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Organogenesis

From Wikipedia, the free encyclopedia

Organogenesisis the phase ofembryonic developmentthat starts at the end ofgastrulationand continues untilbirth.During organogenesis, the threegerm layersformed from gastrulation (theectoderm,endoderm,andmesoderm) form theinternal organsof the organism.[1]

Theendodermofvertebratesproduces tissue within thelungs,thyroid,andpancreas.Themesodermaids in the production ofcardiac muscle,skeletal muscle,smooth muscle,tissues within thekidneys,andred blood cells.Theectodermproduces tissues within theepidermisand aids in the formation ofneuronswithin the brain, andmelanocytes.

The cells of each of the three germ layers undergodifferentiation,a process where less-specialized cells become more-specialized through the expression of a specific set of genes. Cell differentiation is driven by cell signaling cascades.[2]Differentiation is influenced by extracellular signals such as growth factors that are exchanged to adjacent cells which is calledjuxtracrinesignaling or to neighboring cells over short distances which is calledparacrine signaling.[3]Intracellular signals – a cell signaling itself (autocrine signaling) – also play a role in organ formation. These signaling pathways allow for cell rearrangement and ensure that organs form at specific sites within the organism.[1]The organogenesis process can be studied using embryos and organoids.[4]

Organs produced by the germ layers[edit]

Neural precursor cells fold and elongate to form the neural tube. Mesoderm cells condense to form a rod which will send out signals to redirect the ectoderm cells above. This fold along the neural tube sets up the vertebrate central nervous system.

The endoderm is the inner most germ layer of the embryo which gives rise to gastrointestinal and respiratory organs by forming epithelial linings and organs such as the liver, lungs, and pancreas.[5]The mesoderm or middle germ layer of the embryo will form the blood, heart, kidney, muscles, and connective tissues.[5]The ectoderm or outermost germ layer of the developing embryo forms epidermis, the brain, and the nervous system.[5]

Mechanism of organ formation[edit]

While each germ layer forms specific organs, in the 1820s, embryologistHeinz Christian Panderdiscovered that the germ layers cannot form their respective organs without the cellular interactions from other tissues.[1]In humans, internal organs begin to develop within 3–8 weeks after fertilization. Thegerm layersform organs by three processes: folds, splits, and condensation.[6]Folds form in the germinal sheet of cells and usually form an enclosed tube which you can see in the development of vertebrates neural tube. Splits or pockets may form in the germinal sheet of cells forming vesicles or elongations. The lungs and glands of the organism may develop this way.[6]

A primary step in organogenesis for chordates is the development of thenotochord,which induces the formation of theneural plate,and ultimately theneural tubein vertebrate development. The development of the neural tube will give rise to the brain and spinal cord.[1]Vertebrates develop aneural crestthat differentiates into many structures, including bones, muscles, and components of thecentral nervous system.Differentiation of the ectoderm into the neural crest, neural tube, and surface ectoderm is sometimes referred to as neurulation and the embryo in this phase is the neurula. Thecoelomof the body forms from a split of the mesoderm along thesomite axis[1]

Plant organogenesis[edit]

In plants, organogenesis occurs continuously and only stops when the plant dies. In theshoot,theshoot apical meristemsregularly produce new lateral organs (leavesorflowers) and lateral branches. In theroot,newlateral rootsform from weakly differentiated internal tissue (e.g. thexylem-polepericyclein the model plantArabidopsis thaliana).In vitroand in response to specific cocktails of hormones (mainlyauxinsandcytokinins), most plant tissues can de-differentiate and form a mass of dividingtotipotentstem cells called acallus.Organogenesis can then occur from those cells. The type of organ that is formed depends on the relative concentrations of the hormones in the medium. Plant organogenesis can be induced in tissue culture and used to regenerate plants.[7]

See also[edit]

References[edit]

  1. ^abcdeGilbert, S. F.; Barresi, M. J. F. (2017-05-01). "Developmental Biology, 11Th Edition 2016".American Journal of Medical Genetics Part A.173(5): 1430.doi:10.1002/ajmg.a.38166.ISSN1552-4833.
  2. ^Rankin, Scott (2018)."Timing is everything: Reiterative Wnt, BMP and RA signaling regulate developmental competence during endoderm organogenesis".Developmental Biology.434(1): 121–132.doi:10.1016/j.ydbio.2017.11.018.PMC5785443.PMID29217200– via NCBI.
  3. ^Edlund, Helena (July 2002). "Organogenesis: Pancreatic organogenesis — developmental mechanisms and implications for therapy".Nature Reviews Genetics.3(7): 524–532.doi:10.1038/nrg841.ISSN1471-0064.PMID12094230.S2CID2436869.
  4. ^Ader, Marius; Tanaka, Elly M (2014). "Modeling human development in 3D culture".Current Opinion in Cell Biology.31:23–28.doi:10.1016/j.ceb.2014.06.013.PMID25033469.
  5. ^abcKiecker, Clemens; Bates, Thomas; Bell, Esther (2016-03-01)."Molecular specification of germ layers in vertebrate embryos".Cellular and Molecular Life Sciences.73(5): 923–947.doi:10.1007/s00018-015-2092-y.ISSN1420-682X.PMC4744249.PMID26667903.
  6. ^ab"Animal development – Embryonic induction".Encyclopedia Britannica.Retrieved2018-04-04.
  7. ^"Plant and Soil Sciences eLibrary".passel.unl.edu.Retrieved2018-04-04.

External links[edit]

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