In the center of the diagram are three of the early steps in the development of a mammal. On the top and bottom are some of the fully-differentiated cell types that will eventually form in the adult.

In developmental biology, cellular differentiation is the process by which a less specialized cell becomes a more specialized cell type. Differentiation occurs numerous times during the development of a multicellular organism as the organism changes from a single zygote to a complex system of tissues and cell types. Differentiation is a common process in adults as well: adult stem cells divide and create fully-differentiated daughter cells during tissue repair and during normal cell turnover. Cell differentiation causes its size, shape, polarity, metabolic activity, and responsiveness to signals to change dramatically. These changes are largely due to highly-controlled modifications in gene expression. With a few exceptions, cellular differentiation almost never involves a change in the DNA sequence itself. Thus, different cells can have very different physical characteristics despite having the same genome. Image File history File links Cell_differentiation. ... Image File history File links Cell_differentiation. ... Views of a Foetus in the Womb, Leonardo da Vinci, ca. ... Drawing of the structure of cork as it appeared under the microscope to Robert Hooke from Micrographia which is the origin of the word cell being used to describe the smallest unit of a living organism Cells in culture, stained for keratin (red) and DNA (green) The cell is the... A cell type is a distinct morphological or functional form of cell. ... Wild-type Caenorhabditis elegans hermaphrodite stained to highlight the nuclei of all cells Multicellular organisms are organisms consisting of more than one cell, and having differentiated cells that perform specialized functions. ... For other meanings see Zygote (disambiguation). ... Biological tissue is a group of cells that perform a similar function. ... Stem cell division and differentiation. ... This does not adequately cite its references or sources. ... Structure of the coenzyme adenosine triphosphate, a central intermediate in energy metabolism. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... The structure of part of a DNA double helix Deoxyribonucleic acid, or DNA, is a nucleic acid molecule that contains the genetic instructions used in the development and functioning of all known living organisms. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ...

A cell that is able to differentiate into many cell types is known as pluripotent. These cells are called stem cells in animals and meristematic cells in higher plants. A cell that is able to differentiate into all cell types is known as totipotent. In mammals, only the zygote and early embryonic cells are totipotent, while in plants, many differentiated cells can become totipotent with simple laboratory techniques. In cytopathology the level of cellular differentiation is used as a measure of cancer progression. "Grade" is a marker of how differentiated a cell in a tumor is. In cell biology, a pluripotent cell is one able to differentiate into many cell types. ... Mouse embryonic stem cells with fluorescent marker. ... Tunica-Corpus model of the apical meristem. ... A cell type is a distinct morphological or functional form of cell. ... Totipotency is the ability of a single cell, usually a stem cell, to divide and produce all the differentiated cells in an organism, including extraembrionic tissues. ... For other uses, see Embryo (disambiguation). ... Totipotency is the ability of a single cell, usually a stem cell, to divide and produce all the differentiated cells in an organism, including extraembrionic tissues. ... Cytopathology is a branch of pathology that studies and diagnoses diseases on the cellular level. ... Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ... In pathology, Grading is a measure of the progress of tumors. ...

Mammalian cell types

Three basic categories of cells make up the mammalian body: germ cells, somatic cells, and stem cells. Each of the approximately 100,000,000,000,000 (10¹⁴) cells in an adult human has its own copy or copies of the genome except certain cell types, such as red blood cells, that lack nuclei in their fully differentiated state. Most cells are diploid; they have two copies of each chromosome. Such cells, called somatic cells, make up most of the human body, such as skin and muscle cells. A germ cell is part of the germline and is involved in the reproduction of organisms. ... This article does not cite any references or sources. ... Mouse embryonic stem cells with fluorescent marker. ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... “Red cell” redirects here. ... Diploid (meaning double in Greek) cells have two copies (homologs) of each chromosome (both sex- and non-sex determining chromosomes), usually one from the mother and one from the father. ... For information about chromosomes in genetic algorithms, see chromosome (genetic algorithm). ...

Germ line cells are any line of cells that give rise to gametes—eggs and sperm—and thus are continuous through the generations. Stem cells, on the other hand, have the ability to divide for indefinite periods and to give rise to specialized cells. They are best described in the context of normal human development. Gametes (in Greek: γαμέτες) —also known as sex cells, germ cells, or spores—are the specialized cells that come together during fertilization (conception) in organisms that reproduce sexually. ...

Development begins when a sperm fertilizes an egg and creates a single cell that has the potential to form an entire organism. In the first hours after fertilization, this cell divides into identical cells. In humans, approximately four days after fertilization and after several cycles of cell division, these cells begin to specialize, forming a hollow sphere of cells, called a blastocyst. The blastocyst has an outer layer of cells, and inside this hollow sphere, there is a cluster of cells called the inner cell mass. The cells of the inner cell mass will go on to form virtually all of the tissues of the human body. Although the cells of the inner cell mass can form virtually every type of cell found in the human body, they cannot form an organism. These cells are referred to as pluripotent. For other uses, see Sperm (disambiguation). ... In most birds and reptiles, an egg (Latin ovum) is the zygote, resulting from fertilization of the ovum. ... The blastocyst is an early stage of the human (or any other mammal) development early in pregnancy. ... The inner cell mass is surrounded by the single cell layer of cells called trophoblast. ... In cell biology, a pluripotent cell is one able to differentiate into many cell types. ...

Pluripotent stem cells undergo further specialization into multipotent progenitor cells that then give rise to functional cells. Examples of stem and progenitor cells include: Multipotent stem cells can give rise to several other cell types, but those types are limited in number. ... The term progenitor cell is used in cell biology and developmental biology to refer to immature or undifferentiated cells, typically found in post-natal animals. ...

• Hematopoietic stem cells (adult stem cells) from the bone marrow that give rise to red blood cells, white blood cells, and platelets
• Mesenchymal stem cells (adult stem cells) from the bone marrow that give rise to stromal cells, fat cells, and types of bone cells
• Epithelial stem cells (progenitor cells) that give rise to the various types of skin cells
• Muscle satellite cells (progenitor cells) that contribute to differentiated muscle tissue

Sketch of bone marrow and its cells Pluripotential hemopoietic stem cells (PHSCs) are stem cells found in the bone marrow. ... For the Dir en grey album, see The Marrow of a Bone. ... “Red cell” redirects here. ... White Blood Cells redirects here. ... A 250 ml bag of newly collected platelets. ... Mesenchymal stem cells or MSCs are multipotent stem cells that can differentiate into a variety of cell types. ... For the Dir en grey album, see The Marrow of a Bone. ... In zootomy, epithelium is a tissue composed of a layer of cells. ... Satellite cells are found in the mature muscle around the muscle fibres, and differentiate from myoblasts. ... For other uses of Muscle, see Muscle (disambiguation). ...

Dedifferentiation

Dedifferentiation is a cellular process often seen in lower life forms such as worms and amphibians in which a partially or terminally differentiated cell reverts to an earlier developmental stage, usually as part of a regenerative process.^{[1] [2]} Dedifferentiation also occurs in plants^[3]. Cells in cell culture can lose properties they originally had, such as protein expression, or change shape. This process is also termed dedifferentiation^[4]. For other uses, see Worm (disambiguation). ... For other uses, see Amphibian (disambiguation). ... In biology, regeneration is an organisms ability to replace body parts. ... Epithelial cells in culture, stained for keratin (red) and DNA (green) Cell culture is the process by which either prokaryotic or eukaryotic cells are grown under controlled conditions. ...

Some believe dedifferentiation is an aberration of the normal development cycle that results in cancer,^[5] whereas others believe it to be a natural part of the immune response lost by humans at some point as a result of evolution. Cancer is a class of diseases or disorders characterized by uncontrolled division of cells and the ability of these to spread, either by direct growth into adjacent tissue through invasion, or by implantation into distant sites by metastasis (where cancer cells are transported through the bloodstream or lymphatic system). ...

A small molecule dubbed reversine, a purine analog, has been discovered that has proven to induce dedifferentiation in myotubes. These dedifferentiated cells were then able to redifferentiate into osteoblasts and adipocytes.^[6] Reversine, or 2-(4-morpholinoanilino)-6-cyclohexylaminopurine, is a small molecule developed by the group of Peter Schultz, used for stem cell dedifferentiation. ... Purine (1) is a heterocyclic aromatic organic compound, consisting of a pyrimidine ring fused to an imidazole ring. ...

Mechanisms

Each specialized cell type in an organism expresses a subset of all the genes that constitute the genome of that species. Each cell type is defined by its particular pattern of regulated gene expression. Cell differentiation is thus a transition of a cell from one cell type to another and it involves a switch from one pattern of gene expression to another. Cellular differentiation during development can be understood as the result of a gene regulatory network. A regulatory gene and its cis-regulatory modules are nodes in a gene regulatory network; they receive input and create output elsewhere in the network ^[7]. The systems biology approach to developmental biology emphasizes the importance of investigating how developmental mechanisms interact to produce predictable patterns (morphogenesis). A cell type is a distinct morphological or functional form of cell. ... Gene expression, or simply expression, is the process by which the inheritable information which comprises a gene, such as the DNA sequence, is made manifest as a physical and biologically functional gene product, such as protein or RNA. Several steps in the gene expression process may be modulated, including the... Superset redirects here. ... For other uses, see Gene (disambiguation). ... In biology the genome of an organism is the whole hereditary information of an organism that is encoded in the DNA (or, for some viruses, RNA). ... For other uses, see Species (disambiguation). ... Gene modulation redirects here. ... A gene regulatory network (also called a GRN or genetic regulatory network) is a collection of DNA segments in a cell which interact with each other (indirectly through their RNA and protein expression products) and with other substances in the cell, thereby governing the rates at which genes in the... Systems biology is a term used very widely in the biosciences, particularly from the year 2000 onwards, and in a variety of contexts. ... Morphogenesis (from the Greek morphê shape and genesis creation) is one of three fundamental aspects of developmental biology along with the control of cell growth and cellular differentiation. ...

A few evolutionarily conserved types of molecular processes are often involved in the cellular mechanisms that control these switches. The major types of molecular processes that control cellular differentiation involve cell signaling. Many of the signal molecules that convey information from cell to cell during the control of cellular differentiation are called growth factors. Although the details of specific signal transduction pathways vary, these pathways often share the following general steps. A ligand produced by one cell binds to a receptor in the extracellular region of another cell, inducing a conformational change in the receptor. The shape of the cytoplasmic domain of the receptor changes, and the receptor acquires enzymatic activity. The receptor then catalyzes reactions that phosphorylate other proteins, activating them. A cascade of phosphorylation reactions eventually activates a dormant transcription factor or cytoskeletal protein, thus contributing to the differentiation process in the target cell ^[8]. Cells and tissues can vary in competence, their ability to respond to external signals ^[9]. This article is about evolution in biology. ... Cell signaling is part of a complex system of communication that governs basic cellular activities and coordinates cell actions. ... Growth factor is a protein that acts as a signaling molecule between cells (like cytokines and hormones) that attaches to specific receptors on the surface of a target cell and promotes differentiation and maturation of these cells. ...

Induction refers to cascades of signaling events, during which a cell or tissue signals to another cell or tissue to influence its developmental fate ^[9]. Yamamoto and Jeffery^[10] investigated the role of the lens in eye formation in cave- and surface-dwelling fish, a striking example of induction^[9]. Through reciprocal transplants, Yamamoto and Jeffery^[10] found that the lens vesicle of surface fish can induce other parts of the eye to develop in cave- and surface-dwelling fish, while the lens vesicle of the cave-dwelling fish cannot^[9]. Look up induction in Wiktionary, the free dictionary. ...

Other important mechanisms fall under the category of asymmetric cell divisions, divisions which give rise to daughter cells with distinct developmental fates. Asymmetric cell divisions can occur because of segregation of cytoplasmic determinants or because of signaling ^[9]. In the former mechanism, distinct daughter cells are created during cytokinesis because of an uneven distribution of regulatory molecules in the parent cell; the distinct cytoplasm that each daughter cell inherits results in a distinct pattern of differentiation for each daughter cell. A well-studied example of pattern formation by asymmetric divisions is body axis patterning in Drosophila. RNA molecules are an important type of intracellular differentiation control signal. The molecular and genetic basis of asymmetric cell divisions has also been studied in green algae of the genus Volvox, a model system for studying how unicellular organisms can evolve into multicellular organisms ^[9]. In Volvox carteri, the 16 cells in the anterior hemisphere of a 32-celled embryo divide asymmetrically, each producing one large and one small daughter cell. The size of the cell at the end of all cell divisions determines whether it will become a specialized germ or somatic cell ^{[9] [11]}. A cell that has almost completed cytokinesis. ... Drosophila has long been a favorite model system for geneticists and developmental biologists studying embroygenesis. ... For other uses, see RNA (disambiguation). ... Species Volvox aureus Volvox carteri () Volvox globator Volvox dissipatrix Volvox tertius Volvox is one of the best-known chlorophytes and is the most developed in a series of genera that form spherical colonies. ...

See also

• Morphogenesis
• Multipotent
• Germ layer
• Cell fate determination

References

• What is a cell? 2004. A Science Primer: A Basic Introduction to the Science Underlying NCBI Resources. NCBI.