Detection and monitoring of microRNA expression in developing mouse brain and fixed brain cryosections.

MicroRNAs (miRNAs) are 20-25 nucleotide long, noncoding, and single-strand RNAs that have been found in almost all organisms and shown to exert essential roles by regulating the stability and translation of target mRNAs. In mammals most miRNAs show tissue specific and developmentally regulated expression. Approximately 70 % of all miRNAs are expressed in the brain and a growing number of studies have shown that miRNAs can modulate both brain development function and dysfunction. Moreover, miRNAs have been involved in a variety of human pathologies, including cancer and diabetes and are rapidly emerging as new potential drug targets. In order to further characterize miRNA functions, it is therefore crucial to develop techniques enabling their detection in tissues (both fixed and in vivo) with single-cell resolution. Here, we describe methods for the detection/monitoring of miRNA expression, that can be applied in both developing embryos and fixed samples, which we and others have applied to the investigation of both embryonal and postnatal neurogenesis in mice, but also in zebrafish, and cell cultures.