Fig. 3

Generation of cone photoreceptors in larval and adult fish.

A) Top: developmental time is indicated from right to left. Neuroepithelial progenitor cells in the retinal germinal zone proliferate, exit the cell cycle, and differentiate into cone photoreceptors, Müller glia (shaded grey), and retinal neurons (not shown). Rod photoreceptors are later added to the differentiated retina (left). The apical epithelial surface of the retina (cyan line) is the outer limiting membrane (OLM), as defined by the zonula adherens (ZA). The junctional protein Zonula Occludens (ZO-1) localizes to the OLM. The subapical region (SAR) of the plasma membrane shown in red is in the inner segment of the photoreceptors and is the site of localization of the Crumbs complex. The outer segments of photoreceptors contain the rod and cone opsins and are colored to represent the wavelength absorption maxima of their respective visual pigments. Bottom: the dotted rectangle indicates the retinal margin region illustrated in panels B and D, which straddles the proliferative germinal zone and the adjacent zone of differentiating cones. B) Larval retinal margin with cell boundaries at the level of the zonula adherens indicated by ZO-1 immunostaining, showing the packing of cone cells added through growth at the margin during the larval stage. The germinal zone is at the right. C) The Q₄ orientational order parameter from the image in panel B is plotted as a function of distance from the proliferating germinal zone (at ~15 μm). D) Adult retinal margin; note that straight vertical columns of cones appear abruptly at the edge of the germinal zone and represent a cohort of cells generated approximately synchronously from the germinal zone at the right. The polygonal profiles marked by white stars represent profiles of Müller glia (see Fig. S1J, L). E) The Q₄ orientational order parameter from the image in panel C; note that the value of Q₄ increases sharply at the edge of the germinal zone (at ~15 μm) in the adult retina.