Zonular defects in loxl1-deficient zebrafish

To investigate the roles of the lysyl oxidase-like 1 (loxl1) gene in zebrafish eye development and the potency of loxl1 deficiency in mimicking the ocular manifestations of exfoliation syndrome (XFS).

CRISPR/Cas9 technology was used to generate a frameshift coding deletion in zebrafish loxl1. Expression profiles and ocular manifestations of the wildtype, heterozygous mutant (loxl1^+/- ) and homozygous mutant (loxl1^-/- ) zebrafish were analysed in a range of developmental stages from zebrafish larvae to dissected adult zebrafish eyes.

The loxl1 deficiency caused zonular bundling disorders in juvenile zebrafish and accumulation of pearl-like particles adhering to the adult zebrafish zonule. The bundles appeared to lack form and were thinner in both loxl1^+/- and loxl1^-/- zebrafish compared with the wildtype (p < 0.01 for all Bonferroni post-hoc analyses). The zonule of loxl1^-/- zebrafish appeared stretched, ragged and torn, with isolated fibres also detected. The particles in loxl1^-/- zebrafish were more numerous (counts: 92.33 ± 10.02/100 μm² vs. 58.33 ± 5.03/100 μm² , p = 0.006), but smaller in size (diameter: 0.21 ± 0.03 μm vs. 0.43 ± 0.04 μm, p = 0.002) compared with those in loxl1^+/- . Transmission electron microscopy revealed thinning or even loss of elastic lamina in loxl1^+/- Bruch's membrane (BM) (thickness of elastic lamina: 92.94 ± 18.19 nm in the wildtype vs 35.65 ± 14.76 nm in loxl1^+/- , p = 0.003). The breakage of BM was observed in loxl1^-/- .

The loxl1^-/- zebrafish is a promising animal model of XFS zonular pathology.