Specialization of the Drosophila nuclear export family protein Nxf3 for piRNA precursor export
RNA nuclear export is a tightly regulated process. A new study in Genes&Development shows that some transcripts in the Drosophila germline are exported via a novel mechanism that by-passes the canonical steps required for mRNA export. This unusual route is centred on Nxf3, a paralog of the canonical mRNA exportin Nxf1, and Bootlegger and ensures that these transcripts escape nuclear RNA decay mechanisms and reach the cytosol, where they are processed into piRNAs.
These special transcripts arise from heterochromatic "dark" areas of the genome and leave the nucleus under the radar of the canonical mRNA export machinery. I imagine Nxf3 and Bootlegger like smugglers transporting these transcripts under cover of darkness. The illustration was inspired by the beautiful confocal microscopy images of nurse cell nuclei by E. Kneuss (see some examples in Figure 1).
Kneuss E, Munafò M, Eastwood EL, Deumer US, Preall JB, Hannon GJ, Czech B. Specialization of the Drosophila nuclear export family protein Nxf3 for piRNA precursor export. Genes Dev. 2019 Sep 1;33(17-18):1208-1220. doi: 10.1101/gad.328690.119. Epub 2019 Aug 15. PMID: 31416967; PMCID: PMC6719614.