Transgene expression at E13.5. Parasagittal sections of E13.5 transgenic (A, bright field and B, dark field) or wild-type (C, dark field) animals, hybridized with CAT antisense probe. With the exception of the brain, specific signals were detected in the vasculature of all the embryo. Probe did not show any reactivity in nontransgenic mice. Scale bar represents 15 μm; b, brain; c, choroid plexus; d, duodenum; h, heart; k, kidney; li, liver; lm, limb; lu, lung; u, umbilic.