Specialized Cytonemes Induce Self-Organization of Stem Cells
Specialized cytonemes induce self-organization of stem cells Sergi Junyenta, Clare L. Garcina,1, James L. A. Szczerkowskia,1, Tung-Jui Trieua,1, Joshua Reevesa, and Shukry J. Habiba,2 aCentre for Stem Cells and Regenerative Medicine, King’s College London, SE1 9RT London, United Kingdom Edited by Janet Rossant, Hospital for Sick Children, University of Toronto, Toronto, Canada, and approved February 21, 2020 (received for review November 27, 2019) Spatial cellular organization is fundamental for embryogenesis. cell–cell contact (10). In 1999, Ramírez-Weber and Kornberg Remarkably, coculturing embryonic stem cells (ESCs) and tropho- identified cytonemes as signaling filopodia that orient toward blast stem cells (TSCs) recapitulates this process, forming embryo- morphogen-producing cells and specialize in recruiting develop- like structures. However, mechanisms driving ESC–TSC interaction mental signals (11). Others have also identified cytonemes made remain elusive. We describe specialized ESC-generated cytonemes by ligand-producing cells, which extend the ligand toward re- that react to TSC-secreted Wnts. Cytoneme formation and length sponsive cells (12–14). Both cytoneme types limit ligand dispersion are controlled by actin, intracellular calcium stores, and compo- and effectively facilitate ligand delivery to the responding cells. nents of the Wnt pathway. ESC cytonemes select self-renewal– Cytonemes exist in Drosophila tissues and in other organisms, in- promoting Wnts via crosstalk between Wnt receptors, activation cluding Zebrafish (15), vertebrate embryos (16), and cultured of ionotropic glutamate receptors (iGluRs), and localized calcium human cells (17). transients. This crosstalk orchestrates Wnt signaling, ESC polariza- Mechanisms that regulate ESC–TSC communication and their tion, ESC–TSC pairing, and consequently synthetic embryogenesis.
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