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Germ Layers

A germ layer is a group of cells in an embryo that interact with each other as the embryo develops and contribute to the formation of all organs and tissues. All animals, except perhaps sponges, form two or three germ layers. The germ layers develop early in embryonic life, through the process of gastrulation. During gastrulation, a hollow cluster of cells called a blastula reorganizes into two primary germ layers: an inner layer, called endoderm, and an outer layer, called ectoderm.

Format: Articles

Subject: Theories, Processes

Endoderm

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.

Format: Articles

Subject: Processes

Victor Jollos (1887-1941)

Victor Jollos studied fruit flies and
microorganisms in Europe and the US, and he introduced the concept of
Dauermodifikationen in the early 1900s. The concept of
Dauermodifikationen refers to environmentally-induced traits that are
heritable for only a limited number of generations. Some scientists
interpreted the results of Jollos's work on Paramecium and Drosophila as
evidence for cytoplasmic inheritance. Jollos was forced to emigrate from
Germany to the United States due to anti-semitic government policies in

Format: Articles

Subject: People

Julia Barlow Platt (1857-1935)

Julia Barlow Platt studied neural crests in animal embryos and became involved in politics in the US during the nineteenth and twentieth centuries. She researched how body and head segments formed in chicks (Gallus gallus) and spiny dogfish (Squalus acanthias). Platt observed that in the mudpuppy (Necturus maculosus), the coordinated migration of neural crest cells in the embryo produced parts of the nervous system, bones, and connective tissues in the head.

Format: Articles

Subject: People

"Derivation of Pluripotent Stem Cells from Cultured Human Primordial Germ Cells" (1998), by John Gearhart et al.

In November 1998, two independent reports were published concerning the first isolation of pluripotent human stem cells, one of which was "Derivation of Pluripotent Stem Cells from Cultured Human Primordial Germ Cells." This paper, authored by John D. Gearhart and his research team - Michael J Shamblott, Joyce Axelman, Shunping Wang, Elizabeith M. Bugg, John W. Littlefield, Peter J. Donovan, Paul D. Blumenthal, and George R. Huggins - was published in Proceedings of the National Academy of Science soon after James A.

Format: Articles

Subject: Publications

Julia Barlow Platt's Embryological Observations on Salamanders' Cartilage (1893)

In 1893, Julia Barlow Platt published her research on the origins of cartilage in the developing head of the common mudpuppy (Necturus maculosus) embryo. The mudpuppy is an aquatic salamander commonly used by embryologists because its large embryonic cells and nuclei are easy to see. Platt followed the paths of cells in developing mudpuppy embryos to see how embryonic cells migrated during the formation of the head. With her research, Platt challenged then current theories about germ layers, the types of cells in an early embryo that develop into adult cells.

Format: Articles

Subject: Experiments, Theories, Processes

Alexis Carrel's Immortal Chick Heart Tissue Cultures (1912-1946)

In an effort to develop tissue culture techniques for long-term tissue cultivation, French surgeon and biologist Alexis Carrel, and his associates, produced and maintained a series of chick heart tissue cultures at the Rockefeller Institute in New York City. From 1912 to 1946, this series of chick heart tissue cultures remained alive and dividing. Since the duration of this culture greatly exceeded the normal chick life span, the cells were deemed immortal.

Format: Articles

Subject: Experiments

Jan Evangelista Purkyne (1787-1869)

Jan Evangelista Purkyne, also called Johannes or Johann Evangelist Purkinje, studied cells in the cerebellum, fibers of the heart, subjective visual phenomenon, and germinal vesicle, in eastern Europe during the early nineteenth century. His investigations provided insights into various mechanisms and structures of the human body. Purkyne introduced techniques for decalcification of bones and teeth, embedding of tissue specimens, and eye examinations.

Format: Articles

Subject: People

"Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells" (2007), by Junying Yu et al.

On 2 December 2007, Science published a report on creating human induced pluripotent stem (iPS) cells from human somatic cells: "Induced Pluripotent Stem Cell Lines Derived from Human Somatic Cells." This report came from a team of Madison, Wisconsin scientists: Junying Yu, Maxim A. Vodyanik, Kim Smuga-Otto, Jessica Antosiewicz-Bourget, Jennifer L. Frane, Shulan Tian, Jeff Nie, Gudrun A. Jonsdottir, Victor Ruotti, Ron Stewart, Igor I. Slukvin, and James A. Thomson.

Format: Articles

Subject: Publications

Epithelium

Frederik Ruysch, working in the Netherlands, introduced the term epithelia in the third volume of his Thesaurus Anatomicus in 1703. Ruysch created the term from the Greek epi, which means on top of, and thele, which means nipple, to describe the type of tissue he found when dissecting the lip of a cadaver. In the mid nineteenth century, anatomist Albrecht von Haller adopted the word epithelium, designating Ruysch's original terminology as the plural version. In modern science, epithelium is a type of animal tissue in which cells are packed into neatly arranged sheets.

Format: Articles

Subject: Theories, Processes

"Embryonic Stem Cell Lines Derived from Human Blastocytes" (1998), by James Thomson

After becoming chief pathologist at the University of Wisconsin-Madison Wisconsin Regional Primate Center in 1995, James A. Thomson began his pioneering work in deriving embryonic stem cells from isolated embryos. That same year, Thomson published his first paper, "Isolation of a Primate Embryonic Stem Cell Line," in Proceedings of the National Academy of Sciences of the United States of America, detailing the first derivation of primate embryonic stem cells. In the following years, Thomson and his team of scientists - Joseph Itskovitz-Eldor, Sander S. Shapiro, Michelle A.

Format: Articles

Subject: Experiments, Publications

August Friedrich Leopold Weismann (1834-1914)

August Friedrich Leopold Weismann studied how the traits of organisms developed and evolved in a variety of organisms, mostly insects and aquatic animals, in Germany in the late nineteenth and early twentieth centuries. Weismann proposed the theory of the continuity of germ-plasm, a theory of heredity. Weismann postulated that germ-plasm was the hereditary material in cells, and parents transmitted to their offspring only the germ-plasm present in germ-cells (sperm and egg cells) rather than somatic or body cells.

Format: Articles

Subject: People

Gastrulation in Xenopus

The process of gastrulation allows for the formation of the germ layers in metazoan embryos, and is generally achieved through a series of complex and coordinated cellular movements. The process of gastrulation can be either diploblastic or triploblastic. In diploblastic organisms like cnidaria or ctenophora, only the endoderm and the ectoderm form; in triploblastic organisms (most other complex metazoans), triploblastic gastrulation produces all three germ layers.

Format: Articles

Subject: Processes

Fate Map

Early development occurs in a highly organized and orchestrated manner and has long attracted the interest of developmental biologists and embryologists. Cell lineage, or the study of the developmental differentiation of a blastomere, involves tracing a particular cell (blastomere) forward from its position in one of the three germ layers. Labeling individual cells within their germ layers allows for a pictorial interpretation of gastrulation. This chart or graphical representation detailing the fate of each part of an early embryo is referred to as a fate map.

Format: Articles

Subject: Processes

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

"On the Permanent Life of Tissues outside of the Organism" (1912), by Alexis Carrel

'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.

Format: Articles

Subject: Experiments

Mesoderm

Mesoderm is one of the three germ layers, groups of cells that interact early during the embryonic life of animals and from which organs and tissues form. As organs form, a process called organogenesis, mesoderm interacts with endoderm and ectoderm to give rise to the digestive tract, the heart and skeletal muscles, red blood cells, and the tubules of the kidneys, as well as a type of connective tissue called mesenchyme. All animals that have only one plane of symmetry through the body, called bilateral symmetry, form three germ layers.

Format: Articles

Subject: Processes

Ectoderm

Ectoderm is one of three germ layers--groups of cells that coalesce early during the embryonic life of all animals except maybe sponges, and from which organs and tissues form. As an embryo develops, a single fertilized cell progresses through multiple rounds of cell division. Eventually, the clump of cells goes through a stage called gastrulation, during which the embryo reorganizes itself into the three germ layers: endoderm, ectoderm, and mesoderm. After gastrulation, the embryo goes through a process called neurulation, which starts the development of nervous system.

Format: Articles

Subject: Processes

Neural Crest

Early in the process of development, vertebrate embryos develop a fold on the neural plate where the neural and epidermal ectoderms meet, called the neural crest. The neural crest produces neural crest cells (NCCs), which become multiple different cell types and contribute to tissues and organs as an embryo develops. A few of the organs and tissues include peripheral and enteric (gastrointestinal) neurons and glia, pigment cells, cartilage and bone of the cranium and face, and smooth muscle.

Format: Articles

Subject: Theories

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

Subject: Processes, Theories

Gastrulation in Mus musculus (common house mouse)

As mice embryos develop, they undergo a stage of development called gastrulation. The hallmark of vertebrate gastrulation is the reorganization of the inner cell mass (ICM) into the three germ layers: ectoderm, mesoderm, and endoderm. Mammalian embryogenesis occurs within organisms; therefore, gastrulation was originally described in species with easily observable embryos. For example, the African clawed frog (Xenopus laevis) is the most widely used organism to study gastrulation because the large embryos develop inside a translucent membrane.

Format: Articles

Subject: Processes, Experiments

Nikolai Ivanovic Vavilov (1887-1943)

Nikolai Ivanovich Vavilov proposed theories of plant genetic diversity and participated in the political debate about genetics in Soviet Russia in the early twentieth century. Vavilov collected plant species around the world, building one of the first and most comprehensive seed banks, and he spent much of his life researching plant breeding and genetics. Vavilov also developed a theory of the historical centers of origin of cultivated plants. Vavilov spent most of his scientific career in Russia, although he studied abroad and traveled extensively.

Format: Articles

Subject: People

Neurocristopathies

Neurocristopathies are a class of pathologies in vertebrates,
including humans, that result from abnormal expression, migration,
differentiation, or death of neural crest cells (NCCs) during embryonic development. NCCs are cells
derived from the embryonic cellular structure called the neural crest.
Abnormal NCCs can cause a neurocristopathy by chemically affecting the
development of the non-NCC tissues around them. They can also affect the
development of NCC tissues, causing defective migration or

Format: Articles

Subject: Theories

Wilhelm Johannsen's Genotype-Phenotype Distinction

Wilhelm Johannsen in Denmark first proposed the distinction between genotype and phenotype in the study of heredity in 1909. This distinction is between the hereditary dispositions of organisms (their genotypes) and the ways in which those dispositions manifest themselves in the physical characteristics of those organisms (their phenotypes). This distinction was an outgrowth of Johannsen's experiments concerning heritable variation in plants, and it influenced his pure line theory of heredity.

Format: Articles

Subject: Theories

Endothelium

The endothelium is the layer of cells lining the blood vessels in animals. It weighs more than one kilogram in adult humans, and it covers a surface area of 4000 to 7000 square meters. The endothelium is the cellular interface between the circulating blood and underlying tissue. As the medium between these two sets of tissues, endothelium is part of many normal and disease processes throughout the body.

Format: Articles

Subject: Processes, Theories

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