MicroRNA (miRNA) transcriptome of mouse retina and identification of a sensory organ-specific miRNA cluster

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).