MMP-9 (GELATINASE-B) MESSENGER-RNA IS EXPRESSED DURING MOUSE NEUROGENESIS AND MAY BE ASSOCIATED WITH VASCULARIZATION

Expression of MMP-9 mRNA, a type IV collagenase gene product, was foll owed during embryonic development of the mouse brain using in situ hyb ridization. Murine embryos from 7.5 to 15 days after fertilization wer e sectioned and evaluated for MMP-9 expression. During early developme nt, from day 7.5 to day 9, no signal was detected in the cells of the neuroepithelium or in cells of the cephalic mesenchyme of the neural t ube. At day 11, gene expression was localized to the Rathke's pouch an d the germinal zone of the primitive ventricular system. At day 13, bu t most notably at day 15, high levels of MMP-9 were expressed by proge nitor cells in close association with the development of structures, s uch as the hypophysis, the choroid plexus, the ganglion cell layer of the retina and the uveal tract. High MMP-9 mRNA levels were also assoc iated with dense cellular aggregates destined to form the highly vascu lar grey matter of the brain. The presence of MMP-9 mRNA was confirmed using a ribonuclease protection assay. A 105 kDa gelatinase, consiste nt with the expected molecular mass for the murine MMP-9, was detected in embryonic brain extracts by substrate gel electrophoresis. To our knowledge, this is the first report on the localization of MMP-9 in de veloping neural tissues. Our results suggest that MMP-9 expression may have a previously unsuspected role in neural development.