Susumu Tonegawa

Susumu Tonegawa is a Japanese molecular biologist who discovered the genetic mechanism that allows the immune system to generate an enormous diversity of antibodies capable of recognizing a vast range of foreign invaders from a comparatively limited amount of genetic material. Working in Switzerland in the late 1970s, Tonegawa showed that the genes coding for antibodies are not fixed in an animal's DNA from birth but are instead assembled through a process of programmed genetic rearrangement, in which separate gene segments are cut and recombined in different combinations within individual immune cells, a process now called V(D)J recombination, allowing a relatively small number of gene segments to be combined in an enormous number of ways to produce antibody diversity. This discovery resolved a long-standing puzzle in immunology and earned Tonegawa the Nobel Prize in Physiology or Medicine in 1987, awarded solely to him for the discovery of the genetic principle for generation of antibody diversity. Later in his career Tonegawa shifted his research focus to neuroscience, leading a laboratory at the Massachusetts Institute of Technology studying the molecular and cellular basis of learning and memory formation in the brain, including influential work using genetically engineered mice to study how specific populations of neurons encode individual memories.