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Somatic Cell Nuclear Transfer in Mammals (1938-2013)
In the second half of the
twentieth century, scientists learned how to clone organisms in some
species of mammals. Scientists have applied somatic cell nuclear transfer to clone human and
mammalian embryos as a means to produce stem cells for laboratory
and medical use. Somatic cell nuclear transfer (SCNT) is a technology applied in cloning, stem cell
research and regenerative medicine. Somatic cells are cells that
have gone through the differentiation process and are not germ
cells. Somatic cells donate their nuclei, which scientists
Format: Articles
Subject: Theories, Technologies, Processes
Stem Cells
According to the US National Institutes of Health (NIH), the standard American source on stem cell research, three characteristics of stem cells differentiate them from other cell types: (1) they are unspecialized cells that (2) divide for long periods, renewing themselves and (3) can give rise to specialized cells, such as muscle and skin cells, under particular physiological and experimental conditions. When allowed to grow in particular environments, stem cells divide many times. This ability to proliferate can yield millions of stem cells over several months.
Format: Articles
Subject: Processes
“Pregnancy Established in an Infertile Patient After Transfer of a Donated Embryo Fertilized In Vitro” (1983), by Alan Trounson, John Leeton, Mandy Besanko, Carl Wood, and Angelo Conti
In 1983, researchers Alan Trounson, John Leeton, Carl Wood, Mandy Besanko, and Angelo Conti published the article “Pregnancy Established in an Infertile Patient After Transfer of a Donated Embryo Fertilized In Vitro” in The British Medical Journal. In the article, the authors discuss one of the first successful experiments using in vitro fertilization, or IVF, with the use of a human donor embryo at the Monash University and Queen Victoria Medical Center in Melbourne, Australia.
Format: Articles
Subject: Publications, Publications, Reproduction, Processes
Pearl Luella Kendrick (1890–1980)
Pearl Luella Kendrick researched prevention for pertussis, commonly known as whooping cough, in Grand Rapids, Michigan, during the mid-1900s. Pertussis is a respiratory disease that mainly affects infants and young children. During the 1920s, pertussis was responsible for more deaths in children in the United States than any other disease. In the 1930s, Kendrick created one of the first pertussis vaccines that underwent large-scale clinical trials.
Format: Articles
Subject: People, Publications, Processes
The Role of the Notch signaling pathway in Somitogenesis
Among other functions, the Notch signaling pathway contributes to the development of somites in animals. It involves a cell signaling mechanism with a wide range of functions, including cellular differentiation, and the formation of the embryonic structures (embryogenesis). All multicellular animals use Notch signaling, which is involved in the development, maintenance, and regeneration of a range of tissues. The Notch signaling pathways spans two cells, and consists of receptor proteins, which cross one cell's membrane and interacts with proteins on adjacent cells, called ligands.
Format: Articles
Hensen's Node
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.
Format: Articles
Subject: Processes
Umbilical Cord Blood Stem Cells (UCBSC)
Umbilical cord blood (UCB) stem cells are hematopoietic stem cells (HSC) that are recovered from the blood of the umbilical cord and placenta after birth. Umbilical cord blood is rich in cells that express the CD34 molecule, a surface protein that identifies cells as stem cells. Prior to the discovery of UCB stem cells, it was standard procedure to discard the umbilical cord and placenta; now much effort is devoted to raising public awareness and to encouraging people to store or donate cord blood.
Format: Articles
Subject: Processes, Reproduction
Gastrulation in Gallus gallus (Domestic Chicken)
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.
Format: Articles
Subject: Processes
The Carapacial Ridge of Turtles
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.
Format: Articles
Subject: Processes
Post-Coital Oral Emergency Contraception
Post-coital oral emergency contraception is used for the prevention of pregnancy after intercourse. The contraception comes in the form of pills, often collectively referred to as morning-after pills. Post-coital use of morning-after pills separates them from traditional contraception which is either a continual preventative process, such as the birth control pill, or used during intercourse, such as condoms.
Format: Articles
Subject: Processes, Reproduction
The Use of Morphine and Scopolamine to Induce Twilight Sleep
In 1907, researchers Bernhardt Kronig and Carl Gauss combined the drugs morphine and scopolamine to induce twilight sleep in women during childbirth. Physicians in the early twentieth century in Germany used twilight sleep, Dammerschlaf, to cause women to enter a state of consciousness in which they felt no pain and did not remember giving birth. Twilight sleep was associated with increased use of forceps during delivery, prolonged labor, and increased risk of infant suffocation.
Format: Articles
Subject: Processes
Reassessment of Carrel's Immortal Tissue Culture Experiments
In the 1910s, Alexis Carrel, a French surgeon and biologist, concluded that cells are intrinsically immortal. His claim was based on chick-heart tissue cultures in his laboratory that seemed to be able to proliferate forever. Carrel's ideas about cellular immortality convinced his many contemporaries that cells could be maintained indefinitely. In the 1960s, however, Carrel's thesis about cell immortality was put into question by the discovery that human diploid cells can only proliferate for a finite period.
Format: Articles
Mechanistic Realization of the Turtle Shell
Turtle morphology is unlike that of any other vertebrate. The uniqueness of the turtle's bodyplan is attributed to the manner in which the turtle's ribs are ensnared within its hard upper shell. The exact embryological and genetic mechanisms underpinning this peculiar anatomical structure are still a matter of debate, but biologists agree that the evolution of the turtle shell lies in the embryonic development of the turtle.
Format: Articles
Subject: Processes
Circulatory Changes at Birth
When placental mammals are born their circulatory systems undergo radical changes as the newborns are prepared for independent life. The lungs are engaged, becoming the primary source of fresh oxygen, replacing the placental barrier as a means for blood-gas exchange.
Format: Articles
Subject: Processes
The Notch Signaling Pathway in Embryogenesis
The Notch signaling pathway is a mechanism in animals by which adjacent cells communicate with each other, conveying spatial information and genetic instructions for the animal's development. All multicellular animals utilize Notch signaling, which contributes to the formation, growth, and development of embryos (embryogenesis). Notch signaling also contributes to the differentiation of embryonic cells into various types of cells into various types of cells, such as neurons.
Format: Articles
Subject: Processes
Hedgehog Signaling Pathway
The hedgehog signaling pathway is a mechanism that directs the development of embryonic cells in animals, from invertebrates to vertebrates. The hedgehog signaling pathway is a system of genes and gene products, mostly proteins, that convert one kind of signal into another, called transduction. In 1980, Christiane Nusslein-Volhard and Eric F. Wieschaus, at the European Molecular Biology Laboratory in Heidelberg, Germany, identified several fruit fly (Drosophila melanogaster) genes.
Format: Articles
Subject: Processes
The French Flag Model
The French flag model represents how embryonic cells receive and respond to genetic information and subsequently differentiate into patterns. Created by Lewis Wolpert in the late 1960s, the model uses the French tricolor flag as visual representation to explain how embryonic cells can interpret genetic code to create the same pattern even when certain pieces of the embryo are removed. Wolpert's model has provided crucial theoretical framework for investigating universal mechanisms of pattern formation during development.
Format: Articles
“Transfer of a Human Zygote” (1973), by David De Kretzer, Peter Dennis, Bryan Hudson, John Leeton, Alexander Lopata, Ken Outch, James Talbot, and Carl Wood
On 29 September 1973, researchers David De Kretzer, Peter Dennis, Bryan Hudson, John Leeton, Alexander Lopata, Ken Outch, James Talbot, and Carl Wood published “Transfer of a Human Zygote,” in The Lancet. In the article, the authors describe an experiment that resulted in one of the first pregnancies established via in vitro fertilization, or IVF. Prior to the article’s publication in 1973, there was no published evidence demonstrating whether IVF treatment would work in humans, although evidence existed showing that IVF worked in other mammals for breeding purposes.
Format: Articles
Subject: Publications, Processes
Homeobox Genes and the Homeobox
Homeobox genes are a cluster of regulatory genes that are spatially and temporally expressed during early embryological development. They are interesting from both a developmental and evolutionary perspective since their sequences are highly conserved and shared across an enormously wide array of living taxa.
Format: Articles
Subject: Processes
The Process of Implantation of Embryos in Primates
Implantation is a process in which a developing embryo, moving as a blastocyst through a uterus, makes contact with the uterine wall and remains attached to it until birth. The lining of the uterus (endometrium) prepares for the developing blastocyst to attach to it via many internal changes. Without these changes implantation will not occur, and the embryo sloughs off during menstruation. Such implantation is unique to mammals, but not all mammals exhibit it.
Format: Articles
Subject: Processes
The Meselson-Stahl Experiment (1957–1958), by Matthew Meselson and Franklin Stahl
In an experiment later named for them, Matthew Stanley Meselson and Franklin William Stahl in the US demonstrated during the 1950s the semi-conservative replication of DNA, such that each daughter DNA molecule contains one new daughter subunit and one subunit conserved from the parental DNA molecule. The researchers conducted the experiment at California Institute of Technology (Caltech) in Pasadena, California, from October 1957 to January 1958.
Format: Articles
Subject: Processes, Experiments
The Development of Silicone Breast Implants for Use in Breast Augmentation Surgeries in the United States
In the 1960s, two plastic surgeons from the United States, Thomas Dillon Cronin and Frank Judson Gerow, collaborated with the Dow Corning Corporation, which specialized in silicone products, to create the first silicone breast implant. Surgeons used the implant, named the Cronin-Gerow implant, to improve the look of a woman’s breasts, by correcting for asymmetry, augmenting the size, or creating a more uplifted profile.
Format: Articles
Subject: Technologies, Processes
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