FIGURE 3.

Titration of Cre permits single cell labeling without decreasing signal intensity. Two-photon z-projections of the transfected lobe of the tadpole optic tectum demonstrate that electroporation of 1 μg/μL pCALNL-EGFP plasmid together with increasingly dilute concentrations of pCAG-Cre plasmid results in a decreasing number of labeled tectal cells with little apparent decrease in the brightness of EGFP expression. Animals were imaged (A–E) 2 and (A′–E′) 5 days after electroporation with 1 μg/μL pCALNL-EGFP plus pCAG-Cre concentrations of (A,A′) 100 ng/μL, (B,B′) 10 ng/μL, (C,C′) 1 ng/μL, (D,D′) 0.2 ng/μL, or (E,E′) 0.1 ng/μL. (F,G) Cells continue to mature and develop complex dendritic arbors over this time as can be seen in higher magnification z-series projections. Only the lowest dilution of Cre plasmid produced cells with completely non-overlapping dendritic arbors by day 5, which would be suitable for single-cell reconstruction. Scale bar, (A–E) 50 μm, (F,G) 20 μm.