The Conserved RNA Exonuclease Rexo5 Is Required for 3′ End Maturation of 28S rRNA, 5S rRNA, and snoRNAs

Non-coding RNA biogenesis in higher eukaryotes has not been fully characterized. Here, we studied the Drosophila melanogaster Rexo5 (CG8368) protein, a metazoan-specific member of the DEDDh 3'-5' single-stranded RNA exonucleases, by genetic, biochemical, and RNA-sequencing approaches. Rexo5 is required for small nucleolar RNA (snoRNA) and rRNA biogenesis and is essential in D. melanogaster. Loss-of-function mutants accumulate improperly 3' end-trimmed 28S rRNA, 5S rRNA, and snoRNA precursors in vivo. Rexo5 is ubiquitously expressed at low levels in somatic metazoan cells but extremely elevated in male and female germ cells. Loss of Rexo5 leads to increased nucleolar size, genomic instability, defective ribosome subunit export, and larval death. Loss of germline expression compromises gonadal growth and meiotic entry during germline development.