Polar filament

The term polar filament may refer to either of two analogous structures used for host invasion by different groups of parasites: Myxozoa (Metazoa)[1] and Microsporidia (Fungi),[2][3] respectively.

In Myxozoa

The polar filament is a structure found in the polar capsule of myxosporean organisms. It is homologous to the "penetrant" structure found in cnidocytes.[1]

The polar filament is coiled along the inner wall of the polar capsule, and is capable of rapid extrusion, during which it everts "inside-out". When everted, it is sticky, and likely serves to hold the spore onto the intestinal wall of the prospective host, and to help separate the valves of the spore.

The polar filament is important in species classification. In some species of Ceratomyxa, the polar filament forms a straight basal section, which the rest of the filament coils around, while in the genus Sphaeromyxa, the filament is folded in a zig-zag arrangement rather than being coiled.

References
  1. Americus, Benjamin; Lotan, Tamar; Bartholomew, Jerri L.; Atkinson, Stephen D. (2020). "A comparison of the structure and function of nematocysts in free-living and parasitic cnidarians (Myxozoa)". International Journal for Parasitology. 50 (10–11): 763–769. doi:10.1016/j.ijpara.2020.04.012. PMID 32707121.
  2. Xu, Yanji; Weiss, Louis M. (2005). "The microsporidian polar tube: A highly specialised invasion organelle". International Journal for Parasitology. 35 (9): 941–953. doi:10.1016/j.ijpara.2005.04.003. PMC 3109658. PMID 16005007.
  3. Frixione, Eugenio; Ruiz, Lourdes; Santillán, Moisés; De Vargas, Lourdes V.; Tejero, José M.; Undeen, Albert H. (1992). "Dynamics of polar filament discharge and sporoplasm expulsion by microsporidian spores". Cytoskeleton. 22 (1): 38–50. doi:10.1002/cm.970220105.
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