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A. Froger, K. Németh-Cahalan, K. Kalman, J. E. Hall; Charaterization of Two Novel Zebrafish AQP0s, Zeb1-AQP0 and Zeb2-AQP0. Invest. Ophthalmol. Vis. Sci. 2007;48(13):2812.
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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 tight junctions. However the involvement of AQP0 in lens development and function is not entirely understood. The development and morphology of the eye are conserved among vertebrates including zebrafish (Danio rerio). Zebrafish is an excellent model for studying ocular development, function and disease. Consequently we searched for a zebrafish AQP0 homologue as a first step in exploiting the zebrafish model to investigate the role of AQP0 in lens development and homeostasis.
We used MIPfun, the only functionally characterized fish AQP0 from killifish, as the query sequence in BLAST searches. We performed sequence comparison using alignments and dendrogramms of AQP0 proteins. We expressed the zebrafish candidate genes in Xenopus oocytes and measured their water permeability in response to an osmotic challenge.
The BLAST searches revealed that whereas mammalian genomes contain only one AQP0 gene, the zebrafish genome contains two AQP0 genes (Zeb1-AQP0 and Zeb2-AQP0). Zeb1-AQP0 and Zeb2-AQP0 are 93% and 85% identical to MIPfun respectively, and 84% identical to each other. We investigated the hypothesis that the function or/and expression pattern of the single mammalian AQP0 is divided between two AQP0s in Zebrafish. When expressed in Xenopus oocytes Zeb1-AQP0 and Zeb2-AQP0 were both functional water channels. Zeb1-AQP0 water permeability was similar to MIPfun’s whereas, Zeb2-AQP0 water permeability was 50% less.
Zebrafish is the first species known to express two different AQP0s. Numerous studies have shown that a genome duplication occurred in the ancestry of teleost fish and that at least 20% of duplicated gene pairs may have been retained. However the preservation of both duplicates often leads to divergence of function or expression pattern. We find that both Zeb1-AQP0 and Zeb2-AQP0 are functional aquaporins. The next step will be to disrupt the expression of each AQP0 in zebrafish embryos to better understand the role(s) of AQP0 during eye development.
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