Embryo Project Encyclopedia Articles

Thalidomide is a sedative drug introduced to European markets on 1 October 1957 after extensive testing on rodent embryos to ensure its safety. Early laboratory tests in rodent populations showed that pregnant rodents could safely use it, so doctors prescribed Thalidomide to treat morning sickness in pregnant women. However, in humans Thalidomide interfered with embryonic and fetal development in ways not observed in rodent tests. Pregnant women who take Thalidomide are at grater than normal risk for spontaneous abortion and for giving birth to children with developmental anomalies such as shortened, absent, or extra limbs, as well as a variety of heart, ear, and internal organ defects. The failure of rodent models to inform scientists of Thalidomide's teratogenicity in humans ignited debate about the proper use of cross-species testing during drug development.

Vitamin A (retinol) is an essential vitamin in the daily functioning of human beings that helps regulate cellular differentiation of epithelial tissue. Studies have shown that an excess of vitamin A can affect embryonic development and result in teratogenesis, or the production of birth defects in a developing embryo. Excess intake of vitamin A and retinoids by pregnant women often results malformations to fetuses' skulls, faces, limbs, eyes, central nervous system. Additionally, doctors often use derivatives of vitamin A, known as retinoids, as medicine to treat a number of skin conditions and carcinomas, the most common form of human cancers.

Dizhou Tong, also called Ti Chou Tung, studied marine animals and helped introduce and organize experimental embryology in China during the twentieth century. He introduced cellular nuclear transfer technology to the Chinese biological community, developed methods to clone organisms from many marine species, and investigated the role of cytoplasm in early development. Tong's administrative and scientific leadership in the fields of marine, cellular, and developmental biology contributed to China's experimental embryology research programs.

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.'

Andrew Francis Dixon studied human anatomy and egg cells at the turn of the twentieth century in Ireland and Great Britain. Dixon studied the sensory and motor nervous system of the face, the cancellous bone tissue of the femur, supernumerary kidneys, and the urogenital system. In 1927 Dixon described a mature human ovarian follicle. This follicle, Dixon noted, contained an immature human egg cell (oocyte) with a visible first polar body and the beginnings of the second polar body. Dixon's work helped researchers describe many of the items found in follicles during the production of oocytes, and it helped them identify when, where, and how those items were produced. Based upon his descriptions, later researchers further described polar bodies and investigated their functions.

Thalidomide, a drug capable of causing fetal abnormalities (teratogen), has caused greater than ten thousand birth defects worldwide since its introduction to the market as a pharmaceutical agent. Prior to discovering thalidomide's teratogenic effects in the early 1960s, the US Food and Drug Administration (FDA) did not place regulations on drug approval or monitoring as it later did. By 1962, approximately 20,000 patients in the US had taken thalidomide as part of an unregulated clinical trial before any actions were taken to stop thalidomide's distribution. Due to thalidomide's effects on fetuses, both nationally and abroad, the US Congress passed the 1962 Kefauver-Harris Amendments to the 1938 Food, Drug, and Cosmetic Act. These amendments imposed guidelines for the process of drug approval in the US and required that a drug be safe as well as effective before it could be approved and marketed. Thalidomide also influenced the FDA's creation of pregnancy categories; a ranking of drugs based on their effects on reproduction and pregnancy. Thalidomide motivated the laws on regulating and monitoring drugs developed in the US and by the FDA in the twentieth and twenty-first centuries.

St. George Jackson Mivart studied animals and worked in England during the nineteenth century. He also proposed a theory of organismal development that he called individuation, and he critiqued Charles Darwin's argument for evolution by natural selection. His work on prosimians, a group of primates excluding apes and monkeys, helped scientists better investigate the Primate group. In his work On the Genesis of Species, Mivart argued that Darwin's theory couldn't explain how specific organismal forms developed and varied, explanations Mivart argued were necessary before Darwin could invoke the mechanism of natural selection to explain the evolution of species. To provide those explanations Mivart proposed theories of individuation and of instinct.

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).

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.