Characterization of the compact bicistronic microRNA precursor, miR-1/miR-133, expressed specifically in Ciona muscle tissues

► Ciona miR-1/miR-133 is only 350 nt long and located in conserved genomic location. ► miR-1/miR-133 precursor is expressed specifically in embryonic and adult muscles. ► Mature miR-1 and miR-133 differentially accumulate in adult body wall and heart. ► Muscle specific expression is driven by the 850-bp upstream regulatory sequence.