The cortical alveolum (pl. cortical alveoli) is a cellular organelle consisting of a vesicle located under the cytoplasmic membrane, to which they give support. They have been defined as membrane sacs that strengthen the cellular cortex through the firm fixation to the underlying membrane and microtubules.[1] They typically form a continuous layer that acts as a flexible film, although they can also constitute a semi-rigid structure or the scales of a theca.[2]

Transmission electron micrograph of a thin section of the surface of the ciliate Paramecium putrinum, showing the alveoli (red arrows) under the cell surface

The cortical alveoli are present in protists of the chromist group Alveolata, whose name references these organelles.[3] Although cortical alveoli are very diverse in shape and function among the different groups of protists, they always share the function of supporting the cytoplasmic membrane. In the case of apicomplexan parasites, they're related to the mobility and facilitate the invasion of host cells, thus they have a considerable importance in medicine. In dinoflagellates the alveoli contain cellulose and compose the scales of their armor. Lastly, in ciliates they are part of the cortical complex that supports the extrusomes, the basal bodies of the cilia and the intricate cortical shell.[4]

The term "corticate" comes from an evolutionary hypothesis about the common origin of kingdoms Plantae and Chromista (united by the clade Corticata or Diaphoretickes), because both kingdoms have cortical alveoli in at least one phylum.[5]

References

  1. ↑ Cavalier-Smith, Thomas (2017). "Kingdom Chromista and its eight phyla: a new synthesis emphasising periplastid protein targeting, cytoskeletal and periplastid evolution, and ancient divergences". Protoplasma. 255 (1): 297–357. doi:10.1007/s00709-017-1147-3. PMC 5756292. PMID 28875267.
  2. ↑ Stelly N, Mauger JP, Claret M, Adoutte A (1991). "Cortical alveoli of Paramecium: a vast submembranous calcium storage compartment" (PDF). The Journal of Cell Biology. 113 (1): 103–112. doi:10.1083/jcb.113.1.103. PMID 1848863. S2CID 2395284.
  3. ↑ Adl, et al. (2012). "The revised classification of eukaryotes". Journal of Eukaryotic Microbiology. 59 (5): 429–514. doi:10.1111/j.1550-7408.2012.00644.x. PMC 3483872. PMID 23020233.
  4. ↑ Gould SB, Tham WH, Cowman AF, McFadden GI, Waller RF (2008). "Alveolins, a new family of cortical proteins that define the protist infrakingdom Alveolata". Molecular Biology and Evolution. 25 (6): 1219–1230. doi:10.1093/molbev/msn070. PMID 18359944.
  5. ↑ Cavalier-Smith, Thomas; Chao, Ema E.; Lewis, Rhodri (December 2015). "Multiple origins of Heliozoa from flagellate ancestors: New cryptist subphylum Corbihelia, superclass Corbistoma, and monophyly of Haptista, Cryptista, Hacrobia and Chromista". Molecular Phylogenetics and Evolution. 93 (1): 331–362. doi:10.1016/j.ympev.2015.07.004. PMID 26234272.
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