Antibodies as probes of cellular differentiation and cytoskeletal organization in the mouse blastocyst

Abstract

Indirect immunofluorescence microscopy has been used to detect cytoskeletal proteins, which allow a distinction between the two cell types present in the mouse blastocyst: i.e. the cells of the inner cell mass (ICM) and the outer trophoblastic cells. Antibodies against three classes of intermediate-sized filaments (cytokeratins, desmin and vimentin), as well as antibodies against actin and tubulin were studied. Antibodies against prekeratin stain the outer trophoblastic cells but not the ICM in agreement with the findings on adult tissues that cytokeratins are a marker for various epithelial cells. Interestingly, vimentin filaments typical of mesenchymal cells as well as of cells growing in culture seem to be absent in both cell types of the blastocyst. Thus, the cytokeratins of the trophoblastic cells seem to be the first intermediate-sized filaments expressed in embryogenesis. Antibodies to tubulin and actin show that microtubules and microfilaments are ubiquitous structures, although microfilaments have a noticeably different organization in the two cell types. In addition, since early embryogenic multipotential cells show close similarities to teratocarcinomic cells, a comparison is made between the cells of the blastocyst, embryonal carcinoma cells (EC cells) and an epithelial endodermal cell line (PYS2 cells) derived from EC cells. EC cells display vimentin filaments whereas PYS2 cells show both vimentin and cytokeratin filaments. The results emphasize the usefulness of antibodies specific for different classes of intermediate filaments in further embryological studies, and suggest that cells of the blastocyst and EC cells differ with respect to vimentin filaments.