OL-protocadherin expression in the visual system of the chicken embryo

The expression of OL-protocadherin, a homotypically binding cell adhesion molecule, was mapped in the visual system of the chicken embryo at intermediate to late stages of development (11-19 days of incubation). The expression was compared with that of four classic cadherins, described previously. OL-protocadherin is expressed by the isthmooptic nucleus, its retinopetal projection, and possibly its retinal target neurons, the amacrine cells. Ganglion cells begin to express OL-protocadherin at relatively late stages of development. The layers of the optic tectum, the projection neurons in the stratum griseum centrale, and the tectofugal pathways show differential OL-protocadherin immunoreactivity. Several of the diencephalic target nuclei of the tectothalamic projection, such as the principal pretectal nucleus, subpretectal nucleus, and nucleus rotundus, contain distinct subregions or populations of neurons expressing OL-protocadherin. In these centers, the expression pattern of OL-protocadherin differs from that of the four classic cadherins, though it shows partial overlap with them. Other retinorecipient and/or tectorecipient nuclei (ventral geniculate nucleus, lateral dorsolateral nucleus, superficial synencephalic nucleus, pretectal area, and griseum tectale) also show a differential immunoreactivity for OL-protocadherin and other cadherins. Some of these nuclei and the optic tectum display a similar sequence of cadherin expression from superficial to deep layers, in a pattern that may reflect mutual interconnections. This result indicates a partial conservation of cadherin expression across interconnected embryonic divisions, from the mesencephalon to the ventral thalamus. In conclusion, OL-protocadherin is a marker for specific functional gray matter structures and neural circuits in the chicken visual system. J. Comp. Neurol. 470:240-255, 2004.