Development of Reichert's 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 trophoblast cells of rodents, has often been investigated, the site of its production remains a subject of controversial discussion. In particular, the role of the trophoblast cells is unclear. In the present work we examined the initial development of Reichert's membrane in the early mouse embryo, using glutaraldehyde fixation with tannic acid. In the early blastocyst the occurrence of a tannic-acid-positive layer located at the inner surface of the mural trophoblast indicated the onset of basement membrane formation by the trophoblast cells. In the peri-implantation phase, this basement membrane extended into lateral areas of the inner cell mass separating the newly differentiated ectoderm and endoderm cells from each other. In these lateral regions, where the recently formed primitive endoderm cells had been attached to the monolayered basement membrane of the mural trophoblast cells, followed by an apposition of basement membrane material, probably synthesized by primitive endoderm cells, along this primary membrane.