Effects of α-crystallin gene knockout on zebrafish lens development

The α-crystallin small heat shock proteins contribute to the transparency and refractive properties of the vertebrate eye lens and prevent the protein aggregation that would otherwise produce lens cataract, the leading cause of human blindness. There are conflicting data in the literature as to what role the α-crystallins may play in early lens development. In this study we used CRISPR gene editing to produce zebrafish lines with null mutations for each of the three α-crystallin genes ( cryaa , cryaba and cryabb ). Absence of protein was confirmed by mass spectrometry and lens phenotypes were assessed with differential interference contrast microscopy and histology. Loss of αA-crystallin produced a variety of lens defects with varying severity in larval lenses at 3 and 4 dpf, but little significant change in normal fiber cell denucleation. Loss of either αBa- or αBb-crystallin produced no significant lens defects. Mutation of each α-crystallin gene did not alter the expression levels of the remaining two, suggesting a lack of genetic compensation. These data confirm a developmental role for αA-crystallin in lens development, but the range of phenotype severity suggests its loss simply increases the chance for defect, and that the protein is not essential. Our finding that cryaba and cryabb null mutants lack noticeable lens defects is congruent with insignificant transcript levels in lens epithelial and fiber cells. Future experiments can explore the molecular consequences of cryaa mutation and causes of lens defects in this null mutant, as well as the roles of other genes in lens development and function. ### Competing Interest Statement The authors have declared no competing interest.