SCANNING ELECTRON MICROSCOPICAL AND HISTOCHEMICAL-STUDY OF THE STRUCTURE AND FUNCTION OF BASEMENT-MEMBRANES IN THE EARLY CHICK-EMBRYO

A regional pattern exists in the structure and chemical composition of the basement membrane associated with the chick embryo ectoderm during and after gastrulation. The basement membrane consists of a thin amorphous sheet, separable from the associated cells by treatment with Triton X-100. A meshwork of fibrils is associated with the outer surface of this sheet, i.e. with the side facing away from the ectoderm cells. No obvious regional differences were seen in the appearance of the sheetlike component of the membrane. Four well marked zones could be demonstrated in the arrangement of the fibrils in all embryos examined between stage 3 and stage 6. The pattern was gradually lost after the formation of somites.