Embryo Project Encyclopedia Articles

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.

The endothelium is the layer of cells lining the blood vessels in animals. It weighs more than one kilogram in adult humans, and it covers a surface area of 4000 to 7000 square meters. The endothelium is the cellular interface between the circulating blood and underlying tissue. As the medium between these two sets of tissues, endothelium is part of many normal and disease processes throughout the body. The endothelium responds to signals from its surrounding environment to help regulate functions like the resistance that blood vessels need to pump blood through the body (vasomotor tone), the policing of substances trying to enter or exit the blood vessel (blood vessel permeability), and the ability of blood to clot (hemostasis). In addition to diseases like atherosclerosis, endothelium has been indicated as a component in pathologies like cancer, asthma, diabetes, hepatitis, multiple sclerosis, and sepsis. The shape, size, and appearance of endothelial cells, called their phenotypes, vary depending upon which part of the body the cells are from, a property called phenotypic heterogeneity. The endothelium, its properties, and its responses to stimuli are governed largely by the local environment of the cells.

In 2004, a team of researchers at Tufts-New England
Medical Center in Boston, Massachusetts, investigated the fetal
cells that remained in the maternal blood stream after pregnancy.
The results were published in Transfer of Fetal Cells with
Multilineage Potential to Maternal Tissue. The team working on that
research included Kiarash Khosrotehrani, Kirby L. Johnson, Dong
Hyun Cha, Robert N. Salomon, and Diana W. Bianchi. The researchers
reported that the fetal cells passed to a pregnant woman during
pregnancy could develop into multiple cell types in her organs. They
studied these differentiated fetal cells in a cohort of women
fighting different diseases. The researchers found that the fetal
cells in the women differentiated into different cell types under
the influence of maternal tissues, and that those differentiated
cells concentrated in the tissue surrounding diseased tissues.
According to the team, this response could be a therapeutic response
to the disease in the once pregnant woman. The research indicated the long
lasting effects of pregnancy in a woman's body.

At the turn of the twentieth century, Edmund B. Wilson
performed experiments to show where germinal
matter was located in molluscs. At Columbia University in New York City,
New York, Wilson studied what causes cells to differentiate during
development. In 1904 he conducted his experiments on molluscs, and he modified the
theory about the location of germinal matter in the succeeding years. Wilson and others modified the
theory of germinal localization to accommodate results that showed
the significance of chromosomes in development and heredity.

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.

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers. Animals that have only two germ layers develop open digestive cavities. In contrast, the evolutionary development of the mesoderm allowed in animals the formation of internal organs such as stomachs and intestines (viscera).

Neurocristopathies are a class of pathologies in vertebrates,
including humans, that result from abnormal expression, migration,
differentiation, or death of neural crest cells (NCCs) during embryonic development. NCCs are cells
derived from the embryonic cellular structure called the neural crest.
Abnormal NCCs can cause a neurocristopathy by chemically affecting the
development of the non-NCC tissues around them. They can also affect the
development of NCC tissues, causing defective migration or
proliferation of the NCCs. There are many neurocristopathies
that affect many different types of systems. Some neurocristopathies
result in albinism (piebaldism) and cleft palate in humans. Various
pigment, skin, thyroid, and hearing disorders, craniofacial and heart
abnormalities, malfunctions of the digestive tract, and tumors can be
classified as neurocristopathies. This classification ties a variety of
disorders to one embryonic origin.

Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.

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.