Chronology of Stem Cells

1963

McCulloch and Till illustrate the presence of self-renewing stem cells in mouse bone marrow. Ernest Armstrong McCulloch is a Canadian cellular biologist, best known for demonstrating – with James Till – the existence of stem cells.

McCulloch was born in Toronto and studied medicine at the University of Toronto. His experience in hematology, when combined with Till's experience in biophysics, yielded a novel and productive combination of skills and interests. Till was working in Ontario Cancer Institute which McCulloch joined in 1957. In the early, McCulloch and Till started a series of experiments that involved injecting bone marrow cells into irradiated mice. Nodules were observed in the spleens of the mice, in proportion to the number of bone marrow cells injected. Till and McCulloch called the nodules 'spleen colonies', and speculated that each nodule arose from a single marrow cell: perhaps a stem cell.

In later work, Till and McCulloch were joined by graduate student Andy Becker, and demonstrated that each nodule did indeed arise from a single cell.

1960s

Joseph Altman an independent researcher at MIT and Gopal Das present evidence of adult neurogenesis, ongoing stem cell activity in the brain; their reports contradict Cajal's "no new neurons" dogma and are largely ignored. Joseph Altman is accrediated with the discovery of adult neurogenesis, the creation of neurons at adult brain. Before this period it was believed that the brain cells mainly neurons donot have the regenerative property and thus there was a wide spread belief that neurons cannot be formed in adults which left the Altman discovery in sidelines. In the late 1990s, the fact that the brain can create new neurons even into adulthood was rediscovered. Altman Continued his research at purdue university. He is now retired.

Ramón y Cajal was born in Petilla de Aragón Navarrese enclave in Aragon. Ramón y Cajal attended the medical school of Zaragoza, from which he graduated in 1873. Ramón y Cajal's most famous studies were on the fine structure of the central nervous system.

Ramón y Cajal's most famous studies were on the fine structure of the central nervous system. Golgi found that by treating tissue with a silver chromate solution, a relatively small number of neurons in the brain were darkly stained. This allowed him to resolve in detail the structure of individual neurons and led him to conclude that nervous tissue was a continuous reticulum (or web) of interconnected much like those in the circulatory system. Using Golgi's method, Ramón y Cajal reached a very different conclusion. He postulated that the nervous system is made up of billions of separate neurons and that these cells are polarized. Rather than forming a continuous web, Cajal suggested that neurons communicate with each other via specialized junctions called "synapses", a term that was coined by Sherrington. This hypothesis became the basis of the neuron doctrine, which states that the individual unit of the nervous system is a single neuron. Electron microscopy later showed that a plasma membrane completely enclosed each neuron, supporting Cajal's theory, and weakening Golgi's reticular theory. However, with the discovery of electrical synapses (direct junctions between nerve cells), some have argued that Golgi was at least partially correct. For this work Ramón y Cajal and Golgi shared the Nobel Prize in Physiology or Medicine. Ramón y Cajal also proposed that the way grow is via a growth cone at their ends. He understood that neural cells could sense chemical signals that indicated a direction for growth, a process called
chemotaxis.