NRL-/- gene edited human embryonic stem cells generate rod-deficient retinal organoids enriched in S-cone-like photoreceptors.

Elisa Cuevas, Daniel L Holder, Ashwak H Alshehri, Julie Tréguier, Jörn Lakowski, Jane C Sowden

Stem cells (Dayton, Ohio) 2021 Apr

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Organoid cultures represent a unique tool to investigate the developmental complexity of tissues like the human retina. NRL is a transcription factor required for the specification and homeostasis of mammalian rod photoreceptors. In Nrl-deficient mice, photoreceptor precursor cells do not differentiate into rods, and instead follow a default photoreceptor specification pathway to generate S-cone-like cells. To investigate whether this genetic switch mechanism is conserved in humans, we used CRISPR/Cas9 gene editing to engineer an NRL-deficient embryonic stem cell (ESC) line (NRL-/- ), and differentiated it into retinal organoids. Retinal organoids self-organize and resemble embryonic optic vesicles (OVs) that recapitulate the natural histogenesis of rods and cone photoreceptors. NRL-/- OVs develop comparably to controls, and exhibit a laminated, organized retinal structure with markers of photoreceptor synaptogenesis. Using immunohistochemistry and quantitative polymerase chain reaction (qPCR), we observed that NRL-/- OVs do not express NRL, or other rod photoreceptor markers directly or indirectly regulated by NRL. On the contrary, they show an abnormal number of photoreceptors positive for S-OPSIN, which define a primordial subtype of cone, and overexpress other cone genes indicating a conserved molecular switch in mammals. This study represents the first evidence in a human in vitro ESC-derived organoid system that NRL is required to define rod identity, and that in its absence S-cone-like cells develop as the default photoreceptor cell type. It shows how gene edited retinal organoids provide a useful system to investigate human photoreceptor specification, relevant for efforts to generate cells for transplantation in retinal degenerative diseases. ©2021 The Authors. Stem Cells published by Wiley Periodicals LLC on behalf of AlphaMed Press 2021.

Citation

Elisa Cuevas, Daniel L Holder, Ashwak H Alshehri, Julie Tréguier, Jörn Lakowski, Jane C Sowden. NRL-/- gene edited human embryonic stem cells generate rod-deficient retinal organoids enriched in S-cone-like photoreceptors. Stem cells (Dayton, Ohio). 2021 Apr;39(4):414-428