Biology:Schmidtea mediterranea

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Short description: Species of worm

Schmidtea mediterranea
Scientific classification edit
Kingdom: Animalia
Phylum: Platyhelminthes
Order: Tricladida
Family: Dugesiidae
Genus: Schmidtea
Species:
S. mediterranea
Binomial name
Schmidtea mediterranea
Benazzi, Baguñà, Ballester, Puccinelli & Del Papa, 1975
Distribution of S. mediterranea
(Western Mediterranean)[1]
Synonyms
  • Dugesia mediterranea
    Benazzi, Baguñà, Ballester, Puccinelli & Del Papa, 1975

Schmidtea mediterranea is a freshwater triclad (planarian) that lives in southern Europe and Tunisia.[2] It is a model for regeneration, stem cells and development of tissues such as the brain and germline.[3][4] It is known to be "highly regenerative" with the whole body being regeneratable.[5]

Distribution

Schmidtea mediterranea is found in some coastal areas and islands in the western Mediterranean (Catalonia, Menorca, Mallorca, Corsica, Sardinia, Sicily and Tunisia).[2][6][7][8][9]

Ecology

High water temperatures of 25–27 °C have deleterious effects on populations of S. mediterranea, while this species tolerates variations in the acidity of the water (pH 6.9–8.9) without a noticeable influence on their survival.[2]

S. mediterranea can be found with associated fauna such as gastropods, bivalves, insects, leeches, and nematodes.[2]

Reproduction

The sexual specimens of Schmidtea mediterranea produce cocoons between November and April. In May, when water temperature rises above 20 °C, they lose their reproductive apparatus. Despite this, they don't reproduce asexually (by fissiparity) during the summer months.[2]

Regeneration

Almost any piece from a Schmidtea mediterranea individual can regenerate an entire organism in a few days.[6] This is in part enabled by the presence of abundant adult pluripotent stem cells[10] called neoblasts. Transplantation of a single neoblast to a fatally injured animal has been shown to rescue the animal.[10] Stem cells are intercalated between gut branches. Their niche lies between the intestine and the surface epithilium.[5]

During regeneration, stem cells appear in proximity to mmp-1+ secretory hecatonoblasts and porcupine+ intestinal cells. The hecatonoblasts are dispensable while the intestinal cells are required. Unusually, the intestinal cells do not tend to be in direct contact with the stem cells that they control (or have any cell-cell junctions), a control scheme unusual among invertebrate stem cells.[5]

Genome

A long-read genome of S. mediterranea was sequenced in 2018. Despite the 17 rounds of inbreeding, the resulting genome remained highly heterozygous, suggesting that meiotic recombination is inefficient in this species. The genome has a repetitive fraction of 61.7%. Planarian genomes in general have been difficult to assemble from short-read sequencing due to the heterozygousity, high AT content, resistance to standard DNA isolation procedures, and repeat content. There are a few previously unknown family of long terminal repeats that the author named SLF (S. mediterranea LTR family) followed by a number.[11]

Like other flatwormss, S. mediterranea shows the loss of many genes that are essential to humans and mice. As with all sequenced flatworms (as of 2018), it has no recognizable form of the fatty acid synthase FASN gene, which is essential for de novo fatty acid synthesis in eukaryotes. The heme breakdown genes HMOX1 and BLVRB are missing in this worm while the heme biosynthesis pathway is known to be present from in vivo experiments. The double-strand break repair pathway is mssing many parts, which on one hand makes sense given the structural divergence and repeat content of the genome, but on the other hand is unusual given the worm's resistance to γ-radiation.[11]

Also unusual is the lack of identifiable MAD1 and MAD2 genes, thought to be essential components of the spindle assembly checkpoint (SAC). However, an SAC-like function is known to occur in planarians, as Dugesia dorotocephala displays M-phase arrest upon colchicine interference of spindle function. Additional work shows that the APC/C-CDC20 remains in control of cell cycle and RZZ complex remains in control of APC/C-CDC20 despite the absence of MAD1/2.[11]

References

  1. ↑ E.M. Lazaro, A.H. Harrath, G.A. Stocchino, M. Pala, J. Baguna, M. Riutort, Schmidtea mediterranea phylogeography: an old species surviving on a few Mediterranean islands?, BMC Evolutionary Biology. 11 (2011) 274.
  2. ↑ 2.0 2.1 2.2 2.3 2.4 Abdel Halim Harrath; Mohamed Charni; Ronald Sluys; Fathia Zghal; Saida Tekaya (2004). "Ecology and distribution of the freshwater planarian Schmidtea mediterranea in Tunisia". Italian Journal of Zoology 71 (3): 233–236. doi:10.1080/11250000409356577. 
  3. ↑ Salo E, Baguñà J: Regeneration in planarians and other worms: New findings, new tools, and new perspectives. Journal of Experimental Zoology 2002, 292(6):528-539.
  4. ↑ Reddien PW, Sanchez-Alvarado A: Fundamentals of planarian regeneration. Annu Rev Cell Dev Biol 2004, 20:725-757.
  5. ↑ 5.0 5.1 5.2 Mann, Frederick G.; Brewster, Carolyn E.; Vuu, Dung M.; Mir, Mol; Galton, Riley; Nien, Shao-Fu; Dewars, Enya R.; Guerrero-Hernández, Carlos et al. (October 2025). "Molecular and cellular characterization of planarian stem cell microenvironments". Cell Reports 44 (10). doi:10.1016/j.celrep.2025.116401. 
  6. ↑ 6.0 6.1 Benazzi M, Baguñà J, Ballester R, Puccinelli I, Papa RD: Further Contribution to the Taxonomy of the Dugesia lugubris-polychroa Group with Description of Dugesia mediterranea n. sp. (Tricladida, Paludicola). Bolletino di zoologia 1975, 42(1):81-89.
  7. ↑ Ribas M: Cariologia, sistematica i biogeografia de les Planaries d'aigues dolces al Països Catalans. 1990.
  8. ↑ Baguñà J. Carranza S, Pala M, Ribera C, Giribet G, Arnedo M, Ribas M, Riutort M: From morphology and kariology to molecules. New methods for taxonomical identification of asexual populations of freshwater planarians. A tribute to Professor Mario Benazzi. Italian Journal of Zoology 1999, 66:207-214.
  9. ↑ De Vries EJ, Baguñà J, Ball IR: Chromosomal polymorphism in planarians and the plate tectonics of the western Mediterranean. Genetica 1984, 62:187-191.
  10. ↑ 10.0 10.1 Wagner, Daniel E.; Wang, Irving E.; Reddien, Peter W. (2011-05-13). "Clonogenic Neoblasts Are Pluripotent Adult Stem Cells That Underlie Planarian Regeneration" (in en). Science 332 (6031): 811–816. doi:10.1126/science.1203983. ISSN 0036-8075. PMID 21566185. 
  11. ↑ 11.0 11.1 11.2 Grohme, M. A.; Schloissnig, S.; Rozanski, A.; Pippel, M.; Young, G. R.; Winkler, S.; Brandl, H.; Henry, I. et al. (2018). "The genome of Schmidtea mediterranea and the evolution of core cellular mechanisms". Nature 554 (7690): 56–61. doi:10.1038/nature25473. PMID 29364871. 

Wikidata ☰ Q2158498 entry



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