomes and microtubules and make them visible under a fluorescence microscope. We then set them under the microscope and fertilize the eggs or provide a stimulus similar to fertilization and watch them develop, noting changes at intervals of a minute or five minutes.”
All of this is also recorded as image data, which is analyzed after the experiment is over. It is a time-consuming process that requires perseverance.
“In experiments that require detailed observation, we can observe only one egg at a time. In such cases, because it takes about three hours for a zygote to form, we can only experiment with two eggs by repeating it twice a day. For a single theme, we observe about 20 to 30 eggs. And since we are also observing the comparison subject, it can take several months.”
She also says that “reasoning” is crucial to research.
“I enjoy reasoning and formulating hypotheses. I find these elements of research exciting.”
Similar genes in mice may work differently from their function in frogs and fish. Therefore, there might be phenomena unique to mammals. Scientists formulate such hypotheses and construct experiments accordingly. In other words, they use reasoning based on the accumulated knowledge of past research.
“To verify the hypothesis, we design experiments and try to make predictions about the results. I find such conceptualization and implementation the most enjoyable parts of research.”
“Life” is still full of mysteries
Let us return to the fact that the processes of fertilization and development are different in mammals from other vertebrates. The following is one such unique phenomenon.
From the fusion of the egg and sperm to the formation of a zygote takes most animals about 30 minutes. In mammals, however, it takes two to three hours.
“If you introduce a phosphatase, an enzyme that removes a phosphate group from proteins, into a mouse zygote, you can shorten the process, which normally takes about 110 minutes, to about 40 minutes. When we look at what happens at this point, we find that the chromosomes that come from the sperm are not functioning properly. A zygote is produced, but when it first divides (first cleavage), the sperm-derived chromosomes do not line up properly, or the chromosomes remains in the middle, without splitting.”
Repeating this experiment revealed that the number of anomalous zygotes increases when the zygote takes less than 80 minutes to form. Why does this happen in mice, i.e., in mammals, but not in frogs and fish? Why do mammals need more time?
“Our research showed that a particular kinase (an enzyme that adds a phosphate group to proteins), which in other animals stops the egg from dividing until the sperm arrives, somehow slowed down the formation of the cell nucleus in mammals. In other words, because the role of some of these molecules was different in different animals, a series of changes occurred and accumulated, leading to different phenomena.”
Turns out, over time, the sperm-derived nucleus can only start functioning after the formation of the zygote, for which the egg-derived chromosome provides the mechanisms.
“We now have a rather good understanding of the phenomena that occur and how time is controlled. On the other hand, there are still many details that are not yet clear, such as which processes are cut short in the sperm when the timeframe is shortened.”
The high school biology curriculum includes fertilization and the repeated cell division afterward. So, the assumption could be that the details of this stage of development have long been discovered. But not so, says Ohsugi.
“There are still many things we do not understand. For example, in cell mitosis (when the nucleus divides in a cell, the chromosomes split in two to form two daughter cells), we know what happens in what order at the cellular level, but we are only now beginning to understand what is driving what and how at the molecular/organelle level.”
One such “mystery” that Ohsugi is currently working on concerns the number of sets in the genome.
“Mammals are diploid, meaning they have two sets of genomes. Mammals are extremely sensitive to changes in the number of sets. Artificially produced fish with triploid (three sets) genomes just become large, meaning they provide more meat we can eat, which is good for the industry. However, mammals with triploid and tetraploid genomes cannot even be born. One wonders why these animals are so sensitive to changes in the number of sets of chromosomes. I have a hypothesis for this, which I am now beginning to test.”
Reasoning and formulating hypotheses are what Ohsugi finds the most exciting about research.
Small rather than grand mysteries
“To me, getting unexpected results after coming up with a hypothesis and conducting an experiment is the most enjoyable part of the research process.”
It is not the kind of enjoyment one might experience when the hypothesis is proven correct. It is quite the opposite.
“I think the hypotheses that people like me can come up with are rather limited because they are within the scope of what can be expected from our accumulated knowledge. Instead, I find it much more interesting when the results point to an answer that is completely unexpected, even when the experiment is executed with utmost care. It would suggest that we have discovered an entirely new concept in our understanding of “life” and that something unexpected was happening. What is it? I have the most fun when I am forced to look at things from a different point of view or when I see a new, unknown phenomenon.”
On such days, Ohsugi spends the entire night searching for and reading relevant papers.
“In the natural sciences, there are always clues in past research. How much do we already know about the phenomenon I am beginning to grasp? What can I do to verify my hypothesis? I start researching all kinds of things to formulate new hypotheses and experiments to test my ideas. I have so much fun doing this that it feels like the time of the last train arrives in the blink of an eye. Even if there is a meeting I have to attend, I do not want to leave my office (laughs). I can get completely absorbed.”
Ohsugi says that she is suited to be a researcher. She says that research is so much fun she cannot stop herself.
“Just when you think you have figured one thing out, two or three more mysteries pop up, one after another. The mystery never ends. My research style is truly “curiosity-driven.” Even though I aim to understand the mechanisms unique to mammals, I tend to go from one question to another. Phenomena that I want to understand keep popping up, and I am here for it.”
Ohsugi says that thinking about “how she, herself, could have been born” naturally draws in the great mystery surrounding mammalian births.
“Studying mammals makes me realize how much of a miracle the birth of a baby is. So, it makes me wonder about the kinds of miracles that I, as a human being, must have undergone as well. The zygote of a mouse and that of a human are not too different in size. The human one is just a little bit larger. When I look at the zygote of a mouse and think that this is how I started as a human being, I am amazed that I have grown so much. I am truly amazed by the mechanisms that make the zygote of a mammal, including myself, grow to the size of a creature that can move inside a female's body. I wonder about the miraculous process through which a baby is born. That is the question I am seeking an answer to.”
When asked for a message to young scientists, Ohsugi responds as follows.
“Research can be tough, but the fun usually outweighs the hardships, so please take the plunge. I also want to tell particularly to women that many women in science are doing whatever it takes to not pass on the hardships that we have experienced to the next generation, and things are changing rapidly. It would be nice to have more women in science to collaborate with. I also want young girls to get a chance to experience how fun research can be. So much so that I do not know how to express this feeling in words.”
Ohsugi smiles, looking troubled, but her message has undoubtedly come through.
(*2014) (Merged with the Department of Biological Sciences)
※Year of interview:2025
Interview/Text: OTA Minoru
Photography: KAIZUKA Junichi
Related articles
