Advances in Aquatic Invertebrate Stem Cell Research

Aquatic invertebrates represent the largest biodiversity and the widest phylogenetic radiation on Earth, with more than 2 million known species. Up until a few years ago, their use as Model organisms in biological research was limited by the paucity of omics data. Recently, the situation has rapidly changed and is still changing. Today, the genomes and various transcriptomes of many aquatic invertebrate species, as well as many recombinant proteins of invertebrate origin, are available. New technologies have revolutionised the available toolbox of research methodologies. This explains the rising interest of researchers in the use of aquatic invertebrates as reliable model organisms. In contrast to the prevalence of diverse oligopotent and unipotent stem cells in vertebrates, aquatic invertebrates (especially non-ecdysozoan invertebrates) exhibit multiple adult cell types with stem cell attributes characterised by multipotency and pluripotency; furthermore, these give rise to cell lineages characteristic of more than a single germ layer, sometimes with somatic and germ line potentials. In addition, unlike vertebrates, aquatic invertebrate adult stem cells are disseminated and widespread inside the animal body, are not associated with a regulatory microenvironment (niche), and do participate in ageing and regeneration phenomena. These properties can help us to better understand the processes and phenomena in mammalian stem cell biology, such as natural chimerism and cancer, ageing and senescence, immunity, and autoimmune responses, which are all difficult to explain or understand in the human context.

Loriano Ballarin (ORCID: 0000-0002-3287-8550) is a Professor of Zoology at the Department of Biology, University of Padova (Italy). He is a member of the editorial board of the Invertebrate Survival Journal and the European Journal of Zoology, and is a founding member of the Italian Association of Developmental and Comparative Immunobiology (IADCI). His main research interests are the evolution of innate immunity and the study of the cellular and molecular basis of immune responses in marine invertebrates, with particular reference to the role of hemocytes/coelomocytes in immune defense and, more generally, in the stress response. Most of his studies were carried out using the colonial ascidian Botryllus schlosseri as a model organism. His interest in stem cells is directly related to their role in hematopoiesis, as they assure the continuous renewal of the circulating immunocytes of marine invertebrates. He is the chair of the COST Action 16203 MARISTEM “Stem cells of marine/aquatic invertebrates: from basic research to innovative applications” that supported the publication of this book. He is author or co-author of more than 130 peer-reviewed publications in scientific journals, co-editor of scientific books, including “Lessons in immunity: from single-cell organisms to mammals” (Elsevier, 2016), and guest editor of Special Issues, including: “Ancient immunity. phylogenetic emergence of recognition-defence mechanisms” (Biology (Basel), 2020–2021).

Baruch (Buki) Rinkevich has been a professor and senior scientist at the National Institute of Oceanography, Haifa, since 1988, the University of Haifa, Israel, since 2008, and an adjunct professor at the Biology Department, Ben-Gurion University in Beer-Sheva, Israel, since 2006. He received his PhD at Tel Aviv University, Israel, on coral physiology, and spent two postdoctoral periods in the United States: at Scripps Oceanographic Institute, La Jolla, California, studying silicification in marine invertebrates, and at Stanford University Medical School California, studying ascidian immunity. A marine biologist, he works on the immunity, allorecognition, and developmental biology of marine invertebrates (primarily corals and colonial tunicates); on cell cultures/stem cell biology of marine invertebrates; on pattern formation of colonial organisms; on the unit of selection; and on coral reef restoration. Other aspects studied by Rinkevich in the laboratory include marine genotoxicity, DNA barcoding, the eDNA of marine organisms, and studies on thraustochytrids. He was the head of the MINERVA Center on “Invertebrate immunology and developmental biology” (1995–2002) and the head of the Department of Marine Biology and Biotechnology, National Institute of Oceanography (2002–2008). He has served on the editorial boards of 18 scientific, peer-reviewed journals, has been the mentor of > 60 graduate students (already graduated and in process), and is the author of > 360 publications and three edited books.

Bert Hobmayer is a Professor of Zoology at the University of Innsbruck, Austria (since 2009). He received his doctoral degree (Dr. rer. nat.) at the University of Munich, Germany, working on mechanisms of regeneration and neurogenesis in the freshwater polyp Hydra. After spending two post-doctorate years at the National Institute of Genetics in Mishima, Japan (characterization of cell-cell adhesion proteins in Hydra), he continued as a zoologist and developmental biologist to study cellular and molecular mechanisms underlying regeneration, axial patterning, and adult stem cell behavior in simple animal models at the Universities of Frankfurt, Darmstadt, and Innsbruck. Focus areas of his research include the roles of Wnt signaling pathways in providing positional information and in orchestrating tissue morphogenesis, and the impact of Myc transcription factors on adult stem cell decision making. At the University of Innsbruck, he served as head of the Department of Zoology (2006–2013) and head of the Special Research Cluster Center for Molecular Biosciences Innsbruck (CMBI) (2016–2021). He also served as a member of the Austrian Ministry of Science Panel “Future Life Sciences” in 2016 and 2017. He mentored more than 20 graduate students and is the author of more than 50 publications, many of which were published in high-impact journals.