Figure 4.

ß-galactosidase assay of Cre activity of the lentivector after targeted injection into a Cre reporter mouse, Rosa26R. (A) Graphic depictions of targeted lentivector injection into the Rosa26R Cre reporter mouse (left), and of the modified Rosa26 locus carrying the floxed PGK neo cassette that carries four polyadenylation sequences (4×pA) to prevent lacZ expression in the absence of the recombinase activity (right). Only after recombination between loxP elements via Cre activity does lacZ expression occur. (B) ßGal activity in the C2 barrel of a tangential section at low magnification from the brain of an injected animal (left), and schematic drawing of this somatosensory barrel field and injection site (right) are shown. (C) At higher magnification, the GFP signal (left) is aligned with the ßGal signal (right). The black hole in the fluorescence image (left) and the aligned white hole (right) is not due to damage from the injection, but to the location of a normal blood vessel.