Transcriptome-based molecular staging of human stem cell-derived retinal organoids uncovers accelerated photoreceptor differentiation by 9-cis retinal

Differentiation of neural retina in organoid cultures from human pluripotent stem cells (PSCs) is highly variable and requires an extended period of as many as 200 days. To provide objective assessment of different protocols and culture conditions, we performed transcriptome analysis and molecular staging using RNA-seq data from developing and adult human retina. Using a modified protocol with 9-cis retinal (9CRAL) instead of widely-used all-trans retinoic acid (ATRA) in the culture media, we show comparable differentiation of human embryonic and induced PSCs into a polarized, laminated architecture with all retinal cell types in retinal organoids. Transcriptome comparisons of multiple developing organoids to that of human fetal and adult retina have permitted molecular staging of the differentiation state and uncovered expedited rod photoreceptor maturation by 9CRAL. A direct comparison with the ATRA-organoid cultures revealed higher expression of rhodopsin and other rod genes in 9CRAL-organoids. Our studies thus provide a framework for transcriptome-based staging of retinal organoids to facilitate advances in human disease modeling and evaluation of therapies.