Embryo Project Encyclopedia

"Induction and Patterning of the Primitive Streak, an Organizing Center of Gastrulation in the Amniote," (hereafter referred to as "Induction") examines the mechanisms underlying early amniote gastrulation and the formation of the primitive streak and midline axis. The review, authored by Takashi Mikawa and colleagues at Cornell University Medical College, was published in Developmental Dynamics in 2004. The article primarily discusses chick embryos as a model organism for nonrodent amniote gastrulation, although it intermittently touches on nonamniote gastrulation for comparative purposes. "Induction" attempts to explain the initiation of cell differentiation and embryo organization, one of the most intriguing processes of embryology.

In 1894, William Stewart Halsted published The Results of Operations for the Cure of Cancer of the Breast Performed at the Johns Hopkins Hospital from June, 1889, to January, 1894, in the medical journal Annals of Surgery. In the article, Halsted describes the results from fifty of his operations on women with breast cancer, performed at Johns Hopkins Hospital in Baltimore, Maryland. Those operations involved a surgical procedure Halsted called radical mastectomy, which consists in removing all of the patient’s breast tissue, chest muscle, and underarm lymph nodes. Halsted’s surgery effectively cured breast cancer in a time period when no other effective treatment options were available. The radical mastectomy remained the standard of care from the 1890s to the 1970s as a means of treating a type of reproductive cancer common to women.

William Withey Gull studied paraplegia, anorexia, and hormones as a physician in England during the nineteenth century. In addition to caring for patients, he described the role of the posterior column of the spinal cord in paraplegia, and he was among the first to describe the conditions of anorexia and of hypochondria. He also researched the effects of thyroid hormone deficiencies in women who had malfunctioning thyroid glands. Gull's research on thyroid hormone confirmed that chemicals in the body directly affect health, and he contributed to the foundation of endocrinology, the scientific field for the study of hormones.

"A Diffusible Agent of Mouse Sarcoma, Producing Hyperplasia of Sympathetic Ganglia and Hyperneurotization of Viscera in the Chick Embryo," by Rita Levi-Montalcini and Viktor Hamburger, appeared in 1953 in the Journal of Experimental Zoology. The paper provided the first evidence that nerve growth factor is a diffusible substance. Nerve growth promoting tumors were implanted into developing embryos to determine whether the tumors stimulated growth by direct contact or by a diffusible substance. The tumors were implanted into different parts of the embryo; one set of experiments implanted the tumor directly in the embryo, while another set of experiments placed the tumor on an exterior membrane. The membrane provided a barrier to direct contact with the nervous system, and allowed some chemical interaction between the tumor and the embryo. The tumor stimulated growth in both orientations, demonstrating that nerve growth factor was a chemical agent. The paper ends with two possible conclusions for the mechanism of nerve growth, the tumor may have been directly stimulating the ganglia by a diffusible signal, or it may have reduced the resistance of the chick tissues to the nerve growth. The term "nerve growth factor" is not explicitly used in this paper, and is referred to as a "diffusible agent" or a "growth promoting agent."

Nicole Marthe Le Douarin was one of the first progressive female pioneers of developmental and embryological research. Some of her most notable and ground-breaking work involves grafting quail and chicken embryos together in order to study the developmental fate of each contributing embryo. Le Douarin was born in Brittany, France, on 20 August 1930. As an only child she was inspired by her mother, a school teacher at the time, to develop a passion for learning. According to Le Douarin her father was an open-minded businessman who, likely because she was an only child, raised her much like a boy. In 1944 Le Douarin was forced to move out of her hometown of Lorient and attend a boarding school in Nantes, France, to escape the invasion of German forces during World War II. After the war, she returned to her high school in Lorient, where she received her baccalaureate in 1949. During her last year in Lorient, when she was only seventeen, Douarin met her fianc_. After graduating, and against the wishes of her mother, she moved with him to Paris where they attended the Sorbonne. In 1951, after three years of courtship and university classes together, the couple was married. Le Douarin graduated from the Sorbonne with a degree in the natural sciences in 1954. Instead of immediately continuing to graduate school, she chose to teach science at a local high school and raise a family.

Tissue engineering is a field of regenerative medicine that integrates the knowledge of scientists, physicians, and engineers into the construction or reconstruction of human tissue. Practitioners of tissue engineering seek to repair, replace, maintain, and enhance the abilities of a specific tissue or organ by means of living cells. More often than not stem cells are the form of living cells used in this technology. Tissue engineering is one of the disciplines involved in translating knowledge of developmental biology into the clinical setting. One focus that this field has taken is the understanding of tissue and organ development during embryogenesis, as this knowledge will open avenues to new applications of this technology.

Gastrulation is an early stage in embryo development in which the blastula reorganizes into three germ layers: the ectoderm, the mesoderm, and the endoderm. Gastrulation occurs after cleavage but before neurulation and organogenesis. Ernst Haeckel coined the term; gaster, meaning stomach in Latin, is the root for gastrulation, as the gut is one of the most unique creations of the gastrula.

A node, or primitive knot, is an enlarged group of cells located in the anterior portion of the primitive streak in a developing gastrula. The node is the site where gastrulation, the formation of the three germ layers, first begins. The node determines and patterns the anterior-posterior axis of the embryo by directing the development of the chordamesoderm. The chordamesoderm is a specific type of mesoderm that will differentiate into the notochord, somites, and neural tube. Those structures will later form the vertebral column. In the chick embryo, the node is referred to as Hensen's node because of its discoverer, Viktor Hensen, who first described the node in 1875. The discovery of Hensen's node has helped to answer questions of axis formation and has allowed experimental embryologists to further investigate vertebrate embryonic development.

In 1951 Viktor Hamburger and Howard Hamilton created an embryonic staging series from a combination of photographs and drawings from other researchers. The Hamburger-Hamilton stages are a sequence of images depicting 46 chronological stages in chick development. The images begin with a fertilized egg and end with a fully developed chick. The Hamburger-Hamilton staging series was produced in order to replace a previous chick staging series created in 1900. The earlier attempt lacked specific details and staged the chick embryo by using only morphological characteristics. As chicks were, and still remain, model organisms for experimental embryology, it was important to create a staging series with descriptions for determining the approximate age of a developing chick embryo.