Transcriptional and posttranscriptional control of connexin mRNAs in periportal and pericentral rat hepatocytes.

Distinct patterns of expression of gap junction, or connexin, mRNAs were observed in periportal vs. pericentral hepatocytes. The two cellular fractions (isolated from rat livers by perfusion) were more than 90% parenchymal, as determined by flow cytometry for a hepatocyte-specific marker. The periportal and pericentral fractions were identifiable due to enrichment in enzymatic activities previously shown to be differentially expressed in the respective regions of liver. Northern blot analyses revealed that mRNA encoding connexin 26 was 2.8 times more abundant in the periportal than in the pericentral cells, while connexin 32 mRNA was equally distributed. Messenger RNA from each fraction was radiolabeled in order to compare the relative abundance of the connexin mRNAs in each fraction. The ratio of connexin 26 to connexin 32 mRNA in the portal fraction was about 0.085, and in the central fraction about 0.038. Connexin 26 mRNA was transcribed, however, at a faster rate than connexin 32 mRNA by nuclei isolated from both cellular fractions. Connexin 26 mRNA was transcribed at 3.9 times the rate in nuclei from the periportal than from the pericentral cells. These data suggest that while the zonation of connexin 26 mRNA synthesis in liver appears to be controlled transcriptionally, posttranscriptional regulatory mechanisms determine the relative abundance of the connexin mRNAs.