Aqp0a Regulates Suture Stability in the Zebrafish Lens

PURPOSE: To investigate the roles of Aquaporin 0a (Aqp0a) and Aqp0b in zebrafish lens development and transparency. METHODS: CRISPR/Cas9 gene editing was used to generate loss-of-function deletions in zebrafish aqp0a and/or aqp0b. Wild type (WT), single mutant, and double mutant lenses were analyzed from embryonic to adult stages. Lens transparency, morphology, and growth were assessed. Immunohistochemistry was used to map protein localization as well as to assess tissue organization and distribution of cell nuclei. RESULTS: aqp0a(−/−) and/or aqp0b(−/−) cause embryonic cataracts with variable penetrance. While lenses of single mutants of either gene recover transparency in juveniles, double mutants consistently form dense cataracts that persist in adults, indicating partially redundant functions. Double mutants also reveal redundant Aqp0 functions in lens growth. The nucleus of WT lenses moves from the anterior pole to the lens center with age. In aqp0a(−/−) mutants, the nucleus fails to centralize as it does in WT or aqp0b(−/−) lenses, and in double mutant lenses there is no consistent lens nuclear position. In addition, the anterior sutures of aqp0a(−/−), but not aqp0b(−/−) mutants, are unstable resulting in failure of suture maintenance at older stages and anterior polar opacity. Conclusions. Zebrafish Aqp0s have partially redundant functions, but only Aqp0a promotes suture stability, which directs the lens nucleus to centralize, failure of which results in anterior polar opacity. These studies support the hypothesis that the two Aqp0s subfunctionalized during fish evolution and that Aqp0-dependent maintenance of the anterior suture is essential for lens transparency.