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High-throughput sequencing has allowed for a comprehensive small RNA (sRNA) expression analysis of numerous tissues in a diverse set of organisms. The computational analysis of the millions of generated sequencing reads has led to the discovery of novel miRNAs and other sRNA species, and resulted in a better understanding of the roles these sRNAs play in development and disease. This chapter describes the generation of sRNA deep-sequencing libraries for the Illumina massively parallel sequencing platform by using a cloning method that anneals specific RNA sequences to the 5'- and 3'-ends of the sRNA molecules.

Our understanding of the importance of noncoding RNA molecules is steadily growing. One such important class of RNA molecules are microRNAs (miRNAs). These tiny RNAs fulfill important functions in cellular behavior by influencing the protein output levels of a high variety of genes through the regulation of target messenger RNAs. Moreover, miRNAs have been implicated in a wide range of diseases. In pathological conditions, the miRNA expression levels can be altered due to changes in the transcriptional or posttranscriptional regulation of miRNA expression. On the other side, mRNA molecules might be able to escape the regulation by miRNAs. In this review, we give an overview on how miRNA biogenesis can be altered in disease as well as how mRNAs can avoid the regulation by miRNAs. The interplay between these two processes defines the final protein output in a cell, and thus the normal or pathological cellular phenotype.