Embryo Project Encyclopedia

'On the Permanent Life of Tissues outside of the Organism' reports Alexis Carrel's 1912 experiments on the maintenance of tissue in culture media. At the time, Carrel was a French surgeon and biologist working at the Rockefeller Institute in New York City. In his paper, Carrel reported that he had successfully maintained tissue cultures, which derived from connective tissues of developing chicks and other tissue sources, by serially culturing them. Among all the tissue cultures Carrel reported, one was maintained for more than two months, whereas previous efforts had only been able to keep tissues in vitro for three to fifteen days. Carrel’s experiments contributed to the development of long-term tissue culture techniques, which were useful in the study of embryology and eventually became instrumental in stem cell research. Despite later evidence to the contrary, Carrel believed that as long as the tissue culture method was accurately applied, tissues kept outside of the organisms should be able to divide indefinitely and have permanent life.

The p53 protein acts as a pivotal suppressor of inappropriate cell proliferation. By initiating suppressive effects through induction of apoptosis, cell senescence, or transient cell-cycle arrest, p53 plays an important role in cancer suppression, developmental regulation, and aging. Its discovery in 1979 was a product of research into viral etiology and the immunology of cancer. The p53 protein was first identified in a study of the role of viruses in cancer through its ability to form a complex with viral tumor antigens. In the same year, an immunological study of cancer also found p53 due to its immunoreactivity with tumor antisera. Although a series of studies found p53 through various routes, and various researchers called it different names, it was eventually confirmed that they had all encountered the same protein, p53.

In a series of experiments between 1960 and 1965, Robert Geoffrey Edwards discovered how to make mammalian egg cells, or oocytes, mature outside of a female's body. Edwards, working at several research institutions in the UK during this period, studied in vitro fertilization (IVF) methods. He measured the conditions and timings for in vitro (out of the body) maturation of oocytes from diverse mammals including mice, rats, hamsters, pigs, cows, sheep, and rhesus monkeys, as well as humans. By 1965, he manipulated the maturation of mammalian oocytes in vitro, and discovered that the maturation process took about the same amount of time as maturation in the body, called in vivo. The timing of human oocyte maturation in vivo, extrapolated from Edwards's in vitro study, helped researchers calculate the timing for surgical removal of human eggs for IVF.

In the early 1960s, John W. Saunders Jr., Mary T. Gasseling, and Lilyan C. Saunders in the US investigated how cells die in the developing limbs of chick embryos. They studied when and where in developing limbs many cells die, and they studied the functions of cell death in wing development. At a time when only a few developmental biologists studied cell death, or apoptosis, Saunders and his colleagues showed that researchers could use embryological experiments to uncover the causal mechanisms of apotosis. The researchers published many of their results in the 1962 paper 'Cellular death in morphogenesis of the avian wing.'

German embryologist Viktor Hamburger came to the US in 1932 with a fellowship provided by the Rockefeller Foundation. Hamburger started his research in Frank Rattray Lillie's laboratory at the University of Chicago. His two-year work on the development of the central nervous system (CNS) in chick embryos was crystallized in his 1934 paper, "The Effects of Wing Bud Extirpation on the Development of the Central Nervous System in Chick Embryos," published in The Journal of Experimental Zoology. Hamburger was able to use the microsurgical techniques that he had learned from Hans Spemann to show how wing buds influence the development of the CNS in chick embryos. This paper is one of several among Hamburger's important studies on chick embryos and represents the empirical and theoretical cornerstone for his further research on central-peripheral relations in the development of the nervous system.

An important question throughout the history of embryology is whether the formation of a biological structure is predetermined or shaped by its environment. If both intrinsic and environmental controls occur, how exactly do the two processes coordinate in crafting specific forms and functions? When Viktor Hamburger started his PhD study in embryology in the 1920s, few neuroembryologists were investigating how the central neurons innervate peripheral organs. As Hamburger began his research, he had no clue that central-peripheral relations in the development of the central nervous system (CNS) would become one of his major interests for the next seventy-five years. In fact, this research trajectory would lead him to discover programmed cell death as a pivotal mechanism mediating central-peripheral relations, as well as to Nobel-Prize-winning work on nerve growth factors (NGF).

Richard A. Lockshin's 1963 PhD dissertation on cell death in insect metamorphosis was conducted under the supervision of Harvard insect physiologist Carroll M. Williams. Lockshin and Williams used this doctoral research as the basis for five articles, with the main title "Programmed Cell Death," that were published between 1964 and 1965 in the Journal of Insect Physiology. These articles examine the cytological processes, neuronal and endocrinal controls, and the influence of drugs on the mechanism of cell death observed in pupal muscle structures of the American silkmoth. Those muscle structures disappeared right after the completion of adult development. Several scientists have credited this series of articles as introducing the now standard term "programmed cell death." Among the five articles, "Endocrine Potentiation of the Breakdown of the Intersegmental Muscles of Silkmoths" (abbreviated hereafter as "Endocrine Potentiation") was published first and has been cited the most often. The article suggests that the endocrinal conditions at the beginning of the adult development are necessary, but not sufficient, for precisely scheduling three weeks later the cell death activities in the pupal intersegmental muscles of American silkmoths. The research was among the first to attempt to pinpoint the role of hormones in regulating cell death, a process integral to development.

Robert Geoffrey Edwards, a British developmental biologist at University of Cambridge, began exploring human in vitro fertilization (IVF) as a way to treat infertility in 1960. After successfully overcoming the problem of making mammalian oocytes mature in vitro in 1965, Edwards began to experiment with fertilizing matured eggs in vitro. Collaborating with other researchers, Edwards eventually fertilized a human egg in vitro in 1969. This was a huge step towards establishing human IVF as a viable fertility treatment. During the four years in which Edwards experimented with IVF, he experienced many setbacks. These failures in fertilizing oocytes in vitro, however, contributed to the understanding of how fertilization did or did not happen, which was sometimes different from established dogmas. Edwards also collaborated with gynecologist and surgeon Patrick Christopher Steptoe to study sperm capacitation, which became the overture that heralded a series of successes for the team, culminating in the generation of the first test-tube baby Louise Joy Brown in 1978.

The biomedical accomplishment of human in vitro fertilization and embryo transfer (IVF-ET) took years to become the successful technique that presently enables infertile couples to have their own children. In 1969, more than ten years after the first attempts to treat infertilities with IVF technologies, the British developmental biologist Robert Geoffrey Edwards fertilized human oocytes in a Petri dish for the first time. In 1970, Edwards and his research partner, gynecologist and surgeon Patrick Christopher Steptoe, started working with human patients with complicated and individualized gynecological conditions. It took Edwards and Steptoe another eight years of modifying medical procedures, as well as dealing with the ups and downs of funding situations and public opinions, before they could celebrate birth of the first baby conceived through IVF-ET in 1978.

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.