Embryo Project Encyclopedia

In 1861, William John Little published, “On The Influence of Abnormal Parturition, Difficult Labors, Premature Birth, and Asphyxia Neonatorum, on the Mental and Physical Condition of the Child, Especially in Relation to Deformities,” hereafter “Abnormal Parturition,” in the Transactions of the Obstetrical Society of London. In the article, Little discussed the causes and types of what he refers to as abnormal births, and theorized how those births affect an infant’s likelihood of exhibiting a deformity. Little defined abnormal births as those involving an atypical maternal or fetal presentation, such as a slow birthing process or a fetus exiting the birth canal feet first rather than head first. In his article, Little published one of the first definitional frameworks to describe a condition causing rigidity and stiffness in the limbs that is often associated with birth-related trauma, which was then called Little’s disease, but is modernly known as spastic Cerebral Palsy.

The March of Dimes Foundation, or the March of Dimes, is a non-profit organization headquartered in Arlington, Virginia, focused on the health of pregnant women and infants in the US. Former United States president Franklin Delano Roosevelt founded the March of Dimes, then called the National Foundation for Infantile Paralysis, in 1938 to address polio. Polio is a viral illness that infects the spinal cord and may lead to paralysis. Roosevelt contracted polio in 1921, which left him permanently paralyzed from the waist down. During the 1960s, after scientists introduced polio vaccines, March of Dimes shifted its focus to prevent preterm birth and birth defects. As a non-profit organization, March of Dimes provides community service, funds for research, and efforts to educate the public about preterm birth and birth defects. While March of Dimes’ original goal was to help reduce the spread of polio in the US, it was also one of the first organizations to lead a campaign to prevent birth defects and infant mortality.

William John Little was one of the first orthopedic surgeons to research congenital malformations and their causes in the nineteenth century and presented preliminary research on a condition modernly known as cerebral palsy, a condition of varying severity that affects a person’s ability to move. Little worked throughout the United Kingdom for the majority of the time he practiced medicine, and eventually founded one of the first orthopedic infirmaries, the Royal Orthopedic Hospital in London, England. Throughout his career, Little studied congenital malformations, which are medical conditions inherited before birth, as well as how certain medical circumstances during delivery affect the neonate. In 1861, he described a condition with motor, behavioral, and cognitive irregularities in neonates, linked with oxygen deprivation during birth. Little’s research on that condition, originally called Little’s disease, and modernly, spastic cerebral palsy, was one of the first accounts of cerebral palsy in infants.

Between February 1969 and August 1970 Edward Kollar and Grace Baird, from the University of Chicago in Chicago, Illinois, published three papers that established the role of the mesenchyme in tooth induction. Drawing upon a history of using tissue interactions to understand differentiation, Kollar and Baird designed their experiments to understand how differentiated structures become specified. Their work overturned a widely accepted model that epithelium controls the identity of the structure, a phenomenon called structural specificity. Interactions between epithelium and mesenchyme control the development and differentiation of many parts during embryonic development, including structures like the gastrointestinal tract and hair. Thus, the realization that mesenchyme drives induction and differentiation during epithelio-mesenchymal interactions had far-reaching effects.

Sir John Bertrand Gurdon further developed nuclear transplantation, the technique used to clone organisms and to create stem cells, while working in Britain in the second half of the twentieth century. Gurdon's research built on the work of Thomas King and Robert Briggs in the United States, who in 1952 published findings that indicated that scientists could take a nucleus from an early embryonic cell and successfully transfer it into an unfertilized and enucleated egg cell. Briggs and King also concluded that a nucleus taken from an adult cell and similarly inserted into an unfertilized enucleated egg cell could not produce normal development. In 1962, however, Gurdon published results that indicated otherwise. While Briggs and King worked with Rana pipiens frogs, Gurdon used the faster-growing species Xenopus laevis to show that nuclei from specialized cells still held the potential to be any cell despite its specialization. In 2012, the Nobel Prize Committee awarded Gurdon and Shinya Yamanaka its prize in physiology and medicine for for their work on cloning and pluripotent stem cells.

The Spemann-Mangold organizer, also known as the Spemann organizer, is a cluster of cells in the developing embryo of an amphibian that induces development of the central nervous system. Hilde Mangold was a PhD candidate who conducted the organizer experiment in 1921 under the direction of her graduate advisor, Hans Spemann, at the University of Freiburg in Freiburg, German. The discovery of the Spemann-Mangold organizer introduced the concept of induction in embryonic development. Now integral to the field of developmental biology, induction is the process by which the identity of certain cells influences the developmental fate of surrounding cells. Spemann received the Nobel Prize in Medicine in 1935 for his work in describing the process of induction in amphibians. The Spemann-Mangold organizer drew the attention of embryologists, and it spurred numerous experiments on the nature of induction in many types of developing embryos.

Telomerase is an enzyme that regulates the lengths of telomeres in the cells of many organisms, and in humans it begins to function int the early stages of embryonic development. Telomeres are repetitive sequences of DNA on the ends of chromosomes that protect chromosomes from sticking to each other or tangling. In 1989, Gregg Morin found that telomerase was present in human cells. In 1996, Woodring Wright and his team examined human embryonic cells and found that telomerase was active in them. Scientists manipulate telomerase in cells to give cells the capacity to replicate infinitely. Telomerase is also necessary for stem cells to replicate themselves and to develop into more specialized cells in embryos and fetuses.

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.

Two main elements characterize the skeletal morphology of turtles: the carapace and the plastron. For a turtle, the carapacial ridge begins in the embryo as a bulge posterior to the limbs but on both sides of the body. Such outgrowths are the first indication of shell development in turtle embryos. While the exact mechanisms underpinning the formation of the carapacial ridge are still not entirely known, some biologists argue that understanding these embryonic mechanisms is pivotal to explaining both the development of turtles and their evolutionary history.

Methylmercury (MeHg) is an organic form of mercury that can damage the developing brains of human fetuses. Women who consume methylmercury during pregnancy can bear children who have neurological issues because methylmercury has toxic effects on the nervous system during embryonic development. During the third week of gestation, the human nervous system begins to form in the embryo. During this gestational period, the embryo's nervous system is particularly susceptible to the influence of neurotoxins like methylmercury that can result in abnormalities. Furthermore, the fetal brain can incur damage despite the lack of signs of poisoning in the pregnant woman. In children, defects due to methylmercury can result in deficits in attention, behavior, cognition, and motor skills.