No abstract

Tartrate-resistant acid phosphatase (TRAP) is a secreted product of osteoclasts and a lysosomal hydrolase of some tissue macrophages. To determine whether TRAP expression is rate-limiting in bone resorption, we overexpressed TRAP in transgenic mice by introducing additional copies of the TRAP gene that contained the SV40 enhancer. In multiple independent mouse lines, the transgene gave a copy number-dependent increase in TRAP mRNA levels and TRAP activity in osteoclasts, macrophages, serum, and other sites of normal low-level expression (notably, liver parenchymal cells, kidney mesangial cells, and pancreatic secretory acinar cells).

The defective terminal differentiation of osteoclasts in mice homozygous for the mi allele of the microphthalmia transcription factor (MITF) gene implies that MITF plays a critical role in regulating gene expression during osteoclast ontogeny. To begin addressing the role of this transcription factor in the osteoclast, target genes need to be identified.