Type-I and type-II cholinergic amacrine cells express Islet1 throughout embryonic development, whereas type-III cells do not. Vertical sections of chick retina labeled with antibodies to Islet1 (green) and ChAT (red). Tissues were obtained from chicks at E6 (a-e), E7 (f-h), E9 (i-k), E11 (l-n), and P7 (o). Arrows indicate cells that are labeled for ChAT and Islet1, and arrow-heads indicate type-III cells that are immunoreactive for ChAT alone. The calibration bar (50 μm) in panel k applies to panels a, b, f-k and o, and the bar in n applies to panels c-e and l-n. Abbreviations: ChAT – choline acetyltransferase; INL – inner nuclear layer; IPL – inner plexiform layer; GCL – ganglion cell layer.