Inactivation of the miR-183/96/182 Cluster Results In Photoreceptor Postnatal Developmental Arrest and Synaptic Defects, Leading to Retinal Dysfunction and Degeneration

Abstract

Purpose: Previously we identified a highly conserved, paralogous miRNA cluster, the miR-183/96/182 cluster (the miR-183C in short), which is highly, specifically expressed in the retina and all sensory organs. The purpose of current study is to uncover in vivo functions of this cluster in the retina.

Methods: Using a gene-trap embryonic stem cell clone, we generated a mouse model, designated as the miR-183C^GT/GT mice. Comprehensive characterization was performed by Northern blot, quantitative RT-PCR, X-gal, H&E staining, immunofluorescence (IF) and electron microscopy, scotopic and photopic electroretinograms (ERGs); gene-expression profiling. Light damage experiment was performed by exposing dark-adapted animals to 10,000 lux light for 2 hours.

Results: The miR-183C is inactivated in the retina and all other sensory organs of miR-183C^GT/GT. Expression of the β-geo cassette followed native expression patterns of the cluster in the retina and other sensory organs; and is highly specifically expressed in photoreceptors and a subgroup of ganglion cells in the retina. Functionally, miR-183C^GT/GT mice showed early onset, progressive abnormalities in both scotopic and photopic ERGs, with decreased b wave amplitude as the most prominent defect, suggesting photoreceptor synaptic defects. miR-183C^GT/GT mice showed slowly-progressing retinal degeneration, and increased susceptibility to light damage. Normal postnatal migration of cone photoreceptors in the outer nuclear layer was arrested in the miR-183C^GT/GTmice. The sizes of synaptic ribbons were significantly decreased in the miR-183C^GT/GT mice; In addition, the miR-183C^GT/GT mice demonstrate signs of obvious defects in vestibular function, suggesting dysfunctions in other sensory systems.

Conclusions: The miR-183C is required for postnatal functional differentiation including the development of synaptic ribbons of the photoreceptors; and is a candidate gene, contributing to early-onset and slowly progressive, syndromic retinal degenerative diseases. The synaptic defect of the retina of miR-183C^GT/GT mice is consistent with inner ear abnormalities of miR-96 mutants with hair cell development arrest and synaptic defects; suggesting that defining functional synaptic connections is a conserved function of the miR-183C in sensory organs.

Keywords: 648 photoreceptors • 696 retinal degenerations: hereditary • 740 transgenics/knock-outs