Basement membrane chondroitin sulfate proteoglycan and vascularization of the developing mammalian limb bud

We used immunocytochemistry to study the basement membrane-chondroitin sulf ate proteoglycan (BM-CSPC) distribution in mammalian limb bud and its relat ionship to and possible role in limb development. Anti-BM-CSPG immunostaini ng was examined in the developing limb buds of 24 Sprague-Dawley rats at em bryonic days 12 to 14 and 19. BM-CSPC immunostaining was present in 3 regio ns. The first region was located peripherally in the limb bud ectodermal ba sement membrane (BM) that separates ectoderm from mesoderm and was present at all embryonic stages examined. The second region was in the mesenchymal extracellular matrix independent of the vascular system. This staining patt ern was diffuse, granular, and often homogeneous, except for clustering adj acent to developing vessels, and was observed distally in the limb bud. In the mesenchymal extracellular matrix adjacent to the distal BM this stainin g pattern formed fibrils that were perpendicular and connected to the limb bud BM and extended into the underlying mesenchyme. The third region was lo calized to the BM of developing blood vessels of the limb bud. Blood vessel staining allowed analysis of limb bud vessel formation. The early developi ng blood vessels at the proximal limb bud were organized differently from t hose located distally. Large central vessels were present proximally, where as a rich plexus of smaller vascular channels was present at the distal mar gin. A subectodermal avascular zone was observed at the margin of the limb bud, except beneath the apical ectodermal ridge where immunostained blood v essels extended from the distal vascular plexus toward the apical ectoderma l ridge. The formation of central larger vessels occurs proximally, whereas formation of peripheral smaller vessels seems to lake place locally and di stally under the influence of the apical ectodermal ridge. BM-CSPC plays an important role in blood vessel formation and mammalian limb bud developmen t. Copyright (C) 2000 by the American Society for Surgery of the Hand.