A GOLDFISH NOTCH-3 HOMOLOG IS EXPRESSED IN NEUROGENIC REGIONS OF EMBRYONIC, ADULT, AND REGENERATING BRAIN AND RETINA

Members of the Notch gene family are thought to be involved in the reg ulation of cell fate decisions in a variety of embryonic tissues, part icularly in the developing central nervous system (CNS) in Drosophila and vertebrates. In goldfish the CNS continues to develop and add neur ons well into adulthood and has the capacity to regenerate new neurons . Using probes derived from Xenopus Notch to screen an adult goldfish retinal cDNA library, followed by 5' RACE, we isolated a partial cDNA For a goldfish Notch homologue, G-Notch. Sequence alignment supported assignment of G-Notch to the Notch-3 class. Northern blot analysis rev ealed a single transcript of >8 kb, and RNase protection assays indica ted that G-Notch is expressed in eye and brain but not muscle of adult goldfish. The spatiotemporal pattern of expression of G-Notch was def ined from early embryonic stages to adulthood by in situ hybridization . Expression in the embryonic CNS was localized to neurogenic regions and was downregulated in differentiated cell populations. In adult gol dfish, expression persisted in and adjacent to the germinal zones in t he retina and the brain. Weak expression was seen in scattered cells i n the inner nuclear layer of the retina, which might include neurogeni c stem cells. Following retinal lesions (puncture wounds or laser lesi ons restricted to photoreceptors in the outer nuclear layer), G-Notch was upregulated in proliferating cell populations throughout the retin a, in association with a generalized mitogenic response. In the region of the laser lesion, where earlier studies have demonstrated that pho toreceptors are regenerating at 1-3 weeks Following the lesion, G-Notc h expressing cells were abundant in the outer nuclear layer. These obs ervations suggest that retinal regeneration involves the re-expression of an important developmental signaling molecule in neuroepithelial c ells resident in the differentiated retina. (C) 1997 Wiley-Liss, Inc.