In 2006, Kazutoshi Takahashi and Shinya Yamanaka reprogrammed mice fibroblast cells, which can produce only other fibroblast cells, to become pluripotent stem cells, which have the capacity to produce many different types of cells. Takahashi and Yamanaka also experimented with human cell cultures in 2007. Each worked at Kyoto University in Kyoto, Japan. They called the pluripotent stem cells that they produced induced pluripotent stem cells (iPSCs) because they had induced the adult cells, called differentiated cells, to become pluripotent stem cells through genetic manipulation. Yamanaka received the Nobel Prize in Physiology or Medicine in 2012, along with John Gurdon, as their work showed scientists how to reprogram mature cells to become pluripotent. Takahashi and Yamanaka's 2006 and 2007 experiments showed that scientists can prompt adult body cells to dedifferentiate, or lose specialized characteristics, and behave similarly to embryonic stem cells (ESCs).
The Cell in Development and Inheritance, by Edmund Beecher Wilson, provided a textbook introduction to cell biology for generations of biologists in the twentieth century. In his book, Wilson integrated information about development, inheritance, chromosomes, organelles, and the structure and functions of cells. First published in 1896, the book started with 371 pages, grew to 483 pages in the second edition that appeared in 1900, and expanded to 1,231 pages by the third and final edition in 1925. Wilson dedicated the book to the cell biologist Theodor Boveri, whose work established the roles of chromosomes in cell division. With its explanations and many illustrations and diagrams, The Cell in Development and Inheritance enabled embryologists to better understand development in terms of cell structure and function.
Friedrich Leopold August Weismann published Das Keimplasma: eine Theorie der Vererbung (The Germ-Plasm: a Theory of Heredity, hereafter The Germ-Plasm) while working at the University of Freiburg in Freiburg, Germany in 1892. William N. Parker, a professor in the University College of South Wales and Monmouthshire in Cardiff, UK, translated The Germ-Plasm into English in 1893. In The Germ-Plasm, Weismann proposed a theory of heredity based on the concept of the germ plasm, a substance in the germ cell that carries hereditary information. The Germ-Plasm compiled Weismann's theoretical work and analyses of other biologists' experimental work in the 1880s, and it provided a framework to study development, evolution and heredity. Weismann anticipated that the germ-plasm theory would enable researchers to investigate the functions and material of hereditary substances.
In an effort to develop tissue culture techniques for long-term tissue cultivation, French surgeon and biologist Alexis Carrel, and his associates, produced and maintained a series of chick heart tissue cultures at the Rockefeller Institute in New York City. From 1912 to 1946, this series of chick heart tissue cultures remained alive and dividing. Since the duration of this culture greatly exceeded the normal chick life span, the cells were deemed immortal. Although this conclusion was challenged by further experiments in the 1960s, the publicity surrounding the immortal chick heart tissue significantly influenced the concept of cell immortality and cellular aging from the 1920s through the 1960s. Carrel's experiment convinced many biologists to accept immortality as an intrinsic property of all cells, not just the cell line through which genetic material is passed to offspring, called the germ line. Consequently, the phenomenon of cellular aging was regarded not as an intrinsic characteristic, but was attributed to external factors such as the accumulation of waste products within the cell.
In the July 2007 issue of Nature, Keisuke Okita, Tomoko Ichisaka, and Shinya Yamanaka added to the new work on induced pluripotent stem cells (iPSCs) with their "Generation of Germline-Competent Induced Pluripotent Stem Cells" (henceforth abbreviated "Generation"). The authors begin the paper by noting their desire to find a method for inducing somatic cells of patients to return to a pluripotent state, a state from which the cell can differentiate into any type of tissue but cannot form an entire organism. If this is made possible, the authors claim, the ethical controversy surrounding the use of embryonic stem cells (ES cells) and the dangers of patient rejection of donated ES cells could be bypassed completely.
Through various studies developmental biologists have been able to determine that the muscles of the back, ribs, and limbs derive from somites. Somites are blocks of cells that contain distinct sections that diverge into specific types (axial or limb) of musculature and are an essential part of early vertebrate development. For many years the musculature of vertebrates was known to derive from the somites, but the exact developmental lineage of axial and limb muscle progenitor cells remained a mystery until Nicole Le Douarin and Charles P. Ordahl published "Two Myogenic Lineagues within the Developing Somite" in 1991. This paper describes their experiment, which used chick-quail chimeras to demonstrate the exact lineage of the limb and back musculature.
Somites are blocks of mesoderm that are located on either side of the neural tube in the developing vertebrate embryo. Somites are precursor populations of cells that give rise to important structures associated with the vertebrate body plan and will eventually differentiate into dermis, skeletal muscle, cartilage, tendons, and vertebrae. Somites also determine the migratory paths of neural crest cells and of the axons of spinal nerves.
On 2 December 2007, Science published a report on creating human induced pluripotent stem (iPS) cells from human somatic cells: "Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells." This report came from a team of Madison, Wisconsin scientists: Junying Yu, Maxim A. Vodyanik, Kim Smuga-Otto, Jessica Antosiewicz-Bourget, Jennifer L. Frane, Shulan Tian, Jeff Nie, Gudrun A. Jonsdottir, Victor Ruotti, Ron Stewart, Igor I. Slukvin, and James A. Thomson. Earlier that year Shinya Yamanaka at Kyoto University, Japan published a similar paper,"Generation of Germline-Competent Induced Pluripotent Stem Cells," in Nature. Both papers independently identified four genes used to reprogram human somatic cells to pluripotent stem cells, which are cells that have the ability to develop into any specialized cell type making up the body. The reprogrammed somatic cells were referred to as iPS cells and they exhibit fundamental qualities of human embryonic stem (ES) cells.