Characterization of a paired box- and homeobox-containing quail gene (Pax-QNR) expressed in the neuroretina.

The retina is an integral part of the central nervous system, and consists of two layers, the outer pigmented layer and the inner sensory layer or neuroretina (NR). The NR layer contains several strata of cells (glial and neuronal) derived from proliferating neuroectodermal precursors that differentiate after terminal mitosis. In vitro, NR cells can differentiate not only into neuronal and glial types, but also into pigment and lens cells. Quail (Coturnix coturnix japonica) NR cells (QNR) infected with MC29 transforming retrovirus become pigmented after several passages in vitro. In order to characterize the genes expressed in these pigmented MC29 QNR, a cDNA library was prepared from these cells. After differential screening we have isolated a cDNA clone which identifies an RNA expressed in NR but not in the pigmented layer of the retina. This cDNA encodes a protein related to that of Drosophila, mouse and zebrafish paired box- and homeobox-containing segmentation genes and is called Pax-QNR. The expression of Pax-QNR in the NR is confined to the ganglionic cell layer and to the lower part of the inner nuclear layer containing the amacrine or correlation neurones.