ADULT STEM CELLS OF AQUATIC INVERTEBRATES: A NEW, PROMISING FIELD OF RESEARCH
Pubblicato il: 11.10.2021 13:38
The COST Action 16203 MARISTEM, Stem cells of marine/aquatic invertebrates: from basic research to innovative applications, chaired by prof. Loriano Ballarin, is approaching its end. In four years, the network has compared the behavior of adult stem cells (ASCs) in various aquatic phyla. Indeed, while marine/aquatic invertebrates present the widest biological radiation of multicellular eukaryotes, a careful examination of the metazoan phylogenetic tree reveals that ASCs have been studied in only a limited number of phyla of non-bilaterian and spiralian invertebrates including sponges, cnidarians, platyhelminths, tunicates and echinoderms and few research data are available on their adult stem cells (ASCs). A newly published concept paper in Biological Reviews (doi: 10.1111/brv.1280) by MARISTEM network participants try to fill this gap with a detailed study of the properties of the ASCs of above aquatic invertebrates, as compared to the vertebrate ASCs. The paper evidences how aquatic invertebrate ASCs reveal dramatic disparities from the classical vertebrates ASCs. In vertebrates, ASCs are defined as lineage-restricted cells, limited to tissue or organ-specific activities, that are capable of regulating homeostasis, repair and regeneration of tissues and organs. As far as aquatic invertebrate ASCs are concerned, many of them are pluripotent and even totipotent (they do not follow the germline sequestering model of the vertebrates), exhibit morphologies of highly differentiating cells, may generate the entire repertoire of cell types in adult animals, never reside in stem cell niches and may represent up to 40% of all animal cells. As a conclusion, the authors propose an alternative stemness metaphor to the classical Waddington landscape, termed the ‘wobbling Penrose’ landscape. In this metaphor, totipotent ASCs adopt ascending/descending courses of an ‘Escherian stairwell’, in a lifelong totipotency pathway and 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.