The influence of matrix components on the morphological differentiation of a proliferating hepatocyte line from liver of newborn mice.

The differentiation behaviour of a liver epithelial cell line of the newborn mouse cultured on various matrix components (Thermanox pure, Thermanox coated with ECM, dried collagen type I and type II, wet collagen type I and type III and on floating collagen) was investigated by electron microscopy. Only during the last few days of pregnancy and up to day 9 p.p. could these cells be isolated using a very delicate method. The cells were smaller than differentiated hepatocytes and proliferated spontaneously. They resembled the so-called oval liver cells. On Thermanox pure or Thermanox coated with ECM, dried collagen type I or type II a confluent monolayer developed after about 6 days that consisted of rather flat extended cells which were characterized by short contacts and the absence of any morphological indications of differentiation. On wet collagen the extension area was smaller and the cells were taller. The length of the contact area and the number and size of gap junctions and cell organelles increased. On floating collagen multi-layered aggregates of polygonal cells developed that were characterized by extended cell contacts, bile capillary-like structures and highly developed cell organelles, especially rough endoplasmic reticulum. Since differentiation processes can be demonstrated ultrastructurally only on wet collagen, especially on floating collagen, the chemical composition of the substrate and a specific matrix-cell interaction cannot be the only triggering factor. It is assumed that mechanical properties of the substrate, e.g. plasticity, are involved. The change in the shape of the cell, the prolongation or intensification of the cell contact and the adaptation of the cytoskeleton might play a decisive role in this connection.