Fig. 7. Ultrastructural changes in PINCH1-null EBs as seen by Methylene Blue staining. (A-C) (A) Section of a typical wild-type EB with vacuole-containing endodermal cells (en), pseudo-stratified epiblast (ep) and a sharply defined central cavity (cv). (B,C) In PINCH1-null EBs the endoderm is frequently detached (arrow in C) and cells of the ICM and epiblast show different staining intensities (B). (D) Ultrastructural analysis of wild-type EBs revealed cuboidal endodermal cells (en), a thin basement membrane (bm) and an elongated epiblast (ep; D). (E,F) PINCH1-null endodermal and epiblast cells are connected through thin plasma membrane extensions. The epiblast cells are non-polarized, irregular (E) and the endoderm is often detached from the basement membrane (F). Normal endoderm has symmetric tight junctions (arrowheads in G; the inset shows 2 x magnification of the tight junction marked by an arrow). (H) In PINCH1-null endoderm, tight junctions often assemble at the middle or basal portion of cell-cell contacts. Sometimes asymmetric tight junctions form in PINCH1-null endoderm with one lateral plasma membrane of a cell not in direct contact with that of another (inset).