Developmental Expression of the Endogenous TIMP Gene and a TIMP-lacZ Fusion Gene in Transgenic Mice

We determined the expression pattern of the tissue inhibitor of metalloproteinase (TIMP) in the development of the mouse embryo using in situ hybridization and transgenesis. Localized TIMP RNA was first detected at 13.5 days post conceptus (p.c.) in tissues undergoing osteogenesis, such as the mandible, ribs, and calvaria. As development proceeded, TIMP RNA could be detected at additional sites, including the tooth buds, vertebrae, and long bones. To define the sequences regulating TIMP expression, we generated transgenic mice that expressed the Escherichia coli beta-galactosidase gene under control of a 5' region of the mouse TIMP gene containing -2158 to -58 bp upstream of the initiator ATG. By use of an in situ assay for beta-galactosidase activity, the TIMP-lacZ fusion gene product was localized to tissues that also expressed the endogenous TIMP gene, such as the mandible, calvaria, and vertebrae. The localization of TIMP to regions of intramembranous and endochondral bone is similar to that previously reported for TGF-beta, a growth modulator believed to be involved in regulation of extracellular matrix (ECM) formation. Thus, the expression of TIMP in these regions is consistent with it playing a role in ECM deposition and turnover in development.