From Pennsylvania to Misaki
Dan studied biology at Wilson College and undertook graduate research with L. V. Heilbrunn at Pennsylvania, completing her doctorate in 1936. She met Katsuma Dan at Woods Hole and moved to Japan in 1937, continuing fertilization research at Misaki Marine Biological Station.
Watching living sperm with phase contrast
In 1948 she brought a phase-contrast microscope to Japan. Its ability to reveal transparent, low-contrast living cells let her follow structural changes as sperm approached eggs. A University of Tokyo historical account records her observations of the acrosome reaction in marine-animal sperm using this instrument in 1950–1952.
References: [2]
Distinguishing aggregation from the acrosome reaction
In a 1954 study, Dan compared sea urchin sperm under calcium-deficient conditions. Sperm could remain motile and aggregate after exposure to egg water without a detectable acrosome reaction. The study distinguished aggregation from the structural reaction, showing why observing clumping alone could not substitute for investigating the fertilization process.
References: [3]
Teaching and international connections
She later researched and taught at Ochanomizu University and helped Inoué obtain an opportunity to study at Princeton. She linked Woods Hole, Japanese marine stations and university laboratories while continuing collaborative research with Katsuma on cell-surface behavior during cleavage.