Expression of a 12-kb promoter element derived from the zebrafish enolase-2 gene in the zebrafish visual system

We recently cloned the zebrafish neuronal enolase-2 gene and showed that a 12-kb eno2 promoter element was sufficient to drive transgene expression widely in CNS neurons in vivo from 48h post-fertilization through adulthood. The aim of the present study was to establish the expression pattern of the 12-kb eno2 promoter element in the zebrafish visual system. Endogenous eno2 mRNA was detected in the developing retina from 2 days post-fertilization (dpf), and by 12dpf was localized to the retinal ganglion cell, inner and outer nuclear layers. Similar to endogenous eno2, GFP expression in the retina of Tg(eno2:GFP) larvae was first evident at 2dpf, and by 12dpf intense GFP expression was seen in the retinal ganglion cell and photoreceptor layers, with weaker expression in the inner nuclear layer. We identified cell types expressing the eno2 promoter element by using two complementary strategies: (i) double label immunofluorescence analysis of Tg(eno2:GFP) zebrafish, and (ii) generation of double transgenic zebrafish expressing red fluorescent protein under transcriptional control of the 12-kb eno2 promoter and GFP under a rod- or cone-specific promoter. The 12-kb eno2 promoter was expressed in retinal ganglion cells, amacrine cells, including a subset that co-expressed tyrosine hydroxylase, and rod photoreceptors. These data suggest that abnormalities of vision should be sought in transgenic models of diseases generated using this promoter. Owing to the specific expression of fluorescent reporters in neuronal subpopulations, Tg(eno2:GFP) and Tg(eno2:mRFP) zebrafish may be useful for studies of retinal lamination, neuronal differentiation and synapse formation in the visual system.