UASt regulatory sequences drive expression of the N-terminal of nSyb (amplified using PCR primers: 5' n-Syb (ACAGCCGAATTCGCTGAGGC) and 3' n-Syb-BsrB1 (CCAATTAGATCTCCGCTCACGCCGCCGTGATCGCC)) fused at its C-terminal to pHluorinSE (a pH-sensitive fluorescent protein).