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Mesenchymal stem cell
Mesenchymal stem cells, or MSCs, are multipotent stromal cells that can differentiate into a variety of cell types, including: osteoblasts (bone cells), chondrocytes (cartilage cells), and adipocytes (fat cells).
While the terms Mesenchymal Stem Cell and Marrow Stromal Cell have been used interchangeably, neither term is sufficiently descriptive:
Mesenchyme is embryonic connective tissue that is derived from the mesoderm and that differentiates into hematopoietic and connective tissue, whereas MSCs do not differentiate into hematopoietic cells.
Stromal cells are connective tissue cells that form the supportive structure in which the functional cells of the tissue reside. While this is an accurate description for one function of MSCs, the term fails to convey the relatively recently discovered roles of MSCs in the repair of tissue.
Because the cells, called MSCs by many labs today, can encompass multipotent cells derived from other non-marrow tissues, such as umbilical cord blood, adipose tissue, adult muscle, corneal stroma or the dental pulp of deciduous baby teeth, yet do not have the capacity to reconstitute an entire organ, the term Multipotent Stromal Cell has been proposed as a better replacement.
Neural stem cell
Neural stem cells (NSCs) are self-renewing, multipotent cells that generate the main phenotypes of the nervous system. Stem cells are characterized by their capability to differentiate into multiple cell types via exogenous stimuli from their environment. They undergo asymmetric cell division into two daughter cells, one non-specialized and one specialized. NSCs primarily differentiate into neurons, astrocytes, and oligodendrocytes.
A neuron (/ˈnjʊərɒn/ nyewr-on or /ˈnʊərɒn/ newr-on; also known as a neurone or nerve cell) is an electrically excitable cell that processes and transmits information through electrical and chemical signals. These signals between neurons occur via synapses, specialized connections with other cells. Neurons can connect to each other to form neural networks. Neurons are the core components of the nervous system, which includes the brain, and spinal cord of the central nervous system (CNS), and the ganglia of the peripheral nervous system (PNS). Specialized types of neurons include: sensory neurons which respond to touch, sound, light and all other stimuli affecting the cells of the sensory organs, that then send signals to the spinal cord and brain; motor neurons that receive signals from the brain and spinal cord, to cause muscle contractions, and affect glandular outputs, and interneurons which connect neurons to other neurons within the same region of the brain or spinal cord, in neural networks.
Osteoblast (from the Greek combining forms for "bone", οστό, and βλαστάνω, "germinate"). Osteoblasts are cells with single nuclei that synthesize bone. However, in the process of bone formation, osteoblasts function in groups of connected cells. Individual cells cannot make bone, and the group of organized osteoblasts together with the bone made by a unit of cells is usually called the osteon; the basis of this is discussed in "Organization and ultrastructure of osteoblasts" below.Osteoblasts are specialized, terminally differentiated products of mesenchymal stem cells. They synthesize very dense, crosslinked collagen, and several additional specialized proteins in much smaller quantities, including osteocalcin and osteopontin, which comprise the organic matrix of bone.In organized groups of connected cells, osteoblasts produce a calcium and phosphate-based mineral that is deposited, in a highly regulated manner, into the organic matrix forming a very strong and dense mineralized tissue - the mineralized matrix. This is further discussed in "Mineralization of bone" below. The mineralized skeleton is the main support for the bodies of air breathing vertebrates. It also is an important store of minerals for physiological homeostasis including both acid-base balance and calcium or phosphate maintenance.
An osteoclast (from the Greek words for "bone" (Οστό) and "broken" (κλαστός)) is a type of bone cell that resorbs bone tissue. This function is critical in the maintenance and repair of compact bones in the mammalian skeleton. These bones are stronger than aluminum on a weight basis by being a composite material of approximately equal amounts of hydrated protein and mineral. The osteoclast disassembles this very strong composite at a molecular level by secreting acid and a collagenase. This process is known as bone resorption. Osteoclasts and osteoblasts are instrumental in controlling the amount of bone tissue: osteoblasts form bone, osteoclasts re-absorb bone.
A fibroblast is a type of cell that synthesizes the extracellular matrix and collagen, the structural framework (stroma) for animal tissues, and plays a critical role in wound healing. Fibroblasts are the most common cells of connective tissue in animals.
An osteocyte, a star-shaped cell, is the most commonly found cell in mature bone, and can live as long as the organism itself. Osteocytes have an average half life of 25 years, they do not divide, and they are derived from osteoprogenitors, some of which differentiate into active osteoblasts. Osteoblasts/osteocytes develop in mesenchyme.In mature bone, osteocytes and their processes reside inside spaces called lacunae (Latin for a pit) and canaliculi, respectively. When osteoblasts become trapped in the matrix that they secrete, they become osteocytes. Osteocytes are networked to each other via long cytoplasmic extensions that occupy tiny canals called canaliculi, which are used for exchange of nutrients and waste through gap junctions.Although osteocytes have reduced synthetic activity and (like osteoblasts) are not capable of mitotic division, they are actively involved in the routine turnover of bony matrix, through various mechanosensory mechanisms. They destroy bone through a rapid, transient (relative to osteoclasts) mechanism called osteocytic osteolysis. Hydroxyapatite, calcium carbonate and calcium phosphate is deposited around the cell.
Philadelphia chromosome or Philadelphia translocation is a specific chromosomal abnormality that is associated with chronic myelogenous leukemia (CML). It is the result of a reciprocal translocation between chromosome 9 and 22, and is specifically designated t(9;22)(q34;q11). The presence of this translocation is a highly sensitive test for CML, since 95% of people with CML have this abnormality (the remainder have either a cryptic translocation that is invisible on G-banded chromosome preparations, or a variant translocation involving another chromosome or chromosomes as well as the long arm of chromosomes 9 and 22). However, the presence of the Philadelphia (Ph) chromosome is not sufficiently specific to diagnose CML, since it is also found in acute lymphoblastic leukemia (ALL, 25–30% in adult and 2–10% in pediatric cases) and occasionally in acute myelogenous leukemia (AML).
DNA methylation is a biochemical process whereby a methyl group is added to the cytosine or adenine DNA nucleotides.
DNA methylation may stably alter the expression of genes in cells when cells divide and differentiate from embryonic stem cells into specific tissues. The resulting change is normally permanent and unidirectional, preventing a cell from reverting to a stem cell or becoming a different cell type. DNA methylation is typically removed during zygote formation and re-established through successive cell divisions during development. Some methylation modifications that regulate gene expression are heritable and cause genomic imprinting, and hydroxylation of methyl groups occurs rather than complete removal of methyl groups in zygote.DNA methylation suppresses the expression of endogenous retroviral genes and other harmful stretches of DNA that have entered the host genome. DNA methylation also forms the basis of chromatin structure, which enables a single cell to grow into multiple organs or perform multiple functions. DNA methylation also plays a crucial role in the development of nearly all types of cancer.