Introduction

The miRBase database (formerly entitled the microRNA Registry) is the primary online repository for microRNA (miRNA) sequences and annotation (Griffiths-Jones, 2004; Griffiths-Jones et al., 2006). When laboratories first began to clone and sequence increasing numbers of miRNAs (Lagos-Quintana et al., 2002) it became apparent that a single resource for the naming, annotation and dissemination of published miRNAs was urgently required. With no predefined nomenclature or central repository for miRNA sequences there was a distinct danger that these sequences would appear in journals with inconsistent names. Furthermore, if miRNAs were independently identified by multiple laboratories and had multiple ambiguous identifiers this could hamper subsequent analysis. Previously, the RFAM project (Griffiths-Jones et al., 2003) at the Wellcome Trust Sanger Institute had been cataloging and identifying RNAs and their evolutionary relationships and hence already had much of the expertise required. A number of laboratories involved in miRNA research discussed these issues and published a collaborative document detailing the agreed nomenclature for miRNAs and announcing the miRNA registry as their main repository (Ambros et al., 2003).

Recently the resource has expanded to include miRNA annotations and automatically predicted targets for animal miRNAs and has been renamed miRBase (Griffiths-Jones et al., 2006). This resource currently attracts a very large number of visitors and registered over 1.5 million page hits in July 2006 alone, illustrating the growing scientific interest in these important regulatory molecules.