Sphaeroforma arctica

Sphaeroforma arctica, is a unicellular eukaryote with a pivotal position in the tree of life. It was first isolated from the arctic marine amphipod Gammarus setosus.[2][1] Like other Ichthyosporeans such as Creolimax and Abeoforma, Sphaeroforma arctica are spherical cells characterized with their capacity to grow into multi-nucleated coenocytes (multi-nucleates cell). However, a unique feature of S. arctica, is that no obvious budding, hyphal, amoeboid, sporal or flagellated growth stages have been observed in laboratory growth conditions.

Sphaeroforma arctica
Sphaeroforma arctica stained with phalloidin and DAPI
Scientific classification
Class: Ichthyosporea
Genus: Sphaeroforma
Species:
S. arctica
Binomial name
Sphaeroforma arctica
Jøstensen, Sperstad, Johansen & Landfald, 2002[1]

Taxonomy

Sphaeroforma is a member of the Ichthyosporea clade, which is the earliest branching holozoan lineage. It is a key organism to understand the origin of animals.

Sphaeroforma arctica, single cells and colonies

Applications

Indeed, Sphaeroforma arctica grows easily in Marine broth, with the particularity of growing synchronously.[3][4] From a cell with 1 single nucleus (although newborn cells have been shown to contain 2 or even 4 nuclei, too[4]), it can grow to reach a 128 nuclei cell before undergoing cellularization (the process by which the coenocytes split up to give new-born cells). Cellularization involves coordinated inward plasma membrane invaginations dependent on an actomyosin network that leads to the formation of a polarized layer of cells resembling an epithelium. This process is associated with tightly regulated transcriptional activation of genes involved in cell adhesion.[5]

Moreover, it has been recently shown that S. arctica contains miRNA as well as the complex miRNA processing machinery. Taken together, Sphaeroforma arctica is a great model organism from both evolutionary and cell biology perspectives.[6]

References
  1. Jøstensen, Jens-Petter; Sperstad, Sigmund; Johansen, Steinar; Landfald, Bjarne (2002-01-01). "Molecular-phylogenetic, structural and biochemical features of a cold-adapted, marine ichthyosporean near the animal-fungal divergence, described from in vitro cultures". European Journal of Protistology. 38 (2): 93–104. doi:10.1078/0932-4739-00855.
  2. Marshall, Wyth L.; Berbee, Mary L. (March 2013). "Comparative morphology and genealogical delimitation of cryptic species of sympatric isolates of Sphaeroforma (Ichthyosporea, Opisthokonta)". Protist. 164 (2): 287–311. doi:10.1016/j.protis.2012.12.002. ISSN 1618-0941. PMID 23352078.
  3. Suga, Hiroshi; Ruiz-Trillo, Iñaki (2013-05-01). "Development of ichthyosporeans sheds light on the origin of metazoan multicellularity". Developmental Biology. 377 (1): 284–292. doi:10.1016/j.ydbio.2013.01.009. ISSN 0012-1606. PMC 4342548. PMID 23333946.
  4. Ondracka, Andrej; Ruiz-Trillo, Iñaki (2017-09-19). "Decoupling of the nuclear division cycle and cell size control in the coenocytic cycle of the ichthyosporean Sphaeroforma arctica". bioRxiv 10.1101/190900.
  5. Dudin, Omaya; Ondracka, Andrej (24 October 2019). "A unicellular relative of animals generates a layer of polarized cells by actomyosin-dependent cellularization". eLife. 8. doi:10.7554/eLife.49801. PMC 6855841. PMID 31647412.
  6. Brate, Jon; Neumann, Ralf Stefan; Fromm, Bastian; Haraldsen, Arthur Alexander Blorstad; Grini, Paul; Shalchian-Tabrizi, Kamran (2016-10-01). "Pre-metazoan origin of animal miRNAs". bioRxiv 10.1101/076190.
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