The GCaMP3 reporter and neomycin resistance cassette replaced the entire coding sequence. The GCaMP consists of, from 5' to 3', a poly-histidine tag (6XHis), 13-residue peptide of myosin light chain kinase (M13), a circularly permutated eGFP interrupted at residue 145, calmodulin (CaM), and a polyA recognition sequence. Mutations resulting in increased brightness (D180Y and V93I), thermal stability (V163A, and S175G) and GFP dimerization prevention (A206K) were introduced. To further stabilize GCaMP and increase fluorescence, four more mutations (R2V, M66K, T116V and N363D) were introduced, resulting in the creation of GCaMP3.