Hans Spemann, a pioneer in developmental biology, was born on 27 June 1869. His work helped scientists understand that cells in developing embryos influence the fate of their neighbors. As a professor at the University of Freiburg-im-Breisgau in Germany, Spemann, with graduate student Hilde Pröscholdt Mangold, conducted one of the most important experiments in developmental biology. The pair discovered a swath of cells in frog embryos that controls early cell differentiation. When they grafted a set of cells from the region that they called the "organizer" into the side of another embryo, a second body would form, joined to its host like a Siamese twin. The researchers theorized that the transplanted cells induced changes in neighboring cells, leading to today's view of development as a series of cell-cell interactions. Today researchers are sorting out more than a dozen signaling proteins produced by the organizer cells.
Hilde Mangold died in an accidental explosion at age 26, just as their paper was being published. But the discoveries, published in 1924, triggered a flurry of research in embryology, and Spemann was awarded the Nobel Prize in Physiology or Medicine in 1935. He was the first developmental biologist to win the award. He died in Freiburg in 1941.
Sources: S. F. Gilbert, Developmental Biology, 1994; The Nobel Foundation web site; and S. Shostak, Embryology, 1991