Vegfr2-luc expression during postnatal development. (A) Female Vegfr2-luc mice (n = 3) at the ages of 2, 3, 4, 6, 8, 10, and 15 weeks were imaged as described in “Materials and methods.” Luciferase signal was collected from the dorsal and ventral sides of the mice. The color overlay on the image represents the photons per second emitted from the animal, ranging from 10⁴ to 10⁶ photons/sec, as indicated by the color scales. (B) Quantification of luciferase signal from the whole body with LivingImage software (Xenogen). Luciferase activity is expressed per centimeter squared of animal surface area to correct for differences in animal sizes at different ages. Data are presented as mean ± SE (n = 3).