Studying Regeneration in Ascidians: An Historical Overview

Abstract

Ascidians are sessile tunicates, that is, marine animals belonging to the phylum Chordata and considered the sister group of vertebrates. They are widespread in all the seas, constituting abundant communities in various ecosystems. Among chordates, only tunicates are able to reproduce asexually, forming colonies. The high regenerative potentialities enabling tunicates to regenerate damaged body parts, or the whole body, represent a peculiarity of this taxon. Here we review the methodological approaches used in more than a century of biological studies to induce regeneration in both solitary and colonial species. For solitary species, we refer to the regeneration of single organs or body parts (e.g., siphon, brain, gonad, tunic, viscera). For colonial species, we review a plethora of experiments regarding the surgical manipulation of colonies, the regeneration of isolated colonial entities, such as single buds in the tunic, or part of tunic and its circulatory system.

New permanent stem cell niche for development and regeneration in a chordate

“…Labelled cells in bud tissues were retrieved in the same locations even when their parent was present, supporting the hypothesis that cells participating in bud development are also stored in the AN. Indeed, the above reported results confirm the presence, in the CCS, of cSCs or progenitor cells contributing to several tissues in bud development, which in turn could explain the massive regenerative abilities found in B. schlosseri and many other colonial ascidians [1][2][3][4][5][24][25][26][27].…”

“…B. schlosseri, as many other colonial tunicate species, show high regenerative capabilities culminating in whole body regeneration [1,2,5,[24][25][26][27][28][29]. This regenerative process happens in the circulatory system, when all the zooids are removed.…”

Regeneration and regengrow in multicellular animals derive from the presence of processes of organ metamorphosis and continuous growth in their life cycles

“…In both larvae and adults, acorn worms can regenerate broad body regions, including the nervous system (Ferrario et al, 2020;Humphreys et al, 2022;Luttrell et al, 2016Luttrell et al, , 2017. Also, among Chordata broad regenerative phenomena are known, especially in Tunicates (Urochordate) but also in Cephalochordates (Ferrario et al, 2020;Holland & Samorjai, 2021;Somorjai, 2017;Somorjai et al, 2012;Vanni et al, 2022). Tunicates can regenerate large body parts and numerous inner organs such as the tunic, viscera, nervous ganglia and even their gonads.…”

“…The regeneration of organs in vertebrates follows the specific evolution that occurred in each class, from their chordate ancestors. The latter were likely capable of broad regeneration, like that of present day tunicates, cephalochordates and in fish larvae and their adults (Holland & Samorjai, 2021; Humphreys et al., 2022; Somorjai, 2017; Vanni et al., 2022). Numerous vertebrates linked to the water environments, such as numerous marine and freshwater fish and amphibians, also show broad regeneration of tissues and of various inner organs, like their marine ancestors.…”