R-spondin 2 is required for optic vesicle morphogenesis and neuroretina specification in vivo and in vitro

Using stem cellbased therapies to treat retinal abnormalities is becoming a likely possibility; therefore, identifying the key factors and the relevant mechanisms controlling optic vesicle morphogenesis and neuroretina (NR) differentiation is important. Recent advances in self-organizing, 3-dimensional (3D) tissue cultures of embryonic stem cells (ESCs) and induced pluripotent stem cells (iPSCs) provided a valuable in vitro model for characterizing regulatory cascades and signaling pathways controlling mammalian retinal development. Using Rx-GFP expressing ESCs and Six3/ iPSCs we identified R-spondin 2 (Rspo2)-mediated repression of Wnt signaling as a novel required step during optic vesicle morphogenesis and NR differentiation. Furthermore, we also show that transient ectopic expression of Rspo2 in the anterior neural plate of transgenic mouse embryos was sufficient to arrest NR differentiation. ChIP assays identified Six3-responsive elements in the Rspo2-promoter region, indicating that Six3-mediated repression of Rspo2 is required to restrict Wnt signaling in the developing anterior neuroectoderm and allow eye development to proceed.

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Takata N, Abbey D, Fiore L, Acosta S, Feng R, Gil HJ, Lavado A, Geng X, Interiano A, Neale G, Eiraku M, Sasai Y, Oliver G