Marine organisms as experimental material
After training in Tokyo, Dan studied with L. V. Heilbrunn at Pennsylvania and began working at the Marine Biological Laboratory in Woods Hole in 1931. He and Jean Clark Dan later continued research at Japan’s Misaki Marine Biological Station, investigating fertilization and development in sea urchins and other invertebrates.
Observing and isolating the mitotic apparatus
Dan encouraged Inoué to improve polarized-light microscopy for observing spindles in living cells. In a separate approach, Dan and Daniel Mazia reported isolation of the mitotic apparatus from dividing sea urchin eggs in 1952. Selectively dissolving surrounding cytoplasm preserved structures for subsequent biochemical investigation.
The cell surface during cleavage
Dan also investigated cell-surface behavior during cleavage and published related work with Jean. Following living cells through successive changes connected fertilization, the cell surface and the division process within an experimentally accessible system.
References: [1]
Research stations and university teaching
At the end of the Second World War he posted a notice explaining Misaki’s scientific purpose in an effort to protect the station. He later taught zoology and served as president at Tokyo Metropolitan University, continuing research and student training while retaining connections with Woods Hole.