Characterization of the RNA-binding protein Rbfox1 in the Mouse Retina

Abstract

Purpose : The Rbfox1 (RNA-binding protein, fox-1 homolog) splicing and transcription factor has been identified earlier with gene expression profiling of retinal ganglion cells (RGCs). The present study evaluates the expression pattern of Rbfox1 in developing and adult mouse retina as well as its function in Rbfox1 knockout animals.

Methods : E12, E15, P0, P5, P21 and adult wild type mouse retinas were used for the cellular localization of Rbfox1 protein. Retinal whole mount immunostaining was used for quantitative analysis of Rbfox1-positive cells. Adult Rbfox1^loxP/loxP/Ubiquitin-Cre^+/- transgenic mice were used for tamoxifen-induced conditional deletion of the Rbfox1. The effect of Rbfox1 ablation on retinal morphology and cell numbers was analyzed eight weeks after tamoxifen administration. The functional integrity of the retino-geniculo-cortical pathway was evaluated with the visual cliff test.

Results : Rbfox1 immunoreactivity was observed in the ganglion cell layer (GCL) of the developing retina at E12, and became more prominent at E15. Rbfox1 immunolabelling extended from the GCL to the inner nuclear layer (INL) at P0 and starting at P5, Rbfox1-expressing cells were clearly colocalized with Rbpms-positive RGCs in the GCL and calbindin-positive amacrine cells (ACs) in the GCL and INL. Whole mount immunostaining of the adult mouse retinas showed that very nearly 100% of RGCs and ACs express Rbfox1. Conditional deletion of the Rbfox1 was used to evaluate the function of this gene in the retina. Rbfox1^loxP/loxP/Ubiquitin-Cre^+/- mice were viable with normal size and weight but had reduced fertility compared to Rbfox1^+/- or wild-type littermates. As expected, Rbfox1 expression in RGCs and ACs of Rbfox1^-/- animals was dramatically reduced. No evidence of morphological changes in the retinas of Rbfox1 knockout mice was observed and the average RGC and AC densities in these animals were comparable to that of controls. However, the sensitivity of visual depth perception of Rbfox1^-/- mice was reduced by approximately 75%.

Conclusions : Rbfox1 expression in RGCs and ACs starts at early stages of their differentiation and remains strong in these cells in fully developed retinas. Although no morphological changes in the retinas of transgenic animals were detected eight weeks after deletion of Rbfox1, the deficiency of depth perception in these animals suggests a functional importance of this gene in vision processing.

This is an abstract that was submitted for the 2017 ARVO Annual Meeting, held in Baltimore, MD, May 7-11, 2017.