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 y, cv, v, f and car genes, which each separated by tRNA:His-GTG-1-4 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.