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A. Froger, K. Németh-Cahalan, K. Kalman, T. F. Schilling, J. E. Hall; Knockdown of Zeb1-AQP0 or Zeb2-AQP0 Leads to Cataract Formation in Zebrafish. Invest. Ophthalmol. Vis. Sci. 2008;49(13):3170. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To determine the roles of AQP0 in lens function and development. Two functions have been proposed for Aquaporin 0 (AQP0) in the mammalian lens: water transport and formation of thin junctions. Interestingly whereas mammalian genomes contain only one AQP0 gene, the zebrafish genome contains two, Zeb1-AQP0 and Zeb2-AQP0. Consequently we propose the hypothesis that one AQP0 could be a water channel whereas the other could be a junction protein.
Whole-mount in situ hybridization (WMISH) was performed with digoxigenin-labeled antisense RNA Zeb1-AQP0 and Zeb2-AQP0 probes. Antibodies specific for Zeb1-AQP0 and Zeb2-AQP0 were raised and used to determine the expression of the proteins in adult zebrafish lens membranes. Antisense morpholinos were microinjected into zebrafish embryos to inhibit Zeb1-AQP0 and/or Zeb2-AQP0 gene expression. cRNA were expressed in Xenopus oocytes and the water permeability measured in response to an osmotic challenge.
Using WMISH and western blots we detected expression of both genes in embryonic and adult lens. In zebrafish embryos both genes are expressed only in lens as in mammals. Disruption of Zeb1-AQP0 and/or Zeb2-AQP0 expression with morpholinos resulted in central cataract formation at 3 days post fertilization. When expressed in Xenopus oocytes Zeb1-AQP0 was a water channel whereas Zeb2-AQP0 was not.
Zebrafish is an excellent model for studying ocular development, function and disease. Zebrafish is the first species known to express two AQP0 genes. Numerous studies have shown that a genome duplication occurred in the ancestry of teleost fish. However the preservation of both duplicates often leads to divergence of function or expression pattern. Zeb1-AQP0 and Zeb2-AQP0 are both expressed exclusively in the lens as soon as the lens develops and also in adult. Their similar expression pattern suggests a divergence in function and indeed Zeb1-AQP0 or Zeb2-AQP0 knockdown leads to cataract formation proving that they are both necessary for lens transparency and that their functions are not redundant. We find that Zeb1-AQP0 is a functional aquaporin whereas Zeb2-AQP0 is not under the conditions we tested.
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