Expression of the elastin promoter in novel tissue sites in transgenic mouse embryos

We have previously shown in a transgenic mouse line, in which 5.2 kb of the elastin promoter was linked to the reporter enzyme chloramphenicol acetylt ransferase (CAT), that the highest levels of expression were found in embry onic lungs and aorta, while lower levels were detected in other elastin-con taining tissues. Furthermore, in general, expression of the transgene showe d developmental regulation similar to that of the endogenous gene, However, the precise location of cellular expression could not be determined in thi s model. To overcome this limitation, we have developed a similar model, bu t replaced CAT with the reporter enzyme P-galactosidase, Enzyme activity wa s readily detected in the transgenic mouse embryos in expected regions of t issue forming elastic fibers, including the dermis and elastic cartilage. O f considerable interest, however, was the novel finding of expression in sp ecific areas of neuroepithelium of the brain and in the perichondrium surro unding areas destined to form hyaline cartilage in endochondral bone format ion. These latter areas included all the bones of the limbs, the spine and rib cage, It appeared that these segments of elastin expression demarcated the border between the developing cartilage and the surrounding mesenchymal tissue. Elastin promoter expression was also found in developing somites, in the mesenchymal layer of the forming cornea of the eye, in the genital t ubercle and in the epithelium destined to form the olfactory epithelium. Th ese findings indicate that the elastin promoter is activated during embryon ic development in a variety of tissues, suggesting that elastin gene expres sion may play a role in organizing cutaneous, skeletal and neural structure s.