Jean Clark Dan and Katsuma Dan

A legacy of leadership in research and education

Recognizing Our Past to Strengthen our Future

Jean Clark Dan


Katsuma Dan


Jean Clark Dan
MBL Affiliation from 1931 to 1977 as Student, Faculty, Investigator and Corporation Member
Katsuma Dan
MBL Affiliation from 1931 to 1980 as Faculty, Investigator, and Corporation Member
Throughout its history, the Marine Biological Laboratory has been a place for researchers from all over the world to come together in the cause of scientific discovery. Sometimes, though, it’s been more than that. In the case of Katsuma Dan and Jean Clark, the MBL brought together two pioneering researchers from opposite sides of the globe who would not only make major contributions to developmental biology, but also forge a deep personal relationship that would be tested by separation and warfare.

The son of a prominent Japanese businessman, Katsuma Dan began his connection with MBL in 1931, while doing graduate work with L.V. Heilbrunn at the University of Pennsylvania. His main interest was developmental biology: the study of how cells divide, differentiate, and develop into organisms, using sea urchins and other marine animals as model systems, work which brought him to the MBL.

Jean Clark Dan and Katsuma Dan in their laboratory at the Misaki Marine Biological Station. Credit: Dr. Mariko Kondo, MMBS. Photo courtesy of the Woods Hole Historical Museum.

Jean Clark Dan and Katsuma Dan in their laboratory at the Misaki Marine Biological Station.
Credit: Dr. Mariko Kondo, MMBS. Photo courtesy of the Woods Hole Historical Museum.

Jean Clark, a biology student at Wilson College in Pennsylvania, held similar fascinations. Her first summer at the MBL was also in 1931, when she was a student in the Invertebrate Zoology course, and the next year she entered the University of Pennsylvania to begin graduate work with Heilbrunn. Despite Katsuma and Jean’s very different backgrounds — one the scion of a noted Japanese statesman, the other a middle-class American woman from New Jersey — their shared interests brought them together at the MBL, and they soon became both scientific colleagues and romantic partners, becoming engaged in 1934. While Katsuma returned to Japan to continue his research at the Misaki Marine Biological Station, Jean remained in the United States to finish her Ph.D. with Heilbrunn. A month after she completed her thesis in 1936, Jean and Katsuma were married in Woods Hole, then settled in Japan in 1937 after a European honeymoon.

Jean Clark Dan. Credit: MBL Archives

Jean Clark Dan. Credit: MBL Archives

They continued their research together at the Misaki Station, with Jean facing the added challenges of being a stranger in a strange land. Already at war with China, Japan was becoming an increasingly militarized and imperialistic society suspicious of foreigners. Despite the darkening clouds of political upheavals and impending global conflict, Katsuma and Jean managed to find refuge in each other and in their work.

That work was challenging enough in its own right. Much about the fundamental processes of cell division and differentiation were still cloaked in mystery, and teasing out those secrets was especially difficult with visible light microscopy. Using polarized light microscopy and working with his graduate student (and later MBL Distinguished Scientist) Shinya Inoué, Dan was the first to conclusively isolate and identify the mitotic spindle that appears during cell division, allowing it to be studied biochemically. Jean worked on microscopic studies of the fertilization process, defining the precise sequence of events that occur when sperm meets egg. Jean and Katsuma also co-authored articles on the behavior of the cell surface during cleavage.

Katsuma Dan. Credit: MBL Archives

Katsuma Dan. Credit: MBL Archives

Misaki Station was situated at the entrance to Tokyo Bay, about 40 miles from the capital city. Although not a military target, work there was increasingly affected by wartime shortages of vital supplies. Yet Katsuma and Jean were undeterred, taking the difficulties in stride.  “During the first three years of the war, our everyday life was not fundamentally affected and we could work regularly,” Katsuma recalled in a postwar letter to a friend. As the tides of war brought U.S. bombers within range of Japan, however, that changed. Still, Katsuma wrote, “Ducking under bombs was not so bad. Rather, it was a great excitement. Hide and seek at the expense of your life can’t help being exciting.”

In early 1945, the Japanese military took over the Misaki Station and transformed it into a base for midget submarines. Katsuma, Jean, and their colleagues were forced to relocate to temporary facilities nearby to continue their work as best they could. When the war finally ended and the U.S. Navy occupied the laboratory in August 1945, Katsuma rushed back to ensure the Americans wouldn’t destroy it. In a note he left behind, he explained that Misaki was a marine biological station for peaceful research and compared it to other famous facilities, including the MBL. The American military heeded Katsuma’s plea and Misaki was spared. Dan’s note, “The Last One to Go,” now hangs in the MBL-WHOI Library.

“The Last One to Go”: Katsuma Dan wrote and tacked these poster s onto the doors of the Misaki Marine Station as the demilitarization of the submarine base took place at the end of WWII.  Credit: MBL Archives

“The Last One to Go”: Katsuma Dan wrote and tacked these posters onto the doors of the Misaki Marine Station as the demilitarization of the submarine base took place at the end of WWII. Credit: MBL Archives

As Katsuma worked to get Misaki back up and running, Jean returned with their five children to their home in Nagai, where she negotiated with the occupying forces to recover land that had been taken from local farmers by the Japanese military. Her work to improve living conditions for local women and families earned her the nickname “God of Nagai.”

After a 10-year absence, Jean revisited the United States and the MBL in 1947. Through her network of friends and scientific colleagues, she acquired the first phase contrast microscope in the United States, which she brought back to Japan in 1948 as a gift for her husband. Katsuma, however, refused to accept the gift, insisting that Jean keep it and return to her scientific work. She went on to do pioneering work in invertebrate biology using electron microscopy and discovered the acrosomal reaction, a critical step in the penetration of sperm into egg during fertilization. While in the United States, Jean also arranged for a fellowship for Shinya Inoué to come from Japan and attend Princeton University.

Shinya Inoué, left, with his mentor, Katsuma Dan in 1988. Credit: MBL Archives

Shinya Inoué, left, with his mentor, Katsuma Dan in 1988. Credit: MBL Archives

Apart from their important scientific discoveries, Jean and Katsuma made significant contributions to education. Katsuma was a professor of zoology and later president of Tokyo Metropolitan University, while Jean was a professor of biology at Ochanomizu Women’s College, each training generations of new scientists. Jean also helped found the Tateyama Marine Research Center and taught there with her husband. They both maintained strong connections with the MBL and Woods Hole. After Jean died in 1978, her ashes were scattered off of Nobska Point in Woods Hole. Katsuma died in 1996; among those who paid tribute in published obituaries was Shinya Inoué.

Katsuma Dan and Jean Clark–both individually as brilliant researchers and educators and together as life partners whose bond remained strong through the most tumultuous years of the 20th century–provide a shining example not only of the global influence of the MBL, but also the capacity of science to transcend national borders and political hostility for the benefit of humanity.

–By Mark Wolverton

Selected References

Jean Clark Dan and Katsuma Dan published most of their research articles in the MBL journal, The Biological Bulletin. Full text is available online through the Biodiversity Heritage Library.

Colwin, Laura Hunter and Arthur L. Colwin (1979) Obituary: Jean Clark Dan. Nature, DOI: 10.1038/278492a0

“History of MMBS (Before WW 2), Misaki Marine Biological Station website.

Imamura, Rio, “Last One to Go,” Riosloggers blog.

Inoué, Shinya. Mechanisms of Fertilization and the Contributions of Jean Clark Dan. Presentation to the MBL Frontiers in Reproduction course, June 4, 2010. Archived with the MBL Archives.

“Obituary: Dr. Katsuma Dan, 91, of Japan; Was a Leading Marine Biologist,” New York Times, May 27, 1996.

Okada, Masukichi, Hikoichi Sakai and Shinya Inoué (1996) Obituary: Katsuma Dan. Develop. Growth Differ. 38, 449-451.

Wolverton, Mark, “A Plea to the Victors: Amid Defeat, a Hopeful Japanese scientist Bet on His Institution’s future,” World War II Magazine, March/April 2016, 62-64.

A gift in Jean and Katsuma’s honor will support The Jean and Katsuma Dan Endowed Lectureship, an annual lecture in the Embryology or Physiology courses.
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