Embryo Project Encyclopedia

Walter Jakob Gehring discovered the homeobox, a DNA segment found in a specific cluster of genes that determine the body plan of animals, plants, and fungi. Gehring identified the homeobox in 1983, with the help of colleagues while isolating the Antennapedia (Antp) gene in fruit flies (Drosophila) at the University of Basel in Basel, Switzerland. Hox genes, a family of genes that have the homeobox, determine the head-to-tail (anterior-posterior) body axis of both vertebrates and invertebrates. Gehring also identified the homeobox-containing Pax-6 gene as the master control gene in eye development of Drosophila, the same gene that, when mutated or absent in humans, leads to aniridia, or lack of the iris, in humans. Gehring's work with the homeobox suggested to biologists that widely different species share a similar and evolutionarily conserved genetic pathway that controls the development of overall body plans, from fruit flies to humans.

Edwin Stephen Goodrich studied the structures of animals in England during the nineteenth and twentieth centuries. Goodrich studied how animals develop to identify their parts and to establish the evolutionary relationships between different species. Goodrich established that body structures can shift their positions relative to an organism's body during evolution, and he hypothesized that body structures can share ancestry (homology) between organisms of different species, even without identical body placement. Goodrich claimed that any given characteristic of an organism results from both genetic and external sources.

Theodora Colborn studied how chemicals affect organisms as they develop and reproduce during the twentieth and twenty first centuries in the US. By the 1940s, researchers had reported that chemicals from agricultural and industrial processes affected how wild organisms developed, but in 1991, Colborn organized the Wingspread Conference in Racine, Wisconsin, at which a group of scientists classed these chemicals as environmentally harmful substances. Colborn and her colleagues called those chemicals endocrine disruptors, as they mimic or block the body's endocrine system. After scientists identified these chimicals and showed that they harm humans and wildlife, US Congress passed several acts to regulate these chemicals and to protect both wildlife and humans from their harmful effects.

In the early 2000s, Manjong Han, Xiaodang Yang, Jennifer Farrington, and Ken Muneoka investigated how genes and proteins in fetal mice (Mus musculus) influenced those fetal mice to regenerate severed toes at Tulane University in New Orleans, Louisiana. The group used hind limbs from mice to show how the gene Msx1 (Homeobox 7) functions in regenerating amputated digits. The researchers showed that in the process of regenerating digit tips, Msx1 genes make products that regulate or influence other genes, such as the Bone Morphogenetic Protein 4 gene (BMP4 gene), to produce proteins, such as the BMP4 proteins. The researchers also showed that BMP4 proteins, which are produced from the BMP4 gene, function in tissues during the process of limb development. Furthermore, while Msx1 genes regulate other genes during the process of regeneration, they don't produce proteins otherwise needed to organize cells in the regeneration of digit tissues. The group published their results in 2003 as Digit Regeneration Is Regulated by Msx1 and BMP4 in Fetal Mice.

Diethylstilbestrol (DES) is an artificially created hormone first synthesized in the late 1930s. Doctors widely prescribed DES first to pregnant women to prevent miscarriages, and later as an emergency contraceptive pill and to treat breast cancer. However, in 1971, physicians showed a link between DES and vaginal cancer during puberty in the children of women who had taken DES while pregnant. Consequently, the US Food and Drug Administration (FDA) banned its use during pregnancy. In the late 2000s, several studies showed that the grandchildren of women who had consumed DES also suffered medical issues. By the early decades of the twenty-first century, roughly ten million people in the US had been exposed to DES, and three generations of individuals had suffered medical issues due to DES exposure. Researchers class DES as an endocrine disruptor, which affects the form and function of the hormone (endocrine) system.

The Y-chromosome is one of a pair of chromosomes that determine the genetic sex of individuals in mammals, some insects, and some plants. In the nineteenth and twentieth centuries, the development of new microscopic and molecular techniques, including DNA sequencing, enabled scientists to confirm the hypothesis that chromosomes determine the sex of developing organisms. In an adult organism, the genes on the Y-chromosome help produce the male gamete, the sperm cell. Beginning in the 1980s, many studies of human populations used the Y-chromosome gene sequences to trace paternal lineages. In mammals, the Y-chromosomes contain the master-switch gene for sex determination, called the sex-determining region Y, or the SRY gene in humans. In most normal cases, if a fertilized egg cell, called a zygote, has the SRY gene, the zygote develops into an embryos that has male sex traits. If the zygote lacks the SRY gene or if the SRY gene is defective, the zygote develops into an embryo that has female sex traits.

Published in 1971, Adenocarcinoma of the Vagina: Association of Maternal Stilbestrol Therapy with Tumor Appearance in Young Women, by Arthurs L. Herbst and colleagues, was the first piece of literature connecting maternal use of the drug diethylstilbestrol (DES), also called stilbestrol, with the development of a rare and severe form of vaginal cancer in young women. Diethylstilbestrol was later classified as an endocrine disruptor, a substance that disrupts the hormonal function of the body in those exposed to it during development or later in life. After Herbst and his team established the connection between DES and the occurrence of breast cancer, cervical cancer, infertility, and reproductive abnormalities, the US federal government banned use the drug for pregnant women. The article was published in the New England Journal of Medicine.

In 2012, a team of scientists across the US conducted an experiment to find the mechanism that allowed a group of flatworms, planarians, to regenerate any body part. The group included Danielle Wenemoser, Sylvain Lapan, Alex Wilkinson, George Bell, and Peter Reddien. They aimed to identify genes that are expressed by planarians in response to wounds that initiated a regenerative mechanism. The researchers determined several genes as important for tissue regeneration. The investigation helped scientists explain how regeneration is initiated and describe the overall regenerative mechanism of whole organisms.

Diana W. Bianchi studied the medical treatment of premature and newborn infants in the US during the twentieth and twenty-first centuries. Bianchi helped develop non-invasive prenatal genetic tests that use cell-free fetal DNA found within maternal blood to diagnose genetic abnormalities of the fetus during pregnancy. The test provides a means to test fetuses for chromosomal and genetic abnormalities.

Lysogenic bacteria, or virus-infected bacteria, were the primary experimental models used by scientists working in the laboratories of the Pasteur Institute in Paris, France, during the 1950s and 1960s. Historians of science have noted that the use of lysogenic bacteria as a model in microbiological research influenced the scientific achievements of the Pasteur Institute's scientists. Francois Jacob and Jacques Monod used lysogenic bacteria to develop their operon model of gene regulation, to investigate the cellular regulatory mechanisms of the lysogenic life cycle, and to infer the process of cellular differentiation in the development of more complex eukaryotes.