In the mammalian retina, photoreceptors detect light, transmitting these signals through bipolar neurons to retinal ganglion cells. During retinal development, the transcription factor Otx2 directly activates the transcription factors Prdm1 and Vsx2 through cell type-specific enhancers to promote photoreceptor and bipolar cell fates, respectively. Prdm1 promotes photoreceptor development by repressing Vsx2 transcription, and thus bipolar gene expression, but the role of Vsx2 is less clear. Now, Joe Brzezinski, Noah Goodson and colleagues investigate this regulatory network in vivo using a CRISPR/Cas9 electroporation method. The authors compare the simultaneous deletion of Prdm1 and Vsx1 genes with deletion of their Otx2-driven enhancers. Both pairs of deletions abolish Prdm1 and Vsx1 gene expression, and promote amacrine cell development. However, double deletion of the Prdm1 and Vsx2 genes promotes photoreceptor fates, whereas removal of the two enhancers favours bipolar cell differentiation. Furthermore, bipolar cell fate is determined before Vsx2 enhancer activation, and is not required for the maintenance of bipolar cells. Together, these results indicate that photoreceptors are the default fate for Otx2-expressing progenitors, and that there is an early window during differentiation when Vsx2 can commit cells to a bipolar fate.
Keeping an eye on Otx2 targets
Keeping an eye on Otx2 targets. Development 1 July 2020; 147 (13): e1301. doi:
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