A c-opsin functions in a ciliary-marginal zone-like stem cell region of an invertebrate camera-type eye

Camera-type eyes in vertebrates and invertebrates are striking examples of parallel evolution of a complex structure. Comparisons between such structures can help to deduce their organizational principles. We analyzed the camera-type adult eyes of the bristleworm Platynereis dumerilii . Employing single-cell RNA sequencing, we identified neurogenic cells in the worms’ adult brains. Among those are distinct neural stem cells in its adult eye, adjacent to the glass body/lens, that produce cells in radial lines, reminiscent of stem cells in the vertebrate eye ciliary marginal zone. A subset of these proliferating cells expresses the photoreceptor gene c-opsin1 . c-opsin1 knock-out reduces eye cell proliferation and influences differentiation. During reproductive maturation, proliferation in eye and brain sharply declines, while cells upregulate molecular characteristics of mammalian adult neural stem cell quiescence. Our data reveal new insights into nervous system functional development and evolution.