A well-defined mechanism governs the maturation of most microRNAs (miRNAs) in animals,
via stepwise cleavage of precursor hairpin transcripts by the Drosha and Dicer RNase III
enzymes. Recently, several alternative miRNA biogenesis pathways were elucidated, the
most prominent of which substitutes Drosha cleavage with splicing. Such short hairpin
introns are known as mirtrons, and their study has uncovered related pathways that combine
splicing with other ribonucleolytic machinery to yield Dicer substrates for miRNA biogenesis …