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L. Hackler, Jr., J. Wan, J. Qian, D. J. Zack; MicroRNA Transcriptome of the Postnatal Nrl -/- Mouse Retina. Invest. Ophthalmol. Vis. Sci. 2009;50(13):477.
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Micro RNAs (miRNAs) are small highly conserved non-coding molecules of 18-24nt length. They function as negative regulators of gene expression by destabilizing protein coding messenger RNAs or by inhibiting protein translation. The goal of our study was to identify sets of miRs whose expression varies during retinal development and additionally to define photoreceptor cell type specificity of miR expression through comparison of rod (wild type) and cone dominant (Nrl -/-) retinas.
Total RNA was isolated with Trizol (Invitrogen) from retinas of postnatal day 1 (P1), 5 (P5), 12 (P12) and 3 month old (adult) Nrl -/- and 3 month old (adult) C57BL/6 mice. All samples were hybridized onto in house printed miRNA arrays containing LNA probes for mouse miRNA sequences (Exiqon). A reference sample design was used to enable indirect comparison and for normalization purposes. After data normalization, hierarchical clustering was carried out to analyze characteristic miRNA expression profiles. Expression data was validated by quantitative real time PCR.
Expression data reveals that similar numbers of miRNAs are expressed in adult WT and Nrl null retinas (at least 112 and 104, respectively). Of these, a small number of microRNAs are differentially expressed between WT and Nrl -/- retinas. No miRNAs were identified that are totally specific to WT or Nrl null retinas. Hierarchical cluster analysis identified sets of miRNAs peaking at each of the investigated time point. Three major expression profiles were identified: 1) increasing expression with time; 2) decreasing expression with time; and 3) peak expression at an intermediate time point.
Our studies identified miRNAs that are differentially expressed between a rod and cone dominant retina, presumably reflecting either differences in the rod and cone miRNA transcriptome or the effect of these cells on their environment. Although increasing information is available about miRNAs in the context of the retina, the cell type specificity of expression of miRNAs in the retina is still only poorly understood. Hopefully increasing such knowledge will provide a useful step in understanding the function of miRNAs in retinal development and function.
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