Animals have evolved a greater diversity of cell types in a multicellular body (100–150 different cell types), compared
with 10–20 in plants, fungi, and protists.[5] The exact number of cell types is, however, undefined, and the Cell Ontology, as of 2021, lists over 2,300 different cell types.[6]
Multicellular organisms
All higher multicellularorganisms contain cells specialised for different functions. Most distinct cell types arise from a single totipotent cell that differentiates into hundreds of different cell types during the course of development. Differentiation of cells is driven by different environmental cues (such as cell–cell interaction) and intrinsic differences (such as those caused by the uneven distribution of molecules during division). Multicellular organisms are composed of cells that fall into two fundamental types: germ cells and somatic cells. During development, somatic cells will become more specialized and form the three primary germ layers: ectoderm, mesoderm, and endoderm. After formation of the three germ layers, cells will continue to specialize until they reach a terminally differentiated state that is much more resistant to changes in cell type than its progenitors.
The simplest organism considered to have well defined cell types are some volvoceans, such as Volvox carteri, in which each organism is composed of distinct and interdependent cell populations, some somatic and some reproductive.[7]
Conceptual definition
Even though the concept of cell type is widely used, specialists still discuss the exact definition of what constitutes a cell type.[8]
^Usoskin D, Furlan A, Islam S, Abdo H, Lönnerberg P, Lou D, Hjerling-Leffler J, Haeggström J, Kharchenko O, Kharchenko PV, Linnarsson S, Ernfors P (January 2015). "Unbiased classification of sensory neuron types by large-scale single-cell RNA sequencing". Nature Neuroscience. 18 (1): 145–53. doi:10.1038/nn.3881. PMID25420068. S2CID205437148.
^Häring M, Zeisel A, Hochgerner H, Rinwa P, Jakobsson JE, Lönnerberg P, La Manno G, Sharma N, Borgius L, Kiehn O, Lagerström MC, Linnarsson S, Ernfors P (June 2018). "Neuronal atlas of the dorsal horn defines its architecture and links sensory input to transcriptional cell types". Nature Neuroscience. 21 (6): 869–880. doi:10.1038/s41593-018-0141-1. PMID29686262. S2CID5057143.
^Margulis L; Chapman MJ (2009). Kingdoms and Domains: An Illustrated Guide to the Phyla of Life on Earth (4th ed.). Amsterdam: Academic Press/Elsevier. p. 116.
^Osumi-Sutherland, David; Xu, Chuan; Keays, Maria; Kharchenko, Peter V.; Regev, Aviv; Lein, Ed; Teichmann, Sarah A. (2021-06-28). "Cell type ontologies of the Human Cell Atlas". Nature Cell Biology. 23 (11): 1129–1135. arXiv:2106.14443. doi:10.1038/s41556-021-00787-7. PMID34750578. S2CID235658396.
^Gilbert, Scott F. (1997). Developmental biology (5th ed.). Sunderland (Mass.): Sinauer. p. 17. ISBN978-0-87893-244-3.
Arendt D (November 2008). "The evolution of cell types in animals: emerging principles from molecular studies". Nature Reviews. Genetics. 9 (11): 868–82. doi:10.1038/nrg2416. PMID18927580. S2CID28467737.
Media related to Cell types at Wikimedia Commons
