We have derived a cell line, RE1, from a pre-implantation rat blastocyst, r
esembling morphologically; the L2 cell line from a parietal yolk sac carcin
oma of the rat, as well as parietal endoderm cell lines of the mouse. The s
ub-cellular organization and epithelial characteristics of RE1 cells are de
scribed. The cells express cytokeratins of simple epithelia, and vimentin;
and demonstrate synthesis of proteins of the extracellular matrix, such as
laminin and collagen IV. Extensive Reichert's-like basement membrane is for
med by RE1 cells when grown in suspension as aggregates. Cells have a micro
villous surface morphology and abundant, rough endoplasmic reticulum which
is swollen with apparent, secretory material. These morphological and cytoc
hemical features are characteristic of parietal endoderm cells in vivo, and
the RE1. cell line is deduced to be rat parietal endoderm. In addition, RE
1 cells were examined for expression of stage-specific embryonic antigens:
cells reacted with antibody against SSEA-1/TEC-1 and EMA-1, constituting th
e first observation of parietal endoderm cells expressing the respective ep
itopes. RE1-cell monolayers did not generate transepithelial resistances or
potential differences in vitro, consistent with their formation of leaky e
pithelia. Our observations on RE1-cell morphology and ultrastructure are co
nsistent with the occurrence of epithelial-mesenchyme transitions in cultur
e. (C) 2001 Harcourt Publishers Ltd.