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S. M. Nelson, R. A. Frey, S. Wardwell, D. L. Stenkamp; A Functional Role for the Retinal Homeobox 1 (rx1) Transcription Factor in Zebrafish Photoreceptor Development. Invest. Ophthalmol. Vis. Sci. 2007;48(13):4470.
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Rx genes have been associated with anophthalmia and retinitis pigmentosa. The expression of zebrafish rx1 has been demonstrated in cones but not rods (Chuang et al., Mech. Dev., 84, 195-198, 1999). Recently, the functional knockdown of rx1 was shown to result in a reduction in cells of the outer nuclear layer (Rojas-Muñoz et al., Dev. Biol., 288, 348-362, 2005). We wished to determine if 1) rx1 is expressed in embryonic rods and/or cells of the rod lineage and 2) if the selective knockdown of rx1 expression has specific effects on rod and cone development.
1) Double in situ hybridization was used to evaluate co-expression of rx1 with other transcription factors expressed in the rod lineage. 2) Embryos were injected at the 1-2 cell stage with rx1 antisense morpholino oligonucleotides and the expression of cell specific markers was visualized using immunocytochemical techniques.
1) Rx1 was co-expressed with several rod lineage markers including NeuroD, crx, and rod opsin. 2) Embryos treated with rx1 morpholinos showed a reduction in rod and cone specific markers. The most severely affected individuals showed no detectable photoreceptor labeling. Expression of ganglion cell, rod bipolar cell, and Müller glial cell specific markers was also reduced. Pronounced lamination defects and increased cell death were also observed.
Rx1 is expressed in cells of the rod lineage and may play a functional role in the development of both rod and cone photoreceptors. However, rx1 also is expressed early in development and plays a role in the establishment of the eye field (Chuang et al., 1999). To understand the specific role of rx1 in photoreceptor development, a temporally selective knockdown strategy is needed at a time prior to photoreceptor neurogenesis. We introduce the nanowire-mediated delivery of morpholinos as a potential solution to this problem.
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