Embryo Project Encyclopedia Articles

Endoderm is one of the germ layers-- aggregates of cells that organize early during embryonic life and from which all organs and tissues develop. All animals, with the exception of sponges, form either two or three germ layers through a process known as gastrulation. During gastrulation, a ball of cells transforms into a two-layered embryo made of an inner layer of endoderm and an outer layer of ectoderm. In more complex organisms, like vertebrates, these two primary germ layers interact to give rise to a third germ layer, called mesoderm. Regardless of the presence of two or three layers, endoderm is always the inner-most layer. Endoderm forms the epithelium-- a type of tissue in which the cells are tightly linked together to form sheets-- that lines the primitive gut. From this epithelial lining of the primitive gut, organs like the digestive tract, liver, pancreas, and lungs develop.

The sex of a reptile embryo partly results from the production of sex hormones during development, and one process to produce those hormones depends on the temperature of the embryo's environment. The production of sex hormones can result solely from genetics or from genetics in combination with the influence of environmental factors. In genotypic sex determination, also called genetic or chromosomal sex determination, an organism's genes determine which hormones are produced. Non-genetic sex determination occurs when the sex of an organism can be altered during a sensitive period of development due to external factors such as temperature, humidity, or social interactions. Temperature-dependent sex determination (TSD), where the temperature of the embryo's environment influences its sex development, is a widespread non-genetic process of sex determination among vertebrates, including reptiles. All crocodilians, most turtles, many fish, and some lizards exhibit TSD.

In 2015, biologist Helena D. Zomer and colleagues published the review article “Mesenchymal and Induced Pluripotent Stem Cells: General Insights and Clinical Perspectives” or “Mesenchymal and Induced Pluripotent Stem Cells” in Stem Cells and Cloning: Advances and Applications. The authors reviewed the biology of three types of pluripotent stem cells, embryonic stem cells, or ESCs, mesenchymal stem cells, or MSCs, and induced pluripotent stem cells, or iPS cells. Pluripotent stem cells are a special cell type that can give rise to other types of cells and are essential for development. The authors describe the strengths and weaknesses of each type of stem cell for regenerative medicine applications. They state that both MSC and iPS types of stem cells have the potential to regenerate tissues among many other therapeutic possibilities. In their article, Zomer and colleagues review the potential for MSCs and iPS cells to reshape the field of regenerative and personal medicine.

The goal of this research project was to examine how different messaging techniques, and especially expressions of emotionality surrounding the loss and recovery of biodiversity, can differently influence public attitudes about conservation and the environment. This question was explored using the case of de-extinction, an emerging and controversial conservation technology. De-extinction claims to “resurrect” extinct species, challenging widely held notions of extinction as permanent. Yet seeing extinction as reversible may shift how people feel about biodiversity loss and our moral responsibility to stop it.

Jérôme Lejeune was a French physician and researcher who studied genetics and developmental disorders. According to the Jérôme Lejeune Foundation, in 1958, Lejeune discovered that the existence of an extra twenty-first chromosome, a condition called Trisomy 21, causes Down Syndrome. Down Syndrome is a condition present in an individual since birth and is characterized by physical and developmental anomalies such as small ears, a short neck, heart defects, and short height as children and adults. Throughout his career, Lejeune also discovered that other developmental disorders, such as cri du chat (cry of the cat) syndrome, were caused by chromosomal abnormalities. Lejeune also used his influence in the scientific community to promote pro-life beliefs, and often met with Pope John Paul II to discuss ethical dilemmas such as abortion of fetuses after detection of chromosomal abnormalities. Lejeune was one of the first researchers to link chromosomal abnormalities to developmental disorders with his discovery of Trisomy 21, leading future researchers to identify more links between the two.

George Otto Gey was a scientist in the US who studied cells and cultivated the first continuous human cell line in 1951. Gey derived the cells for that cell line, called the HeLa cell line, from a woman called Henrietta Lacks, a Black woman who had cervical cancer. Cell lines are a cluster of cells that continuously multiply on their own outside of the organism from which they originated. Gey developed new techniques for in vitro, or laboratory-based, maintenance of organs and hormonal tissue, created new methods for cell cultivation, and researched nutritional media, or cell food. Much of his research involved tissue culture, which is the process by which cells are grown under controlled conditions. He also founded what is now known as the Tissue Culture Association, or the TCA, which centered around furthering laboratory research around tissue culturing. By introducing new techniques and methods to cultivate human cells, Gey expanded the laboratory techniques around cell cultivation and helped contribute to a deeper understanding of the human body for future scientific research.

John Langdon Down studied medicine in England in the nineteenth century and was one of the first people to develop a complete description of the disorder that would later be known as Trisomy 21, or Down Syndrome. Down Syndrome is a condition caused by the presence of an extra chromosome, which may cause a person to be born with certain impaired learning abilities and physical features such as a short neck, flattened face, and almond-shaped eyes. In 1866, Down published one of the first accounts to accurately describe people with Down Syndrome, or what he called “Mongolism,” and identify it as a distinct condition. Additionally, Down advocated for people with mental disabilities at a time when their families commonly abandoned them and medical professionals did not prioritize them. He improved the quality of care for people in the centers he worked in and increased their educational opportunities so they would be better prepared to live a normal life. Down brought increased attention to Down Syndrome, leading to the future discovery of the chromosomal anomaly that causes the disorder, and promoting a higher standard of care for people with mental disabilities.

In the United States, most people are assigned both a biological sex and gender at birth based on their chromosomes and reproductive organs. However, there is an important distinction between biological sex and gender. Biological sex, such as male, female, or intersex, commonly refers to physical characteristics. Gender refers to the socially constructed roles, behaviors, and actions people take on, usually in relation to expectations of masculinity or femininity. As of 2022, there is disagreement over the relation between sex and gender. People’s biological sex and gender greatly influence the way they understand themselves, as well as how others treat them and how they interact with society. Moreover, some people’s gender differs from what they were assigned at birth, and they face discrimination, harassment, and violence. Evolving understandings of gender and sex in the US have created more ways for people to live and express their gender identities.

In Australia in the 1940s, Norman McAlister Gregg observed a connection between pregnant women who contracted the rubella virus, or German measles, and cataract formation in their children's eyes. Gregg published his findings in the 1941 article Congenital Cataract following German Measles in the Mother in Transactions of the Ophthalmological Society of Australia. In the article, Gregg analyzed seventy-eight cases of congenital cataracts and suggested that the mothers' environmental factors could cause birth defects, otherwise known as teratogenic effects. Gregg's paper on the teratogenic effects of an environmental agent, the rubella virus, changed the study of birth defects to include viruses as potential causes or teratogens.