Resumption of growth of heat inactivated embryonic epiphyses by grafting. Crucial morphogenetic contribution by the extracellular matrix ?

This communication describes a new experimental model for the study of the role of the extracellular matrix (ECM) in morphogenesis. In a preceding paper (Markson et al. 1991) we demonstrated that isolated epiphyses from femora of 6-day-old chick embryos grow during the first days in organ culture almost as well as their intact counterparts. Heating femora for 1 h at 45.2° C caused complete cessation of growth and proteoglycan biosynthesis. When the cut surface of a heat-inactivated (HI) epiphysis was brought into apposition with the cut surface of a live epiphysis and the attached pair placed in organ culture, the HI epiphysis began to grow and reached almost the same size as its live partner. The different possible interpretations of this finding are discussed. When a HI epiphysis of a certain shape (from humerus) is attached to a live epiphysis of a very different shape (from femur) and the attached pair is cultured for 6-7 days, the typical resumption of growth can be observed and the HI epiphysis that doubled or tripled its size retains its original characteristic form. The possibility that the existing infrastructure of the cartilaginous ECM directs the pattern of deposition of newly synthesized ECM by the chondroblasts is discussed, and it is suggested that stretch-activated channels participate in a process by which cells sense the topography of their ECM.