Abstract. Antigens specific to pericentral hepatocytes have been studied in adult mouse liver, during fetal development, and in cultured fetal hepatoblasts. Antibody reactive with glutamine synthetase stained all fetal liver cells but almost all cells lost this antigen after birth; only a single layer of pericentral cells retained it in adulthood. In contrast, monoclonal antibodies to major urinary protein (MUP) did not detect the antigen until •3 wk after birth, after which time the cells within 6-10 call diameters of the central veins were positive. Cultured fetal liver cells from embryos at 13 + 1 d of gestation were capable of differentiating in vitro to mimic events that would occur had the cells remained in the animal. About 10-20 % of the explanted cells grew into clusters of hepatocyte-like cells, all of which stained with albumin antibodies. MUP monoclonals were reactive with one-half of the differentiated fetal hepatocytes. Glutamine synthetase was present in all hepatocytes after several days in culture and gradually decreased and remained in only occasional cells, all of which also contained the MUP antigen.These findings suggest that a sequence of gene controis characterizes expression of specific genes in developing liver, and that differentiating fetal hepatoblasts are capable of undergoing similar patterns of gene activity in culture.T rIE adult liver is arranged in acini with the afferent blood supply from the portal vein and the portal artery entering branching vessels at the microscopic level deliver blood to capillary-sized vessels, termed sinusoids, which conduct blood between cords (or plates) of hepatocytes to empty into a central vein. Thus hepatocytes are divided into two zones or regions: periportal (close to the portal afferent circulation) or pericentral (close to the efferent central vein) (51). It is widely accepted that all hepatocytes in rodents and humans contain certain proteins (for example albumin), while other proteins are found at higher levels in cells of one or the other zone (4,8,23,24,32,33,42,55,58,59), perhaps related to the higher nutrient, hormone, and/or oxygen content of blood in periportal compared with the pericentral region. However recent work using immunohistochemical labeling shows a distinct pericentral location for a number of different detoxification enzymes whose regulation is not obviously related to nutrient or oxygen supply (2, 52, 62). These antigens are present either exclusively or predominantly in the 6-10 cell layers immediately surrounding the central vein in adult rodents. In addition, antibodies to glutamine synthetase show this enzyme to be present in rats in a single layer of pericentral cells (22). To supplement our studies on gene expression in mouse hepatocytes, which have emphasized the importance of cell surface contacts in maintaining hepatocyte specific transcription (12), and to begin to examine hepatocytes during fetal development, we prepared a series of mAbs against mouse liver tissue. Many of the first group ofmAbs we obtained rec...