UASt regulatory sequences drive expression of 'RC3Ai', which is designed to be used as a fluorescent sensor for caspase activity (PMID:23857461). The sensor is initially synthesized as a linear protein composed of an N-terminal intein fragment, a C-terminal portion of the mCherry fluorescent protein, a linker sequence that includes a DEVD caspase cleavage site, an N-terminal portion of the mCherry fluorescent protein, a C-terminal intein fragment and a Tag:MYC tag. The two intein fragments result in self-splicing of the protein, producing a circular molecule that is not fluorescent (the Tag:MYC epitope is removed during the splicing process). In the presence of a caspase that can cleave the DEVD site, the protein is cleaved, which is expected to reconstitute a fluorescent protein, allowing caspase activity to be detected. However, in transgenic flies, RC3Ai forms aggregates in all cell types tested (whether or not apoptosis is occurring) and thus cannot be used as a reporter of caspase activity.