Are miRNAs the key to retinal degeneration?

Absence of a specific RNase III endonuclease in the retina causes no immediate structural abnormalities but does prompt total retinal inactivity, according to a study published in the May 7 2008 issue of the Journal of Neuroscience.

Devid Damiani of the Neuroscience Institute, Pisa, Italy and colleagues removed one or both alleles of Dicer, essential for the production and function of mature miRNAs, from the retinas of mice embryos.

The mice with both Dicer alleles removed were born with fully formed retinas that displayed abnormally low electrical activity. By day 16, photoreceptor rosettes had formed; various retinal cell types continued to degenerate and scotopic and photopic responses to electroretinogram (ERG) testing decreased progressively at one, three and five months. Mice with a single allele of Dicer removed registered compromised ERG responses but retinas remained structurally sound throughout life. Retinas with depleted levels of Dicer had lower levels of several different miRNAs.

The researchers concluded that, since removing Dicer prompts gradual retinal degeneration in morphologically correct cells, it is possible that miRNAs are implicated in neurodegenerative disorders.