Embryo Project Encyclopedia

Mechanism of Notch Signaling: The image depicts a type of cell signaling, in which two animal cells interact and transmit a molecular signal from one to the other. The process results in the production of proteins, which influence the cells as they differentiate, move, and contribute to embryological development. In the membrane of the signaling cell, there is a ligand (represented by a green oval). The ligand functions to activate a change in a receptor molecule. In the receiving cell, there are receptors; in this case, Notch proteins (represented by orange forks). The Notch proteins are embedded in the receiving cell membrane, and they have at least two parts: an intracellular domain (inside the cell) and the receptor (outside the cell). Once the ligand and receptor bind to each other, a protease (represented by the dark red triangle) can sever the intracellular domain from the rest of the Notch receptor. Inside the nucleus of the receiving cell (represented by the gray area) are the cellês DNA (represented by the multi-colored helices) and its transcription factors (blue rectangles). Transcription factors are proteins that bind to DNA to regulate transcription, the first step in gene expression, which eventually yields proteins or other products. Initially, repressor proteins (represented by a red irregular hexagon) prevent transcription factors from allowing transcription. When the severed Notch receptor intracellular domain reaches the nucleus, it displaces the repressor. The transcription factor can then signal for transcription to occur. 1) There is a Notch receptor protein in the membrane of a receiving cell, and a ligand for this receptor (for example, Delta) in the membrane of the signaling cell. When the ligand binds to the receptor, the intracellular domain of the receptor changes shape. 2) Inside the receiving cell, there are proteases. Once the intracellular domain of the receptor changes shape, the protease can bind to it and shear the intracellular domain away from the rest of the receptor molecule. 3) The severed intracellular domain is shuttled to the receiving cell nucleus. Here, the intracellular domain displaces a repressor protein. This allows a transcription factor to initiate DNA transcription. During transcription, DNA is used as a template to create RNA. Following transcription, the process of translation occurs, which uses RNA as a template to create proteins. These proteins influence the behavior, fate, and differentiation of cells, which contribute to normal embryonic development

Rosalyn Sussman Yalow co-developed the radioimmunoassay (RIA), a method used to measure minute biological compounds that cause immune systems to produce antibodies. Yalow and research partner Solomon A. Berson developed the RIA in the early 1950s at the Bronx Veterans Administration (VA) Hospital, in New York City, New York. Yalow and Berson's methods expanded scientific research, particularly in the medical field, and contributed to medical diagnostics. For this achievement, Yalow received the Nobel Prize in Physiology or Medicine in 1977. The RIA technique is used to measure more than one hundred biochemical substances, including infectious agents, narcotics, and hormones, such as those used to diagnose infertility and hypothyroidism.

In his 1991 article Screening for Congenital Hypothyroidism, Delbert A. Fisher in the US reported on the implementation and impact of mass neonatal screening programs for congenital hypothyroidism (CH) from the early 1970s through 1991. CH is a condition that causes stunted mental and physical development in newborns unless treatment begins within the first three months of the newborn's life. In the early 1970s, regions in Canada and the US had implemented screening programs to diagnose and treat CH as quickly as possible after the infant's birth. By 1991 many other countries had adopted the early screening program, and Fisher estimated that 10 to 12 million newborns per year were tested in the early 1990s. The screening programs, along with physician education and improved screening techniques, such as radioimmunoassay, helped significantly reduce the incidence of abnormal newborn development resulting from untreated congenital hypothyroidism.

'On the Permanent Life of Tissues outside of the Organism' reports Alexis Carrel's 1912 experiments on the maintenance of tissue in culture media. At the time, Carrel was a French surgeon and biologist working at the Rockefeller Institute in New York City. In his paper, Carrel reported that he had successfully maintained tissue cultures, which derived from connective tissues of developing chicks and other tissue sources, by serially culturing them. Among all the tissue cultures Carrel reported, one was maintained for more than two months, whereas previous efforts had only been able to keep tissues in vitro for three to fifteen days. Carrel’s experiments contributed to the development of long-term tissue culture techniques, which were useful in the study of embryology and eventually became instrumental in stem cell research. Despite later evidence to the contrary, Carrel believed that as long as the tissue culture method was accurately applied, tissues kept outside of the organisms should be able to divide indefinitely and have permanent life.

Solomon A. Berson helped develop the radioimmunoassay (RIA) technique in the US during the twentieth century. Berson made many scientific contributions while working with research partner Rosalyn Yalow at the Bronx Veterans Administration (VA) hospital, in New York City, New York. In the more than twenty years that Berson and Yalow collaborated, they refined the procedures for tracing diagnostic biological compounds using isotope labels. In the late 1950s they developed the RIA based on the ability to trace the competition between and ligands, or small molecules that bind to specific sites of other biomolecules, and proteins for the same molecular binding site, a process called competitive binding. Scientists widely used Berson and Yalow's RIA, as these methods permit the use of a minimal sample of blood for accurate measurements of biological molecules such as hormones that cause the production of antibodies. Berson and Yalow's research has advanced the study of physiology, including that of the reproductive system, with particular applications to the diagnosis and treatment of infertility.

Christiane Nusslein-Volhard studied how genes control embryonic development in flies and in fish in Europe during the twentieth and twenty-first centuries. In the 1970s, Nusslein-Volhard focused her career on studying the genetic control of development in the fruit fly Drosophila melanogaster. In 1988, Nusslein-Volhard identified the first described morphogen, a protein coded by the gene bicoid in flies. In 1995, along with Eric F. Wieschaus and Edward B. Lewis, she received the Nobel Prize in Physiology or Medicine for the discovery of genes that establish the body plan and segmentation in Drosophila. Nusslein-Volhard also investigated the genetic control of embryonic development to zebrafish, further generalizing her findings and helping establishing zebrafish as a model organism for studies of vertebrate development.

Rachel L. Carson studied biology at Johns Hopkins University in Maryland and graduated in 1933 with an MA upon the completion of her thesis, The Development of the Pronephros during the Embryonic and Early Larval Life of the Catfish (Ictalurus punctatus). The research that Carson conducted for this thesis project grounded many of the claims and observations she presented in her 1962 book, Silent Spring. This book focused on the environmental dangers of using pesticides against insects and plants deemed invasive, and it received attention from the US government, to such an extent that Carson testified before US congress in Washington D.C., and US President John F. Kennedy appointed a commission to validate her claims.

By 2011, researchers in the US had established that non-invasive blood tests can accurately determine the gender of a human fetus as early as seven weeks after fertilization. Experts predicted that this ability may encourage the use of prenatal sex screening tests by women interested to know the gender of their fetuses. As more people begin to use non-invasive blood tests that accurately determine the sex of the fetus at 7 weeks, many ethical questions pertaining to regulation, the consequences of gender-imbalanced societies, and altered meanings of the parent-child relationship.

Lynn Petra Alexander Sagan Margulis was an American biologist, whose work in the mid-twentieth century focused on cells living together in a mutually advantageous relationship, studied cells and mitochondria in the US during the second half of the twentieth century. She developed a theory for the origin of eukaryotic cells, that proposed two kinds of structures found in eukaryotic cells mitochondria in animals, and plastids in plantsÑwere once free-living bacteria that lived harmoniously and in close proximity to larger cells, a scenario called symbiosis. Margulis proposed that the larger cells eventually engulfed the free-living bacteria, resulting in cells living inside other cells, a situation called endosymbiosis. Margulis'theory became called the serial endosymbiosis theory (SET). Her work contributed to explanations of the evolution and development of life, as eukaryotic cells comprise most multicellular organisms, including their embryos.

Ethical Issues in Human Stem Cell Research: Executive Summary was published in September 1999 by The US National Bioethics Advisory Commission in response to a national debate about whether or not the US federal government should fund embryonic stem cell research. Ethical Issues in Human Stem Cell Research recommended policy to US President William Clinton's administration, which advocated for federal spending on the use of stem research on stem cells that came from embryos left over from in vitro fertilization (IVF) fertility treatments. Although NBAC's proposals never became legislation, the report helped shape public, private, and international discourse on stem cell research policy.