The cell-surface expression of the cell adhesion molecule cellCAM 105 in rat fetal tissues and regenerating liver

In the present investigation we have used a sensitive immunohistochemical technique to study the appearance and cell-surface distribution of cellCAM 105 in rat fetal tissues and in regenerating liver. CellCAM 105 is an integral membrane glycoprotein that is involved in cell-cell adhesion of mature rat hepatocytes in vitro. In 12-day-old rat fetuses no cellCAM 105 was detected. CellCAM 105 then appeared on Day 13 in megakaryocytes of the fetal liver, on Day 16 in the liver parenchyme, and on Day 17 in the epithelial cells of the proximal kidney tubules and of the small intestinal mucosa. In the liver parenchyme cellCAM 105 first appeared in immature bile canaliculi. During Days 19-21 a significant staining also occurred on the contiguous sides of the hepatocytes, which at that time became closely associated when the blood-forming cells disappeared. This surface staining then gradually disappeared and 2-3 weeks after birth cellCAM 105 was expressed in the bile canalicular area which is typical of mature hepatocytes. In regenerating liver the amount of cellCAM 105 decreases to a minimum 2-3 days post-hepatectomy, then increases and reaches the normal concentration 10-15 days post-hepatectomy [Odin and Obrink (1986) Exp. Cell Res. 164, 103-114]. The cell-surface distribution of cellCAM 105 also changed, and on Days 3-5 post-hepatectomy it appeared on all faces of the hepatocytes which then were closely associated without obvious sinusoids in between. This staining pattern then slowly changed toward the normal pattern of mature liver, which appeared about 15 days post-hepatectomy. A theoretical analysis of the mode of hepatocyte cell division during liver regeneration suggested that the surface of the postmitotic hepatocytes should become unpolarized with respect to macromolecular composition. This is in agreement with the observed surface distribution of cellCAM 105. The results support the hypothesis that cell-surface interactions mediated by cellCAM 105 might contribute to the regular organization of hepatocytes in the normal, mature liver plates.