CELLULAR-ORIGIN OF THE BASEMENT-MEMBRANE IN EMBRYONIC CHICKEN QUAIL CHIMERAS

The cellular origin of the components of the basal lamina of an epithe lium, the chicken epiblast, has been investigated in a model system re sulting from the transplantation of metabolically labeled quail hypobl ast (an epithelium without basal lamina), associated or not with indiv idual mesoblast cells, into an unlabeled chicken blastoderm deprived o f its own hypoblast. The ability to discriminate chicken from quail ce lls after nuclear staining, combined with autoradiographic labeling of the basal lamina components, made it possible to determine the origin of the cells and labeled compounds in tissue sections of the chimeras . The transplantation of H-3-glucosamine or H-3-fucose-labeled quail h ypoblast into a chicken host embryo, and subsequent culture of the chi meric embryo for 5 h, led to the transfer of labeled macromolecules fr om the quail graft to the chicken basal lamina. Pre-treatment of secti ons with several glycosaminoglycan-degrading enzymes with different su bstrate specificities suggested that the H-3-glucosamine-labeled compo unds that are deposited in the basal lamina are glycoproteins and/or h eparan sulfate proteoglycan. However, in view of our current knowledge of the cellular origin of the latter compound, this molecule probably originates from the epithelium itself. Transfer of H-3-proline and H- 3-hydroxyproline-containing molecules (mainly collagens) from the graf t to the host basal lamina was not observed. Chasing the labeled compo unds with unlabeled precursor during culture of the chimeras did not i nfluence the final autoradiographic pattern. It is concluded that the basal lamina of the epiblast has a dual epithelial origin, resulting f rom the interaction of epiblast-derived materials and non-collagenous glycoproteins synthesized by the hypoblast. Evidence supporting the ca se of a non-epithelial, mesoblastic origin of non-collagenous glycopro teins was not found. An extensive review of literature on the epitheli al vs non-epithelial origin of basement membrane components, mainly in mammalian species, is also provided.