UASt regulatory sequences drive expression of 'Apoliner', a fluorescent sensor for caspase activity. The sensor is comprised of two fluorescent proteins (mRFP1 and EGFP) separated by sequence derived from the Diap1 gene. The Diap1 sequence corresponds to amino acids 1-146 and includes a caspase cleavage site, DQVDGV (this site has been mutated from the original DQVDNN to prevent degradation of the cleaved product by the N-end rule pathway). In addition, a transmembrane domain (Tag:M(mCd8a)) is fused to the N-terminal end of the mRFP1 sequence and a nuclear localization signal (Tag:NLS(SV40-largeT)) is fused to the N-terminal end of the EGFP sequence. In the absence of caspase activity, the transmembrane domain tethers both fluorescent proteins to the membrane. Upon cleavage of the DQVDGV site by active caspase, the EGFP protein is released, and can be targeted to the nucleus via the Tag:NLS(SV40-largeT) signal, while the mRFP1 protein remains tethered at the membrane.

th^{N21G.N22V.Scer\UAS.T:Mmus\Cd8a.T:Disc\RFP-mRFP.T:SV40\nls2.T:Avic\GFP-EGFP} can be used as a reporter of caspase activity.