A number of miRNAs are expressed in highly tissue or stage-specific patterns while others are more broadly expressed. The CNS is by far the most complex organ of the mammalian body, and houses an impressive diversity of miRNAs. In fact, more than 50% of the known miRNAs have been detected in human and mouse brain. Moreover, miRNAs play an important role in modulating gene Bortezomib expression during neuronal development, from early neurogenesis to synaptogenesis, as well as in maintenance of neuron function. Dynamic changes in miRNA gene expression profiles have also been detected during brain development,. Therefore, the CNS is a particularly interesting target for miRNA studies. Various techniques, such as miRNA cloning, fluorescent in situ hybridization, northern blot, microarray, deep-sequencing and quantitative real-time PCR, have been successfully used for miRNA investigation. Currently, microarrays and deep sequencing are the most commonly used techniques for highthroughput profiling of miRNA expression. Quantitative real-time PCR is an extremely sensitive technique that enables validation of selected candidate miRNAs. Both microarray and qPCR can benefit from the Locked Nucleic Acid technology, which increases the thermal stability of the oligonucleotides. These techniques have been used successfully in various studies focused on analysis of miRNA expression in the CNS particularly in model organisms, such as the mouse. In one particular study investigating miRNA expression in mouse brain, 66 miRNAs showed altered expression levels during brain development. In addition, numerous miRNAs have been shown to be ubiquitously expressed in the CNS of mice. The majority of the reported miRNA research has been focused on disease-related studies in either human or rodents. However, there is a need to examine miRNAs further in other mammals, such as the domestic pig. The pig brain shows more similarity to the human brain, with respect to anatomy, size, growth and development, compared to brains of other laboratory animals, which makes the pig an important model to be considered within biomedical sciences. Therefore, it is highly relevant to generate knowledge about miRNA gene expression in pig tissues. This would provide useful comparative information between species. One further advantage in studying the pig is that tissues from different developmental stages are easily accessible. The normalization and data filtering resulted in 1088 high quality probe signals, which represented both human and porcine miRNAs. In the initial analysis of the data, we identified general similarities and differences between the samples by means of principal component analysis. The analysis of the microarray data in Figure 1 indicated, that the miRNA expression patterns within the cortex and cerebellum from gestation day 50 were highly similar to one other.