Transgenic construct that contains a polycistronic gRNA cassette expressed under the control of snRNA:U6:96Ac regulatory sequences. The cassette encodes sgRNAs that target the se, e, cu and f genes, each flanked by tRNA sequence. After the cassette is expressed, the tRNAs should form secondary structures that are recognized by the RNase enzymes P and Z, allowing the release of the sgRNAs.