miRNA and Dicer in the mammalian lens: expression of brain-specific miRNAs in the lens.

Micro RNAs (miRNAs) are approximately 22 nucleotide molecules that regulate gene expression post-transcriptionally and govern a wide range of physiological and developmental processes. Evidence now indicates that miRNAs can also coordinately down-regulate transcript levels for very large groups of genes in a tissue-specific manner, in addition to their ability to suppress protein translation. Here, we examine expression of specific miRNAs and Dicer ribonuclease that is required for miRNA biogenesis in mouse and rat lenses. Northern blot analysis demonstrated lens expression of brain-specific miR-124 and miR-7 in lenses, as well as miR-125b and let-7a. In addition, we provide evidence that muscle specific miR-1 is not present in lens. We detected Dicer transcripts in 21 day, 6 week, and 1 year mouse lenses and 15 day rat lens, and detected Dicer protein in adult lens protein samples. Immunohistochemical examination of late embryonic, post-natal, and adult rat lens sections identified expression of Dicer in differentiating fiber cells that undergo pronounced cell elongation in the lens interior and anterior epithelial cells. The present study provides evidence that miRNAs, which include brain-specific forms, and Dicer are expressed in mammalian lenses, indicating that fundamental aspects of miRNA biology are utilized by the lens during late embryonic and post-natal development and in adult lenses.