Aggragation of chicken enbryo hepatocytes can be inhibited by Fab' fragments of antibodies prepared against the cells. An aqueous extract of liver cell membranes contained antigens that neutralized the adhesion-blocking properties of the Fab' fragments. This neutralization activity was associated with a polypeptide of Mr68,000 in NaDodSO4; the polypeptide was distinct from serum albumin. Specific antibodies prepared against the 80-fold purified active fraction inhibited liver cell adhesion and immunoprecipitated the 68,000 Mr polypeptide from active fractions as well as from a detergent extract of liver cell membranes. In hepatocyte cultures, Fab' fragments of antibodies against the liver molecule prevented both colony formation and appearance of histotypic patterns. Liver cell adhesion was compared at the cellular and molecular levels to that of embryonic neural retina cells. Antibodies against the cell adhesion molecule from neural tissue inhibited retinal but not liver cell aggregation; conversely, antibodies against the liver polypeptide inhibited liver but not retinal cell aggregation. By means of antibody absorption and immunoprecipitation, it was confirmed that the two cell adhesion molecules are antigenically unrelated.

Gluconeogenesis is a liver-specific pathway which permits the synthesis of phosphorylated sugars from oxaloacetate, pyruvate, amino acids, or trioses. The absolute requirement for glucose or an alternative hexose which characterizes most mammalian cells probably reflects an inablility to perform gluconeogenesis rather than to generate sufficient energy by respiration alone. Cells of diverse histogenetic origins have been tested in glucose-free medium, supplemented with oxaloacetate or with dihydroxyacetone. The only cells able to grow are well-differentiated hepatoma cells which produce the relevant gluconeogenic enzymes: phosphoenolpyruvate carboxykinase, fructose diphosphatase, and triokinase. Reconstruction experiments demonstrate that glucose-free media permit the selective growth of cells producing gluconeogenic enzymes. These media should be useful for analysis of reexpression of differentiated functions in somatic cell hybrids and for the isolation of mutants.

Different endpoints have been used to investigate the occurrence of estrogenic risk along the Po River, particularly its middle section. An in vitro assay based on recombinant yeast could not detect estrogenic activity in bed sediments of the Italian river or in bile samples of five Cyprinid species, with the only exception being one carp (Cyprinus carpio) captured downstream of the River Lambro, a polluted tributary of the middle River Po. Chemical analyses of fish bile and water samples from the same middle section showed diffuse contamination by moderately low levels of estrogenic chemicals (estrone [E1], 17beta-estradiol, estriol [E3], 17alpha-ethinylestradiol, 4-nonylphenol [NP], 4-tert-octylphenol [tOP], 4-n-octylphenol, and bisphenol A) but they were of limited help in understanding the risk present in the downstream area where intersex barbel were previously found. In contrast, the analyses of River Lambro waters showed that this tributary is a source to the middle River Po of all eight estrogens investigated. Analyses of bed sediments and macroinvertebrates from the same area consistently showed at least two levels of contamination, with the downstream stretch showing higher concentrations of natural steroids (E1 and E3) and xenoestrogens (NP and tOP). Accordingly, new histologic examinations undertaken on young barbel (Barbus sp.) showed intersex gonads only in the individuals captured in the downstream stretch, thereby confirming previous results. Present findings confirm the occurrence of disrupting conditions in the middle River Po and provide the first suggestions of cause-effect relationships.

Most of the hybrid clones derived from a cross of Chinese hamster fibroblasts (DON) with rat hepatoma cells (Faza 967) showed preferential loss of rat chromosomes. Two of the hybrid clones retained the rat chromosomes, and both showed extinction of 4 liver-specific enzymes: aldolase B, liver alcohol dehydrogenase, and the inducible enzymes tyrosine aminotransferase and alanine aminotransferase. Subcloning of 1 of these hybrids, which contained 2 sets of hepatoma chromosomes and 1 set of hamster chromosomes, permitted the isolation of some clones which reexpressed 1 or more of the liver-specific enzymes. Liver alcohol dehydrogenase was the most frequently reexpressed enzyme and aldolase B the least. Tyrosine aminotransferase inducibility was reexpressed independently of basal activity, and the enzyme produced by the reexpressing hybrid cells was precipitated by a specific antiserum. No correlation was detected between the presence or absence of the marker chromosomes (large metacentrics) of the hamster parent and the extinction and reexpression of the hepatic enzymes. The results reported confirm and extend to interspecific hybrids the observation of the stable and independent reexpression of tissue-specific enzymes.