UASp regulatory sequences drive expression of the entire osk coding sequence, which is joined to a modified bcd 3'UTR (the putative NRE sequence, a 45bp HpaI-EcoRV fragment has been replaced by a 10bp SpeI linker). An ATG triplet corresponding to the start codon for the osk short isoform has been mutated to CTG, so that the construct only expresses the long isoform of osk.
Oocytes expressing oskM139L.bcd.3'UTR.Scer\UAS.P\T under the control of Scer\GAL4mat.αTub67C.T:Hsim\VP16 show ectopic incorporation of FM4-64 dye at the anterior of the oocyte.