EXPRESSION OF THE BZIP TRANSCRIPTION FACTOR GENE NRL IN THE DEVELOPING NERVOUS-SYSTEM

Proteins of the Maf/Nrl subfamily of bZIP transcription factors are in volved in the regulation of tissue-specific gene expression. The Nrl g ene, initially identified from a subtracted retinal library, is expres sed in all cell layers of the adult retina, including photoreceptors. The Nrl protein has high sequence homology with Maf proteins, binds to an AP-1 like sequence element, and in photoreceptors appears to be in volved in regulating the expression of rhodopsin. In the present study , we investigated the expression of Nrl in the developing and adult mo use using in situ hybridization and RT-PCR. We demonstrate that beginn ing at embryonic day 12.5 Nrl is expressed throughout the developing c entral and peripheral nervous system, with the exception of the nasal epithelium. The spatial pattern of hybridization suggests that Nrl is transcribed in post-mitotic, differentiating neurons, the developing c ephalic mesenchyme and lens. Nrl expression is downregulated postnatal ly in the brain, and becomes restricted to neocortex and brainstem in the adult. High levels of Nrl transcripts, however, persist in the mat ure photoreceptors and other retinal neurons. Our studies suggest a ro le for the Nrl protein in neuronal differentiation and in mature neuro ns of the adult retina.