Fig. 1
From: Single cones give rise to multi-cone types in the retinas of fishes
Retinal morphology and cone patterning during early photoreceptor differentiation. (A) Radial light micrograph of the retina of sablefish 97 days post-fertilization (dpf) following yolk-sac absorption. The relative position of cones in this developing retina was characteristic of all species studied except for the zebrafish. A red arrow points to the adjoining membrane complex between two members of a double cone (dc). (B) Schematic of the two morphological cone types [single cone (sc) and double cone] present in (A). (C) Tangential light micrograph of the retina in (A) showing the disposition of cones at the level of the inner segment ellipsoid. The lower part of the figure shows a square mosaic, where each single cone is flanked by four double cones. The area within the white rectangle diverges from the square mosaic pattern. (D, E) Radial (D) and tangential (E) light micrographs of the zebrafish retina at 15 dpf. The three cone types [double cone, long single cone (lsc), and short single cone (shsc)] occupy different tiers of the photoreceptor layer (D). The mosaic (E) spans double cone myoids to single cone outer segments. Ultrastructure details of the retinas from 97 dpf sablefish and 15 dpf zebrafish (panels A, C,D, E) are shown in Fig. 2. (F) Electron micrographs showing the disposition of single cones during their early morphological differentiation [the inner segment contains endoplasmic reticulum (er) and, when present, mitochondria (m)]. The mosaic schematics represent approximate tracings of cones, which are darkened. Each blue polygon links a cone’s immediate neighbours. (G, H) Micrographs and associated mosaic schematics of embryo or young larvae of the four altricial (G) and three precocial (H) species examined. The last column in each set of panels shows magnified views of the apposing plasma membranes between single cones (opposing white arrowheads); all are radial views except for the Senegalese sole panel. The white rectangle (asterisk) within the Atlantic halibut half-panel is magnified to its right. Days post-fertilization of the samples in (F–H) are indicated to the right of the panels. c connecting cilium, cn cone nucleus, cos cone outer segment, cpe cone pedicle, dcos double cone outer segment, hc horizontal cell, is inner segment, lcel long cone ellipsoid, lcos long cone outer segment, n nucleus, nu nucleus of retinal pigment epithelium cell, olm outer limiting membrane, os outer segment, pg pigment granule, rn rod nucleus, ros rod outer segment, rpe retinal pigment epithelium, rs rod spherule, shcel short cone ellipsoid. The magnification bar at the bottom left of (B) = 10 μm for (A–D) and 7.5 μm for (E). The magnification bar on the bottom right of each electron micrograph in (F–H) = 0.5 μm.
