UAS regulatory sequences drive expression of the "TN-XL" protein to which the Mmus\Cd8a transmembrane domain has been added at the N-terminal end and a short Glycin-linker followed by six amino acids known to bind the PDZ domain of mint has been added at the C-terminal end. The aim was to produce a calcium ion sensor that would be targeted to axons when expressed using an appropriate GAL4 driver. However, axonal targeting of the protein is not seen when it is expressed in neurons of transgenic flies and the calcium sensitivity of the reporter is essentially lost. Instead, at low to medium expression levels, the protein highlights the somata efficiently. The protein seems to be trapped in the endoplasmic reticulum.