CRANIAL SUTURES REQUIRE TISSUE INTERACTIONS WITH DURA-MATER TO RESISTOSSEOUS OBLITERATION IN-VITRO

A chemically defined serum-free medium,,which supports the development of bones and fibrous tissues of rat calvaria from nonmineralized mese nchymal precursor tissues, was employed to investigate tissue interact ions between the dura mater and overlying tissues. Fetal calvarial rud iments from stages prior to bone and suture morphogenesis (fetal days 19 and 20) and neonatal calvarial rudiments with formed sutures (day 1 ) were cultured with and without associated dura mater. Removal of cal varia for in vitro culture allowed the examination of suture morphogen esis in the absence of tensional forces exerted on the sutures via fib er tracts in the dura mater originating in the cranial base, Ossificat ion of frontal and parietal bones proceeded in a fashion comparable to development in vivo, but the cranial (coronal) sutures-primary sites for subsequent skull growth-were obliterated by osseous tissue union i n the absence of dura mater. Bony fusion did not occur when rudiments were cocultured with dura mater on the opposite sides of 0.45 mu m pol ycarbonate transwell filters, suggesting that the influence of dura ma ter on sutural obliteration was mediated by soluble factors rather tha n cell-cell or cell-matrix interactions. These results indicate that c ell signaling mechanisms rather than biomechanical tensional forces ar e required for morphogenesis of the calvaria.