WNT2B deficiency leads to ectopic photoreceptor formation in mice

Abstract

Purpose : Wnt/β-catenin signaling is essential for embryonic eye development, and dysregulation of this system may lead to abnormal formation of both the anterior eye and retina. WNT2B, a ligand and activator of the Wnt/β-catenin pathway, assists in the development of the lens and peripheral regions of the eye. Humans with WNT2B deficiency have a range of ocular defects including microcornea and colobomas. WNT2B may also assist in retinal progenitor cell differentiation, yet the potential role of WNT2B in retinal vascular or neuronal development is understudied. This project explored the effects of WNT2B on retinal neuronal and vascular formation using Wnt2b-deficient mice.

Methods : Systemic Wnt2b knockout mice were generated by crossing Wnt2b^flox/flox (fl/fl) mice with CMV-cre mice to deplete Wnt2b in all tissues. Adult heterozygous (Het) and homozygous (KO) Wnt2b-deficient mice (cre+) were examined and compared to fl/fl mice (cre-) as controls. Eyes were either fixed for retinal flat mount or frozen for cross sectioning. Retinal vascular morphology was assessed in flat mounts with isolectin (vascular endothelium marker) staining. Retinal neuronal morphology was assessed with H&E staining of frozen cross sections. Retinal cell type was determined via immunohistochemical staining with either rhodopsin antibody (photoreceptor marker) or isolectin, and co-stained with DAPI (nuclei marker).

Results : Both Wnt2b Het and KO mice exhibited relatively normal anterior segments with normal shape and size of the iris and lens when compared to fl/fl mice. Formation of retinal blood vessels in both Het and KO mice also appeared normal in both superficial and deep vascular layers. In retinal cross section, large clusters of ectopic cells were observed in the subretinal space around the photoreceptor inner and outer segments in both Wnt2b Het (3 out of 4 mice) and KO (2 out of 4 mice), while fl/fl retinas (from 4 mice) showed normal neuronal layers. Other neuronal layers of Het and KO eyes showed normal organization in both layer thickness and lamination, with no sign of retinal degeneration. The displaced cells were present in 2-month-old and persisted in 5-month-old Het and KO mice and stained positive for rhodopsin antibody while negative for isolectin, suggesting ectopic rod photoreceptor formation.

Conclusions : Our findings suggest that WNT2B is a novel regulator of photoreceptor formation and/or migration during eye development.

This is a 2021 ARVO Annual Meeting abstract.