DEVELOPMENT OF REICHERTS MEMBRANE IN THE EARLY MOUSE EMBRYO

Although the composition of Reichert's membrane, a thick multilayered basement membrane between the parietal endoderm cells and the trophobl ast cells of rodents, has often been investigated, the site of its pro duction remains a subject of controversial discussion. In particular, the role of the trophoblast cells is unclear. In the present work we e xamined the initial development of Reichert's membrane in the early mo use embryo, using glutaraldehyde fixation with tannic acid. In the ear ly blastocyst the occurrence of a tannic-acid-positive layer located a t the inner surface of the mural trophoblast indicated the onset of ba sement membrane formation by the trophoblast cells. In the peri-implan tation phase, this basement membrane extended into lateral areas of th e inner cell mass separating the newly differentiated ectoderm and end oderm cells from each other. In these lateral regions, where the recen tly formed primitive endoderm cells had been attached to the monolayer ed basement membrane of the mural trophoblast, the membrane began to r eveal the typical multilayered structure of Reichert's membrane. Our f indings indicate that the initial formation of Reichert's membrane beg ins with the formation of a basement membrane of the mural trophoblast cells, followed by an apposition of basement membrane material, proba bly synthesized by primitive endoderm cells, along this primary membra ne.