Figure 1.

Fetal development of intrahepatic bile duct epithelium is a highly coordinated process involving several different cell types. Initially, the hepatoblasts (HB) aligning along the nascent portal tract centered around the portal vein (PV) branches are primed to gain biliary-like characteristics and transdifferentiate into single layer ductal plate (slDP, red cells), the primordial structure of the bile duct, that further progresses to double layer ductal plate (dlDP). In normal conditions, dlDP migrate into the portal mesenchyme to become incorporated as fully differentiated bile ducts (BD). When this maturation process is perturbed, as by genetic defects, DPM develop at the margins of the portal tract, and are often associated with the nearby deposition of fibrotic tissue.