Integrin-alpha-6+ Stem Cells (ISCs) are responsible for whole body regeneration in an invertebrate chordate

Abstract

Colonial ascidians such as Botrylloides are the only chordates able to undergo whole body regeneration (WBR), during which entire new bodies can be regenerated from small fragments of blood vessels. Although it has long been suspected that undifferentiated blood borne cells called hemoblasts play an important role, the cellular and molecular mechanisms of this regeneration process are poorly understood. Here, we show that during the early stages of WBR, proliferation occurs only in small, blood borne cells that express integrin-alpha-6, pou3 and vasa. Proliferating cells can be ablated using Mitomycin C (MMC), leading to loss of WBR. However, regeneration can be rescued by injection of blood cells from a healthy individual into MMC treated vessel fragments. Using FACS-based prospective isolation, we found that injection of a single Integrin-alpha-6 (IA6)-positive cell is capable of rescuing WBR. Lineage tracing using EdU-labeling further revealed that IA6+ cells give rise to regenerating tissues. Our data suggest that ia6+pou3+ cells are proliferating blood borne stem cells that are responsible for whole body regeneration. IA6+ Stem Cells (ISCs) also express notch and frizzled receptors, and inhibitors of either Notch or canonical Wnt signaling block WBR and reduce proliferation, indicating that these two pathways regulate ISC activation.These results provide important insights into the mechanisms and evolution of chordate regeneration.

The eventful history of nonembryonic development in tunicates

“…Despite efforts in the last decade to characterize the cells building vascular buds (Brown, Keeling, Le, & Swalla, 2009;Rinkevich et al, 2010;Sunanaga, Inubushi, & Kawamura, 2010;Sunanaga, Saito, & Kawamura, 2006;Voskoboynik et al, 2007), their nature has remained elusive. Only very recently, Kassmer et al (2019) showed that injection of a single Integrin-alpha6-positive (IA6+) hemoblast in a colony of Botrylloides leachii previously treated with a mitosis inhibitor can rescue budding capacities. The number of IA6+hemoblasts rapidly increases at the onset of vascular budding, participating in the formation of the bud tissues (Kassmer et al, 2019).…”

“…Only very recently, Kassmer et al (2019) showed that injection of a single Integrin-alpha6-positive (IA6+) hemoblast in a colony of Botrylloides leachii previously treated with a mitosis inhibitor can rescue budding capacities. The number of IA6+hemoblasts rapidly increases at the onset of vascular budding, participating in the formation of the bud tissues (Kassmer et al, 2019). Taken together, these results functionally show for the first time the presence of blood-borne multipotent stem cells in Botrylloides leachii.…”

“…Indeed, the nature of these cells may differ from one species to the other. While in Botrylloides leachii they express the stem cell markers Piwi2 and Vasa (Kassmer et al, 2019), Vasa and Piwi1 are not expressed in vascular buds of Botryllus primigenus (Sunanaga et al, 2006(Sunanaga et al, , 2010, while Piwi proteins are only detected in some peripheral cells of vascular bud in Botrylloides violaceus (Brown, Keeling et al, 2009). The third form of NED reported in Stolidobranchia is vasal budding (Figures 1 and 2g), recently described only in Polyandrocarpa zorritensis (Alié et al, 2018;Brunetti & Mastrototaro, 2004;Scelzo et al, 2019).…”

“…While in the last few decades the study of tunicate budding has focused on a few stolidobranch model species (from Sabbadin, 1958 to Kassmer, Langenbacher, & De Tomaso, 2019, reviewed in Manni et al, 2018, much knowledge about the diversity of NED is scattered across almost two centuries of literature. This knowledge has been brilliantly reviewed by others (Berrill, 1951;Brown & Swalla, 2012;Kawamura, Sugino, Sunanaga, & Fujiwara, 2008;Nakauchi, 1982), but an explicit reconstruction of NED history based on a modern understanding of the tunicate phylogeny is still needed.…”

The Diversity of Muscles and Their Regenerative Potential across Animals

“…In the other two ascidian species, Botrylloides leachii and Perophora viridis, a population of adult pluripotent stem cells circulating in the hemolymph seems to be responsible of the regeneration of the whole body, including the entire musculature [ 176 , 177 ]. As for solitary species, the study of these cell populations is still in its infancy.…”