Correlation of Bestrophin Protein Expression in the Basolateral Plasma Membrane of the Mouse RPE with the Onset of Photoreceptor Activity in the Retina

Abstract

Abstract: : Purpose: Best macular dystrophy is an autosomal dominant disease, caused by mutations in the VMD2 gene that encodes the protein bestrophin. To increase our understanding of the function of bestrophin, the onset of bestrophin expression was followed in mouse eyes during development. Methods:BALBc mice were examined at different embryonic (E) and postnatal (P) ages. Bestrophin mRNA was quantified using Taq-man quantitative PCR. Immunohistochemistry for mouse bestrophin was performed on paraffin-embedded sections, using a polyclonal mouse bestrophin antibody produced by immunizing rabbits with a peptide corresponding to the mouse bestrophin C-terminus. Electroretinograms were recorded from the corneal surface of mice beginning at P8, to strobe flashes after overnight dark adaptation. Results: Bestrophin mRNA was detected as early as E15. Bestrophin protein expression in the RPE was not observed until P10 at which time it was observed to localize to the basolateral membrane of the RPE. The earliest age at which an a-wave could be recorded from mouse eyes was P10, coincident with the onset of bestrophin protein expression in the RPE. Conclusions: Despite the presence of mRNA for Bestrophin during embryonic development, the onset of protein expression in RPE is late, beginning at P10. This coincides with the onset of photoreceptor electrical activity, supporting the hypothesis that bestrophin plays a role in the RPE electrical responses to phototransduction. In addition, we conclude that bestrophin protein is a late marker for RPE differentiation.

Keywords: proteins encoded by disease genes • retinal development • immunohistochemistry