A biogenesis step upstream of Microprocessor controls miR-17~92 expression

The precise control of miR-17~92 microRNA (miRNA) is essential for normal development and overexpression of certain miRNAs from this cluster is oncogenic. Here we find the relative expression of the six miRNAs processed from the primary (pri-miR-17~92) transcript is dynamically regulated during embryonic stem cell differentiation. We identify a new miRNA biogenesis intermediate, termed ‘progenitor-miRNA’ (pro-miRNA), that is an efficient substrate for Microprocessor. An autoinhibitory 5’ RNA fragment is cleaved to generate pro-miRNA and selectively license Microprocessor-mediated production of pre-miR-17, -18a, -19a, 20a, and -19b. Using genetic, biochemical, and structural methods we define two complementary cis-regulatory repression domains required for the formation of this inhibitory RNA conformation. We find the endonuclease CPSF3 (CPSF73), and the Spliceosome-associated ISY1 are required for pro-miRNA biogenesis and expression of all miRNAs within the cluster except miR-92. Thus, developmentally regulated generation of pro-miRNA explains the posttranscriptional control of miR-17~92 expression in development.