REGIONAL DIFFERENCES OF DURA OSTEOINDUCTION - SQUAMOUS DURA INDUCES OSTEOGENESIS, SUTURAL DURA INDUCES CHONDROGENESIS AND OSTEOGENESIS

Dura plays an important role in calvarial morphogenesis. However, prec isely what that role is remains unclear. We present here in vivo evide nce that dura without other central nervous system components induces both chondrogenesis and osteogenesis. The mechanism is, at least in pa rt, by proximate tissue interaction. The objectives of this experiment were to answer the following: (1) Can dura actually induce osteogenes is without the influence of the underlying brain? (2) What are the req uirements of this dura-induced heterotopic osteogenesis? (3) What are the differences between dura underlying sutures and dura underlying th e squamous portions of the cranial bones? Dura underlying the metopic, sagittal, and lambdoidal sutures and dura underlying tile flat portio ns of frontal and parietal bones were obtained from neonatal Lewis rat s and transplanted into the posterior thoraces of adult Lewis recipien ts. In group I, dura underlying the metopic, sagittal, and lambdoidal sutures (n = 20) and dura underlying the flat portions of frontal and parietal bones (n = 20) were transplanted individually into separate e pitheliomesenchymal pockets. Group II animals had dura underlying the metopic, sagittal, and lambdoidal sutures (n = 10) and dura underlying the flat portions of frontal and parietal hones (n = 10) transplanted individually into surgically created mesenchymal pockets by placing t he dura grafts between panniculus carnosus and latissimus dorsi muscle s. The animals were sacrificed tit 2-week in tervals. Light microscopy , special histochemical analysis, immunohistochemistry, and electron m icroscopy were performed. Bone formation was seen in 15 of the 18 anim als (83 percent) in group I. No bone or cartilage formation was seen i n group II, Chondrogenesis was seen in LL animals receiving dura under lying tile metopic, sagittal, and lambdoidal sutures in group I. Cellu lar hyper proliferation was seen at 2 weeks when dura was transplanted close to the hair follicles. These cells had a high nucleus-to-cytopl asm ratio and were positive for transforming growth factor beta. This hyperproliferation was followed by production and accumulation of Alci an blue-positive extracellular matrix that resisted digestion by hyalu ronidase. Cellularly active cartilage was seen at Ci weeks. There was no chondrogenesis in animals receiving dura underlying the flat portio ns of frontal and parietal bones in group. Electron microscopy demonst rated tile presence of proteoglycan-like ground substance and type II collagen in the inner layer of sutural dura and the predominance of de nse type I collagen in tile squamous dura and the external layer of ti le sutural dura. The important findings of this experiment are that (1 ) heterotopically transplanted neonatal dura can induce osteogenesis, (2) this heterotopic osteoinduction by dura requires epitheliomes-ench ymal interaction, and (?I) separating dura into sutural dura and squam ous dura, chondrogenesis occasionally occurred in addition to osteogen esis with the former, while only membranous ossification occurred with the latter, indicating intrinsic differences within the dura mater. T his dural heterogeneity is supported by direct ultra structural data.