Charles Philippe Leblond (February 5, 1910 – April 10, 2007) was a pioneer of cell biology and stem cell research and a Canadian former professor of anatomy. Leblond is notable for developing autoradiography and his work showing how cells continuously renew themselves, regardless of age.
Main research interests In 1946, Leblond found that, when he poured liquid photographic emulsion on a histological section containing a radio element, the emulsion was eventually activated by the radio-element; and if thereafter routine photographic development and fixation were applied to the emulsion-covered section, black silver grains appeared in the emulsion wherever it overlay sites containing a radio-element. This liquid emulsion approach has been used to develop a new high-resolution autoradiography procedureBélanger, L.F. and C.P. Leblond. A method for locating radioactive elements in tissues by covering histological sections with a photographic emulsion. Endocrinology. 1946, 39, 386-400. characterized by close contact between emulsion and section. Such close contact makes it possible to localize the radio-elements in the section at high resolution, so that radio-elements can be localized at high magnification in the light microscope.Gross, J., R. Bogoroch, N.J. Nadler and C.P. Leblond. The theory and methods of the radioautographic localization of radio elements in tissues. Amer. J. Roentgenoi. 1951, 65, 420-468.Kopriwa, B. and C.P. Leblond. Improvements in the coating technique of radioautography. J. Histochem. Cytochem. 1962, 10, 269-284.
This procedure has been utilized to examine some of the dynamic features of body components, with the main findings as follows:
The existence of stem cells in adult organs, as shown by autoradiography with labeled thymidine. The continuity of protein synthesis in living cells, as shown by autoradiography with labeled amino acids. The key role of the Golgi apparatus in protein glycosylation, as shown by autoradiography with labeled hexoses.
His results threw doubt on the validity of three traditional concepts dear to biologists in the earlier part of the twentieth century: "stability" of the cell, in which the cell and its components are unchanging, permanent structures; "specificity" of cell function, in which each cell type has a distinct, unique function; and "activity-rest alternation" of cell function, in which each period of cellular activity is followed by a period during which the activity ceases.
He has proposed replacing cell "specificity" by "multipotentiality", "activity-rest alternation" by "continuity" and "stability" of cell components by "renewal". These various results have provided the foundation not only for modern stem cell research, but also for modern cell biology.
As Nobel laureate George Palade noted on the occasion of the 1992 Prix Marie-Victorin to Leblond, Charles Leblond's discoveries are so fundamental that they are taught in schools and colleges throughout the world.
Biography
Early days
CP Leblond was born in Lille, France, in 1910, the son of a building contractor who died when Leblond was only 10 years old, leaving his mother to raise four boys on her own. A brilliant student, Leblond debated becoming a film producer, an architect or a scientist. In the end, he decided on science, and enrolled in Medicine at the University of Paris. He was fascinated by his first course in histology and decided to pursue this field as a career.
Leblond obtained his M.D. degree from the University of Paris in 1934. His doctoral thesis described the histochemical localizion of ascorbic acid, which he found to predominate in steroid-secreting cells.A. Giroud et C.P. Leblond. Etude histochimique de la vitamine C dans la glande surrénale. Arch. Anat. microse. 1934, 30, 105 129. This study led him, with a Rockefeller postdoctoral fellowship in hand, to the endocrinology-orientated Department of Anatomy at Yale University in 1935, where he carried out studies on factors influencing maternal behavior..C.P. Leblond. Extra hormonal factors in maternal behavior. Proc. Soc. Exp. Biol. Med. 1938, 38, 66 70. It was here that he met his wife Gertrude Sternschuss, to whom he was married for 64 years. Leblond had 4 children for which he chose names starting with the letter "P": Philippe, Paul, Pierre and (Marie)-Pascale. He also had 7 grandchildren.
In 1937, Leblond joined the Laboratoire de Synthese Atomique in Paris which was involved in preparing radioactive isotopes for use in investigating the fate of various molecules in biological processes. Under the guidance of Antoine Lacassagne, Leblond injected radioiodine-128, into a rat and found that the label promptly accumulated in the thyroid gland, presumably incorporated into the thyroid hormone precursor thyroglobulin.C.P. Leblond et P. Sue. Passage de l'iode radioactif (1128) dans la thyroide stimulée par l'hormone thyréotrope de l'hypophyse. C.R. Soc. Biol. 1940, 133, 543. To localize this label more precisely within the thyroid tissue, Leblond attempted to use the novel technique of autoradiography.
Unfortunately, Leblond's first attempt to use autoradiography failed, the reason being that the radioiodine-128 isotope, with its extremely short half-life (25 minutes), disintegrated so quickly that too little radioactivity remained to be detected by the photographic emulsion.
Development of autoradiography In 1941, Leblond moved to McGill University as a lecturer in histology, and quickly rose to assistant (1943), associate (1946), and then full professor of anatomy (1948). He served as the chair of the Department of Anatomy from 1957 to 1974.
At McGill, Leblond used the newly-available radioiodine-131 with a half-life of 8 days, to repeat his autoradiographic experiment on thyroid tissue. With this method, the resolving power was less than 100 μm, but nonetheless he was able to localize the radioactivity to specific thyroid [follicles].C.P. Leblond. Extra hormonal factors in maternal behavior. Proc. Soc. Exp. Biol. Med. 1938, 38, 66 70.
Leblond's early career at McGill was interrupted by World War II, during which he served in the Free French Forces. He was dispatched first to Rio de Janeiro, then to London, where he conducted medical exams of would-be soldiers.
"In 1946, after returning to Montreal from service with the Free French Forces, it was clear to me that the crude technique previously used for radioautography had to be improved".Leblond CP. The time dimension in cell biology. FASEB J. 1995 Sep;9(12): 1234-8. In collaboration with Leonard Bélanger, Leblond worked on increasing the resolution of the autoradiographic technique. They were advised by physicist Pierre Demers to melt the emulsion from Eastman Kodak lantern slides, paint it directly on the sections, and then develop the emulsion while it was still attached to the histologic sections. This resulted in a tenfold improvement in resolution.F. Bélanger and C.P. Leblond. A method for locating radioactive elements in tissues by covering histological sections with a photographic emulsion. Endocrinology 1946, 39, 386 400. Subsequently, Leblond and his colleagues developed a technique in which the histologic slides were dipped directly into liquid emulsion.C.P. Leblond and J. Gross. Thyroglobulin formation in the thyroid follicle visualized by the "coated autograph" technique. Endocrinology 1948, 43, 306 324. The use of thinner sections and emulsion coats led to further advances in resolution, and the introduction of tritium was a technical milestone.
High Resolution Autoradiography procedure continues to be used today by molecular biologists to detect RNA molecules in situ, and to study the localization of genes and DNA sequences.
Studies on the turnover of cells Leblond used autoradiography to introduce radioactive precursors of DNA and then examine the renewal and fate of cells of several basic tissue types. He demonstrated for the first time that most cells and tissues in the adult body undergo continued renewal. Using mathematical models and modern methods of quantitation, Leblond and his colleagues estimated with remarkable accuracy the turnover and mitotic rates of numerous cell types. He and his colleagues made fascinating discoveries that resulted in the introduction of "time dimension" to cells and tissues, opening the doors to the understanding of the cell cycle and to the identification of stem cells.
Identification of stem cells in adult organs In the male seminiferous epithelium, studies by Leblond and Yves Clermont in the early 1950s had deciphered how spermatogonia gave rise to spermatocytes, which then differentiated into mature sperm cells in a specific cycle.C.P. Leblond and Y. Clermont. Definition of the stages of the cycle of the seminiferous epithelium of the rat. Ann. NY Acad. Sci. 1952, 55, 548 573.Y. Clermont and C.P. Leblond. Spermiogenesis of man, monkey, ram and other mammals as shown by the "periodic acid Schiff" technique. Am. J. Anat. 1955, 96, 229 250.
To maintain the population of spermatogonia, the seminiferous epithelium was shown to contain a population of stem cells which divided to produce differentiated cells as well as to maintain their own number. As noted in a seminal publication by Leblond, "the reappearance at each cycle of a new dormant cell which acts as the stem cell of spermatocytes is described as the 'Stem Cell Renewal Theory'". This article is the first one in which nests of cells dividing in an adult organ are designated as "stem cells".Y. Clermont and C.P. Leblond. Renewal of spermatogonia in the rat testis. Am. J. Anat. 1953, 93, 475 502.
Leblond and his colleagues also found evidence for the presence of occasional adult stem cells even in tissues which are composed almost entirely of non-dividing cells. In skeletal muscle, the muscle fibers had been shown to exhibit an age-related increase in the number of nuclei.M. Enesco and C.P. Leblond. Increase in cell number as a factor in the growth of the organs and tissues of the young male rat. J. Embryol. Exp. Morphol. 1962, 20, 530 562. His studies showed that muscle satellite cells could be considered to be adult stem cells in muscle fibers.
From the studies of Leblond and his colleagues, it was concluded that the body has three types of cell populations:
"Static cell populations", which are composed of non-dividing cells and include no adult stem cells. These populations have the "stability" formerly attributed to all cells "Expanding cell populations" in which small numbers of adult stem cells exist, and give rise to skeletal fiber nuclei or glial cells of the brain "Renewing cell populations" in which adult stem cells are an essential feature
To mark his 65th birthday in 1975, Leblond was honored at an international symposium on the existence of stem cells in adult tissues; the resulting book, Stem Cells of Renewing Cell Populations, was the first formal, comprehensive account on the subject.Cairnie A.B., Lala P.K. and D.G. Osmond. Stem Cells of renewing Cell Populations Academic Press. N.Y. 1976.
Continuous protein synthesis in living cells When Leblond and his colleagues used 14C-bicarbonate, and then 35S-labeled amino acids to investigate protein synthesis, they were astonished to find that virtually all cells in the body incorporated label.R.C. Greulich and C.P. Leblond. Radioautographic visualization of radio carbon in the organs and tissues of newborn rats following administration of C14 labeled bicarbonate. Anat. Rec. 1953, 115, 559 586.C.P. Leblond, N.B. Everett and B. Simmons. Sites of protein synthesis as shown by radioautography after administration of S35 methionine. Am. J. Anat. 1957, 101, 225 271. This led them to the conclusion, considered heretical at the time, that all cells continually synthesized proteins. This was among the first evidence to replace the Specificity concept with the idea that most cells are multipotential in their functions.