Impact of ?-crystallin protein loss on zebrafish lens development

The alpha-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 cataracts, the leading cause of human blindness. There are conflicting data in the literature as to what role the alpha-crystallins may play in early lens development. In this study, we used CRISPR gene editing to produce zebrafish lines with mutations in each of the three alpha-crystallin genes (cryaa, cryaba and cryabb) to prevent protein production. The absence of each alpha-crystallin protein was analyzed by mass spectrometry, and lens phenotypes were assessed with differential interference contrast microscopy and histology. Loss of alpha A-crystallin produced a variety of lens defects with varying severity in larvae at 3 and 4 dpf but little substantial change in normal fiber cell denucleation. Loss of alpha Ba-crystallin produced no substantial lens defects. Our cryabb mutant produced a truncated alpha Bb-crystallin protein and showed no substantial change in lens development. Mutation of each alpha-crystallin gene did not alter the mRNA levels of the remaining two, suggesting a lack of genetic compensation. These data suggest that alpha Acrystallin plays some role in lens development, but the range of phenotype severity in null mutants indicates its loss simply increases the chance for defects and that the protein is not essential. Our finding that cryaba and cryabb mutants lack noticeable lens defects is congruent with insubstantial transcript levels for these genes in lens epithelial and fiber cells through five days of development. Future experiments can explore the molecular mechanisms leading to lens defects in cryaa null mutants and the impact of alpha A-crystallin loss during zebrafish lens aging.

Automated summary

Alpha-crystallin small heat shock proteins play a role in maintaining the transparency and refractive properties of the eye lens, and their absence can lead to lens defects. In this study, zebrafish lines with mutations in the alpha-crystallin genes were generated using CRISPR gene editing. Loss of alpha A-crystallin resulted in various lens defects, while loss of alpha Ba- and alpha Bb-crystallin did not cause noticeable lens abnormalities. These findings suggest that alpha A-crystallin plays a role in lens development, but its loss is not essential. The study also highlights the need for further research on the molecular mechanisms behind lens defects and the impact of alpha A-crystallin loss in aging zebrafish lenses.