Whole-mount staining of beta galactosidase activity in a heterozygous E15.5 Popdc2-LacZ embryo. After staining the embryo was cleared in benzyl benzoate to visualize internal structures. Differentiated skeletal muscle tissue as well as the umbilical vessels display strong LacZ activity. Expression of the marker gene in the heart and in smooth muscle tissue of the gastrointestinal tract and the coelomic wall are not visible here. See Froese and Brand, Developmental Dynamics 237:762–769, 2008. © 2008 Wiley-Liss, Inc.