Ultramicroscopical immunolocalization of PAX6 in the adult chicken retina

Cell type-specific PAX6 protein expression was examined in all retinal layers of the normal chicken retina. The most intense PAX6 immunostaining was found in the ganglion cell and inner nuclear layers, and in lower amounts in the optic nerve fiber, the inner plexiform and the photoreceptor layers. PAX6 immunostaining was variable in terms of its subcellular localization, even within one cell. PAX6 immunostaining was mainly localized in nuclear heterochromatin of the ganglion cell and inner nuclear layers whereas in the outer nuclear layer, PAX6 immunostaining was only observed in the intercellular space and the cytoplasm. In photoreceptors, the myoid portion of the inner segment showed PAX6 immunostaining, but the ellipsoid portion and the outer segment did not. The ultrastructural distribution pattern of PAX6 in the adult chicken retina suggests that normal expression of PAX6 is variable even in subcellular structures in the same cell type.