Stem Cells' Exodus: A Journey to Immortality
ABSTRACT Stem cell niches provide a regulatory microenvironment that retains stem cells and promotes self-renewal. Recently in Developmental Cell, Rinkevich et al. (2013) showed that cell islands (CIs) of Botryllus schlosseri, a colonial chordate, provide niches for maintaining cycling stem cells that migrate from degenerated CIs to newly formed buds.
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ABSTRACT: The mechanisms that sustain stem cells are fundamental to tissue maintenance. Here, we identify "cell islands" (CIs) as a niche for putative germ and somatic stem cells in Botryllus schlosseri, a colonial chordate that undergoes weekly cycles of death and regeneration. Cells within CIs express markers associated with germ and somatic stem cells and gene products that implicate CIs as signaling centers for stem cells. Transplantation of CIs induced long-term germline and somatic chimerism, demonstrating self-renewal and pluripotency of CI cells. Cell labeling and in vivo time-lapse imaging of CI cells reveal waves of migrations from degrading CIs into developing buds, contributing to soma and germline development. Knockdown of cadherin, which is highly expressed within CIs, elicited the migration of CI cells to circulation. Piwi knockdown resulted in regeneration arrest. We suggest that repeated trafficking of stem cells allows them to escape constraints imposed by the niche, enabling self-preservation throughout life.Developmental Cell 12/2012; 24(1). DOI:10.1016/j.devcel.2012.11.010
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ABSTRACT: Evidence from many systems has shown that stem cells are maintained in "niches" or specific regulatory microenvironments formed by stromal cells. The question of how stem cells are maintained in their niches is important, and further studies will lead to a better understanding of stem cell regulation and enhance the future use of stem cells in regenerative medicine. Here we show that cadherin-mediated cell adhesion is required for anchoring somatic stem cells (SSCs) to their niches in the Drosophila ovary. DE-cadherin and Armadillo/beta-catenin accumulate in the junctions between SSCs and their neighboring cells, inner germarial sheath cells. Removal of DE-cadherin from SSCs results in stem cell loss in the adult ovary. Furthermore, the cadherin-mediated adhesion is also important for maintaining SSCs in their niches before adulthood. This study provides further support that SSCs are located in a niche formed by their neighboring cells. We have previously shown that DE-cadherin-mediated cell adhesion is essential for anchoring germ-line stem cells to their niches in the Drosophila ovary. This study further implicates cadherin-mediated cell adhesion as a general mechanism for anchoring stem cells to their niches in a variety of systems.Proceedings of the National Academy of Sciences 12/2002; 99(23):14813-8. DOI:10.1073/pnas.232389399
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ABSTRACT: The topipotency of the germline is the full manifestation of the pluri- and multipotency of embryonic and adult stem cells, thus the germline and stem cells must share common mechanisms that guarantee their multipotentials in development. One of the few such known shared mechanisms is represented by Piwi proteins, which constitute one of the two subfamilies of the Argonaute protein family. Piwi proteins bind to Piwi-interacting RNAs (piRNAs) that are generally 26 to 31 nucleotides in length. Both Piwi proteins and piRNAs are most abundantly expressed in the germline. Moreover, Piwi proteins are expressed broadly in certain types of somatic stem/progenitor cells and other somatic cells across animal phylogeny. Recent studies indicate that the Piwi-piRNA pathway mediates epigenetic programming and posttranscriptional regulation, which may be responsible for its function in germline specification, gametogenesis, stem cell maintenance, transposon silencing, and genome integrity in diverse organisms.Annual Review of Genetics 11/2010; 45(1):447-69. DOI:10.1146/annurev-genet-110410-132541