Stem Cells in Marine Organisms
Do real stem cells and stem cell lineages exist in lower organisms? Can stem cells from one organism parasitize the soma and/or the germ line of conspecifics? Can differentiated cells in marine organisms be re-programmed to regenerate tissues, organs and
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Stem Cells in Asexual Reproduction of Marine Invertebrates Helen Nilsson Sköld, Matthias Obst, Mattias Sköld, and Bertil Åkesson
Abstract While sexual reproduction is conserved and almost ubiquitous, asexual reproduction in forms of parthenogenesis or agametic cloning from somatic tissue is less conserved. The phylogeny shows that agametic cloning is widespread but scattered with many different modes for asexual formation of a new animal. This suggests that independent forms of cloning have evolved later from sexual ancestors between and within different phyla. Here, we present an overview of agametic cloning in the marine animal kingdom and discuss molecular and evolutionary aspects of somatic stem cell usage for asexual cloning. The molecular tissue characterizations and the relative role of different stem cells involved in agametic cloning are only at its beginning with whole phyla largely uncovered. An emerging hypothesis is that the first somatic stem cells used in cloning were also able to form a germ-line and that the more limited lineage specific stem cells are derived. We discuss advantages and problems with agametic cloning from somatic tissue and propose that the levels of stem cell potential held in the tissue can have large consequences for the reproductive life cycle strategies and long-term fitness in clonal animals and strains. We finally describe suitable molecular experimental approaches for future research on this topic. Keywords Agametic cloning · Asexual · Stem cells · Tissue plasticity · Self renewal · Marine invertebrates · Phylogeny · Colonial · Ageing
5.1 Introduction If there were no regeneration there would be no life. If everything regenerated there would be no death. All organisms exist between these two extremes. Richard Goss (1969)
Life is ensured by solutions for individual longevity and by the generation of new individuals. New individuals can be generated sexually by combining genotypes or H.N. Sköld (B) Marine Ecology, Göteborg University, Kristineberg 566, SE 450 34, Fiskebäckskil, Sweden e-mail: [email protected]
B. Rinkevich, V. Matranga (eds.), Stem Cells in Marine Organisms, C Springer Science+Business Media B.V. 2009 DOI 10.1007/978-90-481-2767-2_5,
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asexually from a single parent. Asexual reproduction can be divided into two fundamentally different processes. First, embryos may be generated by parthenogenesis from oocytes, and second the young or adult body may divide or bud as it grows which is defined as agametic cloning. The fundamental difference between these processes lay in the type of cells contributing to the new animal. While sexually formed embryos derive from heavily selected gametes and gamete fusion processes, agametic progeny form from somatic tissue that may be at a different level of cellular differentiation and physiological age than the pluripotent egg or zygote. Many organisms use both sexual and asexual reproduction in their life cycles. While sexual reproduction is conserved and almost ubiquitous in nature an
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