Figure 2.

Photomicrographs of transverse sections of retina of small larval lampreys stained with H-E (A–C) or immunostained for DCX (D–I). (A) Retina of an early larva (20 mm), in which only the central retina is present. Note also the presence of the retinal pigment epithelium (asterisk) and the crystalline lens (L). (B) Retina of a 40 mm larva, which shows the central and lateral retinas. (C) Central and lateral retinas in a larva of 75 mm. Dash lines mark the limit between the central and lateral retinas in (B,C) and also between the central and peripheral regions of the lateral retina in (C; see Villar-Cheda et al., 2008). Dotted lines mark the limits between layers in the central retina in (C). (D) DCX immunoreactivity is observed in the perikarya of photoreceptors (thin arrow), in fibers of the inner plexiform layer (IPL) and in round cells located in the ventral retina, close to the exit of the optic fibers (thick arrow) in a 20 mm larva. (E) DCX immunoreactivity in a 40 mm larva. Expression is observed in the perikarya and the outer segments of photoreceptors, in fibers of the IPL and in cells of the outer layer of the inner nuclear layer (INL). The DCX-ir retinal pigment epithelium is indicated with an asterisk. (F) Retina of a 70 mm larva showing DCX immunoreactivity in the perikarya and outer segments of photoreceptors, in fibers of the optic nerve (ON) and in cells and fibers of the INL and IPL, respectively. (G) Detail of the central retina of a 40 mm larva. (H) Retina of a 40 mm larva showing DCX immunoreactivity in round cells of the ventral retina located close to the ON. (I) Detail of the retina of a 70 mm larva showing DCX-ir radial processes (arrowhead) in the boundary between the central and lateral retina. Note the absence of DCX immunoreactivity in the lateral retina. In all photomicrographs dorsal is up and medial is to the left. Scale bars: 25 μm in (A,D,G,I); 50 μm in (B,C,E,F,H).