Stem Cells: Autonomy Interactors that Emerge as Causal Agents and Legitimate Units of Selection

Concise Review: Transmissible Animal Tumors as Models of the Cancer Stem-Cell Process

“…While some previous mention has been made of these tumors in a stem-cell context, this is limited in nature. Rinkevich [37] discussed CTVT and DFTD cells acting as an independent unit of selection in evolutionary terms, rather than any formal evaluation of any CSC potential. More presciently, Tu [38] did briefly discuss DFTD as a potential CSC, within a larger monograph on CSCs, but no formal evaluation was presented.…”

Pluripotent Gametogenic Stem Cells of Asexually Reproducing Invertebrates

“…Pluri/totipotent gametogenic stem cells are similar to germ and embryonic stem cells; evidence of the evolutionary conserved morphological and functional characteristics of pluripotent stem cells typical also to cells of the germ line have been obtained in representatives of such various metazoan phyla as Porifera, Cnidaria, Plathelminthes, Arthropoda and Chordata (Isaeva et al, 2003(Isaeva et al, , 2008b(Isaeva et al, , 2009Shukalyuk et al, , 2007Shukalyuk et al, , 2011Akhmadieva et al, 2007; Extavour & Akam, 2003;Extavour, 2008;Rinkevich, 2009;Sköld et al, 2009;Funayama et al, 2010). The term somatic embryogenesis (Buss, 1987;Blackstone & Jasker, 2003) clearly shows that stem cells providing for asexual reproduction are considered as somatic cells.…”

“…Stem cells in free-living asexually reproducing invertebrates use the own parental organism as a nutritive medium. Germ and pluripotent stem cells are "privileged", "predatory" cells inclined to "parasitism" as has been displayed for colonial ascidians (Buss, 1999;Pancer et al, 1995;Rinkevich, 2009); these cells can survive starvation through "cannibalism" (Kerszberg & Wolpert, 1998). Sexual reproduction and early stages of embryogenesis are relatively conservative in all the animal kingdom due to the monophyly of metazoans (Sköld et al, 2009).…”

“…According to the generally accepted view, stem cells are cells of embryos or adult organisms capable of self-renewing by mitotic reproduction and differentiation into specialized cell types (Weissman et al, 2001;Cogle et al 2003;Müller, 2006;Lohman 2008;Rinkevich et al, 2009;Sköld et al, 2009;Funayama et al, 2010). Two main types of stem cells should be considered: the cells of the germline and the somatic stem cell lineages (Hogan, 2001;Rinkevich, 2009;Srouji & Extavour, 2011). Germ cells are the only cell type capable of generating a new whole organism in animals; everlasting germline cycle continues from one generation to the next, thus the germline escapes the mortality that all somatic cells of an organism ultimately confront (the common view from Weismann, 1892, to Cinalli et al, 2008.…”

“…Stem cells that have the potential to become both somatic and primary germ cells and are morphologically indistinguishable from the latter were defined as "primary stem cells" (Sköld et al, 2009). In animals with asexual reproduction by somatic embryogenesis, the germ lineage remains non-segregated even in the adult organism, the gametes of which differentiate from stem cells (Blackstone & Jasker, 2003;Rinkevich, 2009;Sköld et al, 2009). Examples of such reserve stem cells, capable of differentiating both into germ and somatic cells, include sponge archaeocytes, cnidarian interstitial cells, planarian neoblasts, and stem cells of colonial ascidians (reviews: Isaeva et al, 2008bIsaeva et al, , 2009Frank et al, 2009;Rinkevich et al, 2009;Sköld et al, 2009;Isaeva, 2010;Srouji, Extavour, 2011).…”