The demonstration of synthesis of basement membrane

by parietal yolk sac epithelium (14), alid the observation that t his epithelial basement membrane material (EBM) is antigenically (13, 15) and chemically (11) unrelated to connective tissues, but is associated with almost all epi thelia in the mouse (10), are compatible with the con cept that basement membranes between epithelia and stroma are synthesized by the epithelial cells. Most of the data on the epithelial origin of basement membranes were obtained through manipulation of a parietal yolk sac carcinoma (13-45). Since neoplastic cells are often easier to manipulate than normal ones, a study has been made of a group of murine neoplasms to determine their relationship to EBM. In the course of the study reported here, it was observed that tumors originating from epithelia which are normally associ ated with EB1\I contain EB1\l; moreover, 2 of these tumors synthesized EBM in tissue culture in the absence of eon nective tissue elements.