AN ULTRASTRUCTURAL, MICROANALYTICAL, AND SPECTROSCOPIC STUDY OF BONE FROM A TRANSGENIC MOUSE WITH A COL1.A1 PRO-ALPHA-1 MUTATION

A line of transgenic mice have been investigated that expressed modera te levels of an internally deleted human gene for the pro alpha(I) cha in of type I procollagen. These mice expressed the gene at approximate ly 50% that of the endogenous gene. The gene construct was modeled aft er a sporadic in-frame deletion of the human gene that produced a leth al variant of osteogenesis imperfecta by causing biosynthesis of short ened pro alpha(I) chains. Periera et al. (1993) reported extensive fra cturing in these mice with femurs that were shorter in length and bone that had decreased ash weight, mineral, and collagen content. These w orkers demonstrated an increased brittleness in bone using biomechanic al measurements. The functional consequences of these mutant genes wer e examined in both transgenic and in normal littermate mice to determi ne if a valid model at the ultrastructural and analytical level had be en produced for OI. X-ray microanalysis of bone mineral demonstrated a significantly lower calcium-to-phosphorus (Ca/P) molar ratio in trans genic mouse bone than in normal littermates; this was a feature of hum an OI bone. Fourier transform infrared spectroscopy confirmed that the mineral present was apatitic in nature despite the lower Ca/P molar r atio. Alizarin red skeletal staining showed the presence of multiple f racture calluses on the ribs and on the long bones of some of the tran sgenic mice, this was not seen on normal littermates. No light microsc opic differences were observed between normal and transgenic mice; how ever, many ultrastructural correlates with human OI were observed in t he transmission electron microscope. Anomalous fibrils associated with type I collagen, and an amorphous calcified material was observed lin ing the cartilage, extending beyond the lamina limitans in young trans genic mice.