![]() ![]() The true innovation in the evolution was the generation of gametogenic germ line, the loss of gametogenic potential from the majority of cells of the organism and protection of the germ line throughout development ( Extavour, 2008 Strouji & 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). 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). However, comparative studies of stem cells in various multicellular organisms are required to understand molecular mechanisms of maintaining pluri/totipotency, “stemness”, which still remain far from clear, as well as mechanisms that regulate gametogenesis, reproduction, development and regeneration.Īccording 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). The study of mammalian embryonic stem cells has become a hot, intensely developing field in biology, biotechnology, and biomedicine. ![]() Stem cells are an essential and defining feature developed during evolution of all multicellular organisms ( Lohman, 2008 Batygina, 2010 Funayama et al., 2010). In this review, morphological and some functional properties of stem cells in different representatives of animals with asexual reproduction (sponges, hydroids, planaria, colonial rhizocephalan crustaceans and colonial ascidia) are considered in comparison with metazoan germline cells and in vitro mammalian embryonic stem cells. ![]()
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