Although microRNAs (miRNAs) provide a newly recognized level of regulation of gene expression, the miRNA transcriptome of the retina and the contributions of miRNAs to retinal development and function are largely unknown. To begin to understand the functions of miRNAs in retina, we compared miRNA expression profiles in adult mouse retina, brain, and heart by microarray analysis. Our results show that at least 78 miRNAs are expressed in adult mouse retina, 21 of which are potentially retina-specific. Among these, we identified a polycistronic, sensory organ-specific paralogous miRNA cluster that includes miR-96, miR-182, and miR-183 on mouse chromosome 6qA3 with conservation of synteny to human chromosome 7q32.2. In situ hybridization showed that members of this cluster are expressed in photoreceptors, retinal bipolar and amacrine cells. Consistent with their genomic organization, these miRNAs have a similar expression pattern during development with abundance increasing postnatally and peaking in adult retina. Target prediction and in vitro functional studies showed that MITF, a transcription factor required for the establishment and maintenance of retinal pigmented epithelium, is a direct target of miR-96 and miR-182. Additionally, to identify miRNAs potentially involved in circadian rhythm regulation of the retina, we performed miRNA expression profiling with retinal RNA harvested at noon (Zeitgeber time 5) and midnight (Zeitgeber time 17) and identified a subgroup of 12 miRNAs, including members of the miR-183/96/182 cluster with diurnal variation in expression pattern. Our results suggest that miR-96 and miR-182 are involved in circadian rhythm regulation, perhaps by modulating the expression of adenylyl cyclase VI (ADCY6). MicroRNAs (miRNAs)3 are small, noncoding, regulatory RNAs of 18 -24 nucleotides in length found in all metazoans. Since their discovery in 1993, at least 100 different miRNA genes have been documented in the genomes of Drosophila and Caenorhabditis elegans and more than 250 in vertebrate genomes (1) with recent estimates as high as 800 (2). By influencing translation and stability of mRNAs, miRNAs contribute a newly recognized level of regulation of gene expression affecting a variety of biological processes. miRNAs are transcribed by RNA polymerase II as transcripts (pri-miRNAs) that are capped, polyadenylated, and spliced (3). pri-miRNAs fold into hairpin structures that are cleaved by an RNase III endonuclease, the Drosha-DGCR8 complex, to form 60 -70-nt stem loop intermediates known as pre-miRNA (1, 4, 5) that are transported from the nucleus by an Exportin 5-dependent mechanism. In the cytoplasm they are cleaved by a second RNase III endonuclease, Dicer, to yield double-stranded

miRNAs are involved in the pathogenesis of DR through the modulation of multiple pathogenetic pathways and may be novel therapeutic targets for the treatment of DR.

The microRNA-183/96/182 cluster is highly expressed in the retina and other sensory organs. To uncover its in vivo functions in the retina, we generated a knockout mouse model, designated "miR-183CGT/GT ," using a gene-trap embryonic stem cell clone. We provide evidence that inactivation of the cluster results in early-onset and progressive synaptic defects of the photoreceptors, leading to abnormalities of scotopic and photopic electroretinograms with decreased b-wave amplitude as the primary defect and progressive retinal degeneration. In addition, inactivation of the miR-183/96/ 182 cluster resulted in global changes in retinal gene expression, with enrichment of genes important for synaptogenesis, synaptic transmission, photoreceptor morphogenesis, and phototransduction, suggesting that the miR-183/96/182 cluster plays important roles in postnatal functional differentiation and synaptic connectivity of photoreceptors. M icroRNAs (miRNAs) are small, endogenous, noncoding, regulatory RNAs and represent a newly recognized level of gene-expression regulation (1-4). miRNAs have unique expression profiles in the developing and adult retina and are involved in normal development and functions of the retina in all species studied so far (5-12). miRNAs are dysregulated in the retina of retinal degenerative mouse models, suggesting their potential involvement in retinal degeneration (13,14). Conditional inactivation of dicer, an RNase III endonuclease required for miRNA maturation in cytosol (15), in the mouse retina resulted in alteration of retinal differentiation and optic-cup patterning, increased cell death, and disorganization of axons of retinal ganglion cells (16)(17)(18)(19), suggesting that miRNAs are important for normal development and functions of the mammalian retina. However, in vivo functions of individual miRNAs in the retina still are largely unknown.Previously, we identified a highly conserved, intergenic, sensory organ-specific, paralogous miRNA cluster, the miR-183/96/182 cluster (hereafter, miR-183/96/182), contained within an ∼4-kb genomic segment on mouse chr6qA3.3 (8, 9). In the adult retina, miR-183/96/182 is expressed specifically in all photoreceptors and in the inner nuclear layer (8, 10). Developmentally, its expression is minimal in the embryonic retina but increases dramatically after birth and peaks in the adult retina, suggesting a role for miR-183/ 96/182 in maturation and normal functioning of the adult retina (8, 9). Additionally, expression of miR-183/96/182 has a diurnal pattern, suggesting a potential role in rhythmic functions of the retina (8, 9). Recently, miR-183/96/182 also was shown to be light responsive, independent of the circadian cycle (20). Targeted deletion of miR-182 alone in mouse did not result in a discernible phenotype, suggesting functional compensation by miR-183 and miR-96 (21). Point mutations of miR-96 were reported to result in progressive, nonsyndromic hearing loss in both human (22) and mouse (23); however, there was no apparent retinal phenotype, an ob...

Purpose To determine whether β-amyloid (Aβ) deposition affects the structure and function of the retina of the APPswe/PS1ΔE9 transgenic (tg) mouse model of Alzheimer’s disease. Methods Retinas from 12–19 month-old APPswe/PS1ΔE9 tg and age-matched non-transgenic (ntg) littermates were single or double stained with thioflavine-S and antibodies against Aβ, glial fibrilar acidic protein (GFAP), microglial marker F4/80, choline acetyltransferase (ChAT) and syntaxin 1. Quantification of thioflavine-S positive plaques and retinal layer thickness was analyzed semi-quantitatively, whereas microglial cell size and levels of F4/80 immunoreactivity were evaluated using a densitometry program. Scotopic electroretinogram (ERG) recording was used to investigate retinal physiology in these mice. Results Thioflavine-S positive plaques appeared at 12 months in the retinas of APPswe/PS1ΔE9 tg mice with the majority of plaques in the outer and inner plexiform (IPL) layers. Plaques were embedded in the IPL strata displaying syntaxin 1 and ChAT. The number and size of the plaques in the retina increased with age. Plaques appeared earlier and in greater numbers in females than in male tg littermate mice. Microglial activity was significantly increased in the retinas of APPswe/PS1ΔE9 tg mice. Although we did not detect neuronal degeneration in the retina, ERG recordings revealed a significant reduction in the amplitudes of a and b waves in aged APPswe/PS1ΔE9 tg compared to ntg littermates. Conclusions The present findings suggest that Aβ deposition disrupts retinal structure and may contribute to the visual deficits seen in aged APPswe/PS1ΔE9 tg mice. Whether Aβ is involved in other forms of age-related retinal dysfunction is unclear.