Effects of fetal calf serum and disruption of cadherin function on the formation of bile canaliculi between hepatocytes.

The polarization of hepatocytes to form a connected network of bile canaliculi (BC) is necessary for the function of the liver. Hepatocyte polarization may be controlled by soluble factors and/or physical interactions between cells. Monolayer cultures of embryonic chicken hepatocytes in DMEM supplemented with ornithine, dexamethasone, and insulin express BC-specific antigens for at least 7 days. However, BC-specific antigen expression is lost within 3 days of culture initiation in DMEM containing 10% fetal calf serum. The dedifferentiating effects of fetal calf serum (FCS) can be reversed. Furthermore, cultures in medium containing ornithine, dexamethasone, insulin, and 10% FCS appear identical to cultures grown in 10% FCS alone. Thus FCS contains a soluble inhibitor of hepatocyte polarization. Aggregate cultures grown in suspension maintain hepatocyte polarization for 10-12 days. This may be due to the increased cell-cell contact between hepatocytes in aggregate culture or to more normal contact with the extracellular matrix. We have evaluated the role of cadherin-mediated interactions on hepatocyte polarization. Anti-E-cadherin Fab' fragments disrupted the formation of long networks of BC in monolayer cultures but did not stop polarized expression of BC-specific antigens. The BC antigens in anti-E-cadherin-treated cells were concentrated in small areas between cells and were present at lower levels uniformly on the cell surface. These results indicate that E-cadherin is required for the formation of extended BC networks, but that other factors are responsible for maintaining the synthesis and localization of BC-specific antigens.