Embryo Project Encyclopedia

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.

All cells that have a nucleus, including plant, animal, fungal cells, and most single-celled protists, also have mitochondria. Mitochondria are particles called organelles found outside the nucleus in a cell's cytoplasm. The main function of mitochondria is to supply energy to the cell, and therefore to the organism. The theory for how mitochondria evolved, proposed by Lynn Margulis in the twentieth century, is that they were once free-living organisms. Around two billion years ago, mitochondria took up residence inside larger cells, in a process called endosymbiosis, becoming functional parts of those cells. Within each mitochondrion is the mitochondrial DNA (mtDNA), which is different from the DNA in the cell's nucleus (nDNA). Organisms inherit their mitochondria only from their mothers via egg cells (oocytes). Mitochondria contribute to the development of oocytes, the release of the oocyte from the ovary (ovulation), the union of oocyte and sperm (fertilization), all stages of embryo formation (embryogenesis), and growth of the embryo after fertilization.

'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.

The p53 protein acts as a pivotal suppressor of inappropriate cell proliferation. By initiating suppressive effects through induction of apoptosis, cell senescence, or transient cell-cycle arrest, p53 plays an important role in cancer suppression, developmental regulation, and aging. Its discovery in 1979 was a product of research into viral etiology and the immunology of cancer. The p53 protein was first identified in a study of the role of viruses in cancer through its ability to form a complex with viral tumor antigens. In the same year, an immunological study of cancer also found p53 due to its immunoreactivity with tumor antisera. Although a series of studies found p53 through various routes, and various researchers called it different names, it was eventually confirmed that they had all encountered the same protein, p53.

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. They found that when those genes were changed or mutated, the mutated genes disrupted the normal development of fruit fly larvae. The researchers called one of the genes hedgehog (abbreviated hh). Nusslein-Volhard, Wieschaus, and Edward B. Lewis, at the California Institute of Technology in Pasadena, California, shared the 1995 Nobel Prize for Physiology or Medicine for their research on how genes control early embryonic development in fruit flies. The hedgehog signaling pathway is conserved across many animal taxa or phyla, from Drosophila to humans. The hedgehog signaling pathway controls several key components of embryonic development, stem-cell maintenance, and it influences the development of some cancers.

Edmund Beecher Wilson experimented with Amphioxus (Branchiostoma) embryos in 1892 to identify what caused their cells to differentiate into new types of cells during the process of development. Wilson shook apart the cells at early stages of embryonic development, and he observed the development of the isolated cells. He observed that in the normal development of Amphioxus, all three main types of symmetry, or cleavage patterns observed in embryos, could be found. Wilson proposed a hypothesis that reformed the Mosaic Theory associated with Wilhelm Roux in Germany. Wilson suggested that cells differentiated into other cells when influenced by physiological (dynamic) changes in the hereditary substance contained in cells, and not because of the qualitative division, or parcelling out, of the substance into daughter cells. Wilson published his results in August 1893.

Charles Robert Cantor helped sequence the human genome, and he developed methods to non-invasively determine the genes in human fetuses. Cantor worked in the US during the twentieth and twenty-first centuries. His early research focused on oligonucleotides, small molecules of DNA or RNA. That research enabled the development of a technique that Cantor subsequently used to describe nucleotide sequences of DNA, a process called sequencing, in humans. Cantor was the principal scientist for the Human Genome Project, for which scientists sequenced the entirety of the human genome in 2003. Afterwards, Cantor became the chief scientific officer for Sequenom Inc., a company that provided non-invasive prenatal genetic testing. Such tests use a pregnant woman's blood to identify genetic mutations in a fetus during the first trimester of pregnancy.

In a series of experiments during mid 1930s, a team of researchers in New York helped establish that bacteria of the species Toxoplasma gondii can infect humans, and in infants can cause toxoplasmosis, a disease that inflames brains, lungs, and hearts, and that can organisms that have it. The team included Abner Wolf, David Cowen, and Beryl Paige. They published the results of their experiment in Human Toxoplasmosis: Occurrence in Infants as an Encephalomyelitis Verification of Transmission to Animals. Toxoplasmosis is an infection that causes inflammations in the brain (encephalitis), heart (myocarditis), and lungs (pneumonitis). The disease is caused in organisms that consume items contaminated by the protozoan parasite Toxoplasma gondii. The bacteria can transfer from pregnant women to their fetuses during pregnancy (congenitally), and it can lead those fetuses to develop physical deformities and mental disabilities. The 1930s experiments established Toxoplasma gondii as a human pathogen and helped increase research into congenital toxoplasmosis, enabling later researchers to develop measures to prevent against the disease in pregnant women.

Ooplasmic transfer, also called cytoplasmic transfer, is an outside the body, in vitro fertilization (IVF) technique. Ooplasmic transfer in humans (Homo sapiens) is similar to in vitro fertilization (IVF), with a few additions. IVF is the process in which doctors manually combine an egg and sperm cells in a laboratory dish, as opposed to artificial insemination, which takes place in the female's body. For ooplasmic transfer, doctors withdraw cytoplasm from a donor's oocyte, and then they inject that cytoplasm with sperm into a patient's oocyte. Doctors perform ooplasmic transfer to replace mitochondria that have genetic defects, which can cause a variety of diseases. In 1982, Audrey Muggleton-Harris's group at MRC Laboratory Animals Center in Surrey, United Kingdom, developed the technique and reported the first successful mammalian ooplasmic transfer in mice (Mus musculus).

In a series of experiments between 1960 and 1965, Robert Geoffrey Edwards discovered how to make mammalian egg cells, or oocytes, mature outside of a female's body. Edwards, working at several research institutions in the UK during this period, studied in vitro fertilization (IVF) methods. He measured the conditions and timings for in vitro (out of the body) maturation of oocytes from diverse mammals including mice, rats, hamsters, pigs, cows, sheep, and rhesus monkeys, as well as humans. By 1965, he manipulated the maturation of mammalian oocytes in vitro, and discovered that the maturation process took about the same amount of time as maturation in the body, called in vivo. The timing of human oocyte maturation in vivo, extrapolated from Edwards's in vitro study, helped researchers calculate the timing for surgical removal of human eggs for IVF.