New RNA-Seq methods give us the ability to comprehensively and accurately assess the levels of the entire repertoire of miRNAs (including all sequence variants) in a given sample.
Researchers at the Institute for Systems Biology have conducted a comprehensive survey of microRNA isomiRs from human and mouse samples using next generation sequencing platforms and constructed a database that catalogs all microRNA isomiRs.
Their results suggest that the process of generating this isomiR spectrum might not be random and that heterogeneity at the ends of miRNA affects the consistency and accuracy of microRNA level measurement.
The isomiR database is available at http://galas.systemsbiology.net/cgi-bin/isomir/find.pl
The database enables users to determine the most abundant sequence and the degree of heterogeneity for each individual microRNA species. This information will be useful both to better understand the functions of isomiRs and to improve probe or primer design for microRNA detection and measurement.
Lee LW, Zhang S, Etheridge A, Ma L, Martin D, Galas D, Wang K. (2010) Complexity of the microRNA repertoire revealed by next-generation sequencing. RNA 16(11), 2170-80. [abstract]