Abstract
Purpose :
Microcoria, or congenital miosis, is a rare autosomal dominant ocular disorder characterized by dilator muscle fiber deficiency in the iris. It manifests as pinhole pupils (< 2 mm in diameter), iris hypopigmentation, and transillumination, resulting in hemeralopia and light hypersensitivity. Frequently associated with microcoria are juvenile-onset glaucoma, axial myopia, and astigmatism, which can progress to visual impairment or blindness without intervention. Submicroscopic deletions at 13q32.1, encompassing the SOX21 and GPR180 genes, have been linked to congenital microcoria in humans. This study employed zebrafish knockdown models of sox21b and gpr180 to investigate their functional roles.
Methods :
The CRISPR-Cas9 system, utilizing two guide RNAs, was used to knockdown (KD) sox21b and gpr180 via zebrafish embryo injection at one cell stage. Comparative analysis of the F0 crispants with random-guide-injected controls were conducted, focusing on eye, pupil, lens sizes, anterior chamber area, and corneal thickness at 5 days post-fertilization (dpf). Additionally, visual motor response (VMR) assays were performed at 5 dpf to evaluate the impact of sox21b and gpr180 KD on visual function.
Results :
Targeted editing of sox21b and gpr180 in F0 was verified using mismatch assay and next-generation sequencing. Sox21b crispants exhibited significantly smaller pupil (P<0.001), reduced anterior chamber area (P<0.01), corneal thickening (P<0.05), and iris abnormalities in comparison to controls. Moreover, sox21b crispants demonstrated a higher response to light-on stimuli (P<0.05) in the VMR assay, indicating a light hypersensitivity. Conversely, gpr180 crispants displayed only marginally smaller eye sizes compared to controls (P=0.01).
Conclusions :
In zebrafish, disruption of sox21b but not gpr180 results in developmental ocular phenotypes that recapitulate some clinical features observed in human congenital microcoria, supporting the use of zebrafish models in understanding the genetic mechanisms underlying microcoria and its association with glaucoma.
This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.