HU PROTEIN AS AN EARLY MARKER OF NEURONAL PHENOTYPIC DIFFERENTIATION BY SUBEPENDYMAL ZONE CELLS OF THE ADULT SONGBIRD FOREBRAIN

The avian forebrain exhibits neurogenesis in adulthood, with neuronal production from ependymal/subependymal zone (SZ) precursor cells, To f ollow the commitment of newborn cells to neuronal lineage, we used the ir expression of the Hu family of neuronal RNA-binding proteins to ide ntify them before their migration from the SZ, Adult canaries were inj ected with [H-3]thymidine as a marker of DNA replication, sacrificed a fter varying intervals, stained for Hu, and autoradiographed, We found that Hu was not expressed by premitotic precursor cells, but rather a ppeared within hours in their neuronal progeny, which did not embark o n parenchymal migration until 4 to 7 days later, Hu was expressed by a ll neurons, but not glia, both in vivo and in vitro, as determined by ultrastructural analysis as well as co-localization of Hu and cell-typ e selective antigens, In addition, co-staining for flu and N-cadherin, whose expression is down-regulated on neuronal emigration from the SZ , revealed their initial co-expression by neuronal daughter cells stil l within the SZ, These results suggest that Hu expression may be used as a very early indicator of neuronal differentiation by SZ cells, Fur thermore, the data indicate that in the adult avian brain, neuronal ph enotype is established within hours of precursor mitosis, even though the neuronal daughter cells do not initiate parenchymal migration for at least 4 days thereafter, following their down-regulation of N-cadhe rin. (C) 1995 John Wiley & Sons, Inc.