Neuroectoderm-derived iris muscle characterization at the single-cell resolution in native human iris and a pluripotent stem cell eye model

How the neuroectoderm-derived eye field breaks symmetry to specify iris muscle is not well understood. Recent studies have begun to transcriptionally characterize mouse iris muscle; however, little is known about the transcriptional foundation of human iris development. Human pluripotent stem cells (hPSCs) enable the study of iris muscle specification. Here we compare iris smooth muscle from native adult iris tissues to evaluate successful specification of iris muscle from hPSC lines. We utilize a previously published eye-like organoid protocol that specified cells of the eye field to also generate iris muscle. We describe a population transcriptionally similar to native iris and describe an iris muscle gene signature. Human iris muscle not only contains pigment, but also expresses pigment synthesis genes and is responsive to acetylcholine. Integration of single-cell RNA-seq datasets confirm the similarity between the iris muscle to the adult iris, establishing the usefulness of the model in studying neuroectoderm-derived iris muscle specification, and related diseases.