Yoshio Masui is a biologist who studies the biochemical mechanisms of cell division. Yoshio invented several new experimental techniques, including microinjection and microextraction systems, which enabled him to investigate cell development factors directly.

The cell cycle is the process within a cell that leads to its division into two identical cells. By developing techniques that enabled him to manipulate the contents of cells, Yoshio was able to measure and compare the influence of various substances on the cell cycle. With this experimental approach, Yoshio confirmed that controlled amounts of a molecular complex called maturation promoting factor initiates cell division whilst the cytostatic factor halts it.

Unlike other nuclear transplantation and cell fusion systems, Yoshio’s techniques take cytoplasm — the gel-like substance enclosed within the cell membrane — from particular stages of the cell cycle and transplants it into new cells, causing them to transition from one phase of the cell cycle to another.