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Bi-directional conversion in Turritopsis nutricula (Hydrozoa)

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... Unlike almost all multicellular animals, including most jellyfish species, some cnidarian species show life cycle reversion, [1][2][3][4][5][6][7][8] in which mature and young medusae transform directly into an earlier developmental stage namely, the polyp stage ( Supplementary Fig. S1). Among such species, Turritopsis dohrnii has been artificially rejuvenated by many means, such as incubation with CsCl and heat shock. ...
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Only two hydromedusan species, Turritopsis dohrnii and T. sp., have exhibited experimental multiple-repeat life cycle reversion in the laboratory, which can be artificially induced by various means such as incubation with CsCl, heat shock, and mechanical damage with needles. In the present study, we constructed a genome assembly of T. dohrnii using Pacific Biosciences long-reads and Illumina short-reads, for which the genome DNA was extracted from 1500 young medusae originated from a single clone. The total length of the draft genome sequence of T. dohrnii was 435.9 Mb (N50 length 747.2 kb). We identified 23,314 high-confidence genes and found the characteristics of RNA expression among developmental stages. Our genome assembly and transcriptome data provide a key model system resource that will be useful for understanding cyclical rejuvenation.
... When exposed to environmental stressors, e.g. starvation, several Cnidarian medusae retain the potential for ontogeny reversal (Bavestrello et al. 1992;Piraino et al. 1996Piraino et al. , 2004De Vito et al. 2006;Schmich et al. 2007;He et al. 2015; due not only to regeneration by proliferation of interstitial cells, but also the occurrence of cell-transdifferentiation processes (Schmid 1974(Schmid , 1992Schmid et al. 1982;Schmid & Alder 1984;Alder & Schmid 1987;Seipel et al. 2004). Transdifferentiation could enable the medusae to evade death and attain potential immortality. ...
... Neoteny is the preservation of juvenile characteristics in adulthood (Bufill et al, 2011). Species displaying neoteny are the Axolotl which remains in its highly regenerative larval stage unless ambient water supply ceases (Safi et al, 2004), the cavedwelling Olm which never leaves its larval stage and is predicted to live > 175 years (Voituron et al, 2011), and "immortal jellyfish" of the genus Turritopsis which can revert from a sexually mature medusa stage into the budding polyp (Bavestrello et al, 1992). Humans are considered to be neotenic apes due to traits such as orthognathy, near absence of body hair, high relative brain weight, and prolonged growth periodNeotenic traits have also been described for NMR including small size, lack of hair, and slow brain maturation reviewed in (Skulachev et al, 2017). ...
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Adult stem cells (ASCs) in vertebrates and model invertebrates (e.g. Drosophila melanogaster) are typically long-lived, lineage-restricted, clonogenic and quiescent cells with somatic descendants and tissue/organ-restricted activities. Such ASCs are mostly rare, morphologically undifferentiated, and undergo asymmetric cell division. Characterized by 'stemness' gene expression, they can regulate tissue/organ homeostasis, repair and regeneration. By contrast, analysis of other animal phyla shows that ASCs emerge at different life stages, present both differentiated and undifferentiated phenotypes, and may possess amoeboid movement. Usually pluri/totipotent, they may express germ-cell markers, but often lack germ-line sequestering, and typically do not reside in discrete niches. ASCs may constitute up to 40% of animal cells, and participate in a range of biological phenomena, from whole-body regeneration, dormancy, and agametic asexual reproduction, to indeterminate growth. They are considered legitimate units of selection. Conceptualizing this divergence, we present an alternative stemness metaphor to the Waddington landscape: the 'wobbling Penrose' landscape. Here, totipotent ASCs adopt ascending/descending courses of an 'Escherian stairwell', in a lifelong totipotency pathway. ASCs may also travel along lower stemness echelons to reach fully differentiated states. However, from any starting state, cells can change their stemness status, underscoring their dynamic cellular potencies. Thus, vertebrate ASCs may reflect just one metazoan ASC archetype.
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