Figure 4.

Protein expression in the "ductal plate" stage at 5 weeks + 6 days post conception. (A) The graphical interpretation of the "ductal plate" stage illustrates how the partly bi-layered ductal plate is surrounded by primitive hepatocytes. (B) CK7 could not be detected at this time of development. (C) CK19, (D) EpCAM, and (E) HepPar1 were expressed by both primitive hepatocytes and ductal plate cells, whereas strongest SOX9 (F) expression localized to the latter. Parts of the parenchymal (outer) ductal plate layer displayed little or no immunoreactivity for EpCAM (d - arrow) or SOX9 (f, arrow), while parts of the mesenchymal (inner) ductal plate layer displayed little immunoreactivity for HepPar1 (e, arrow). Laminin (G) and nestin (H) were predominantly present throughout the portal mesenchyma and along the sinusoids. AQP1 (I) stained the venous endothelia. Upper case letters x10, lower case letters x63. Scale bar: 100 μm (for all photos marked with upper cases).