Editing Developmental biology (section)

=== Cell differentiation ===

[[File:Slack Essential Dev Biol Fig 14.12a.jpg|thumb|The Notch-delta system in neurogenesis (Slack Essential Dev Biol Fig 14.12a)]]

[[Cell differentiation]] is the process whereby different functional cell types arise in development. For example, neurons, muscle fibers and hepatocytes (liver cells) are well known types of differentiated cells. Differentiated cells usually produce large amounts of a few proteins that are required for their specific function and this gives them the characteristic appearance that enables them to be recognized under the light microscope. The genes encoding these proteins are highly active. Typically their [[chromatin]] structure is very open, allowing access for the transcription enzymes, and specific transcription factors bind to regulatory sequences in the DNA in order to activate gene expression.<ref>{{cite journal | vauthors = Li B, Carey M, Workman JL | title = The role of chromatin during transcription | journal = Cell | volume = 128 | issue = 4 | pages = 707–19 | date = February 2007 | pmid = 17320508 | doi = 10.1016/j.cell.2007.01.015 | doi-access = free }}</ref><ref>{{cite journal | vauthors = Heintzman ND, Stuart RK, Hon G, Fu Y, Ching CW, Hawkins RD, Barrera LO, Van Calcar S, Qu C, Ching KA, Wang W, Weng Z, Green RD, Crawford GE, Ren B | display-authors = 6 | title = Distinct and predictive chromatin signatures of transcriptional promoters and enhancers in the human genome | journal = Nature Genetics | volume = 39 | issue = 3 | pages = 311–8 | date = March 2007 | pmid = 17277777 | doi = 10.1038/ng1966 | s2cid = 1595885 }}</ref> For example, [[NeuroD]] is a key transcription factor for neuronal differentiation, [[myogenin]] for muscle differentiation, and [[HNF4]] for hepatocyte differentiation.
Cell differentiation is usually the final stage of development, preceded by several states of commitment which are not visibly differentiated. A single tissue, formed from a single type of progenitor cell or stem cell, often consists of several differentiated cell types. Control of their formation involves a process of lateral inhibition,<ref>{{cite journal | vauthors = Meinhardt H, Gierer A | year = 2000 | title = Pattern formation by local self-activation and lateral inhibition | url = http://www.me.ucsb.edu/~moehlis/APC514/2002_1.pdf | journal = BioEssays | volume = 22 | issue = 8| pages = 753–760 | doi = 10.1002/1521-1878(200008)22:8<753::aid-bies9>3.0.co;2-z | pmid = 10918306 | url-status = live | archive-url = https://web.archive.org/web/20171027025156/https://me.ucsb.edu/~moehlis/APC514/2002_1.pdf | archive-date = 2017-10-27 | citeseerx = 10.1.1.477.439 }}</ref> based on the properties of the [[Notch signaling pathway]].<ref>{{cite journal | vauthors = Sprinzak D, Lakhanpal A, Lebon L, Santat LA, Fontes ME, Anderson GA, Garcia-Ojalvo J, Elowitz MB | display-authors = 6 | title = Cis-interactions between Notch and Delta generate mutually exclusive signalling states | journal = Nature | volume = 465 | issue = 7294 | pages = 86–90 | date = May 2010 | pmid = 20418862 | pmc = 2886601 | doi = 10.1038/nature08959 | bibcode = 2010Natur.465...86S }}</ref> For example, in the neural plate of the embryo this system operates to generate a population of neuronal precursor cells in which NeuroD is highly expressed.