UAS regulatory sequences drive expression of a dicistronic transcript that encodes two open reading frames separated by a 2A linker (this results in separate translation of each protein). The first ORF encodes the G-CEPIA1 Ca[2+] indicator that is tagged with Tag:TM(hPDGFRB) (this targets the G-CEPIA1 sensor to the outer leaflet of the plasma membrane). The second ORF consists of the Ca[2+]-insensitive TagRFP protein fused to Tag:TM(hPDGFRB); expression of this second protein allows ratiometric imaging.