Loss of Gap Junction Delta-2 (GJD2) gene orthologs leads to refractive error in zebrafish

Wim H Quint,Magda Meester-Smoor,Caroline C W Klaver,H Martijn De Gruiter,Melanie Hoevenaars,Adam C Miller,Rob Willemsen,Erwin Van Wijk,Sanne Broekman,Beerend H J Winkelman,Rachel M Lukowicz,Frank Schaeffel,Adriana I Iglesias,Erik De Vrieze,Kirke C D Tadema

doi:10.1038/s42003-021-02185-z

Abstract

Myopia is the most common developmental disorder of juvenile eyes, and it has become an increasing cause of severe visual impairment. The GJD2 locus has been consistently associated with myopia in multiple independent genome-wide association studies. However, despite the strong genetic evidence, little is known about the functional role of GJD2 in refractive error development. Here, we find that depletion of gjd2a (Cx35.5) or gjd2b (Cx35.1) orthologs in zebrafish, cause changes in the biometry and refractive status of the eye. Our immunohistological and scRNA sequencing studies show that Cx35.5 (gjd2a) is a retinal connexin and its depletion leads to hyperopia and electrophysiological changes in the retina. These findings support a role for Cx35.5 (gjd2a) in the regulation of ocular biometry. Cx35.1 (gjd2b) has previously been identified in the retina, however, we found an additional lenticular role. Lack of Cx35.1 (gjd2b) led to a nuclear cataract that triggered axial elongation. Our results provide functional evidence of a link between gjd2 and refractive error.

Highlights

Myopia is the most common developmental disorder of juvenile eyes, and it has become an increasing cause of severe visual impairment
To prevent biases induced by potential differences in the mean body sizes of gjd2a (Cx35.5) and gjd2b (Cx35.1) mutants, we compared these fish to wild type (WT) controls that matched the mean body length of the mutant group within a 10% range
We measured the ocular biometry with spectraldomain optical coherence tomography (SD-OCT) and defined axial length as the distance from the apical part of the corneal epithelium to the anterior part of the retinal pigmented epithelium (RPE)

Summary

Introduction

Myopia is the most common developmental disorder of juvenile eyes, and it has become an increasing cause of severe visual impairment. Our immunohistological and scRNA sequencing studies show that Cx35.5 (gjd2a) is a retinal connexin and its depletion leads to hyperopia and electrophysiological changes in the retina These findings support a role for Cx35.5 (gjd2a) in the regulation of ocular biometry. In 2010, one of the first GWAS for RE in European populations identified a locus near the gap junction protein delta-2 (GJD2) gene, harboring regulatory elements that could potentially influence the transcription of GJD24 After this initial discovery, the association of this locus to myopia has been replicated by multiple independent studies in numerous ethnicities[5,6,7,8,9,10,11,12,13,14,15]. Our results suggest that both gjd2a (Cx35.5) and gjd2b (Cx35.1) are expressed in the retina, and that loss of function leads to alterations in ocular biometry and development of RE

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