Defective liver formation and liver cell apoptosis in mice lacking the stress signaling kinase SEK1/MKK4

The stress signaling kinase SEK1/MKK4 is a direct activator of stress-activated protein kinases (SAPKs; also called Jun-N-terminal kinases, JNKs) in response to a variety of cellular stresses, such as changes in osmolarity, metabolic poisons, DNA damage, heat shock or inflammatory cytokines. We have disrupted the sek1 gene in mice using homologous recombination. Sek1(−/−)embryos display severe anemia and die between embryonic day 10.5 (E10.5) and E12.5. Haematopoiesis from yolk sac precursors and vasculogenesis are normal in sek1(−/−)embryos. However, hepatogenesis and liver formation were severely impaired in the mutant embryos and E11.5 and E12.5 sek1(−/−)embryos had greatly reduced numbers of parenchymal hepatocytes. Whereas formation of the primordial liver from the visceral endoderm appeared normal, sek1(−/−) liver cells underwent massive apoptosis. These results provide the first genetic link between stress-responsive kinases and organogenesis in mammals and indicate that SEK1 provides a crucial and specific survival signal for hepatocytes.

Stem Cells and Rat Liver Carcinogenesis: Contributions of Confocal and Electron Microscopy

Microscopic analysis in combination with cytochemistry and immunocytochemistry has revealed the presence of four cell types not previously described in the portal area and parenchyma of the liver from an experimental rodent hepatocarcinogenic rat model. Within the intrahepatic bile ductules, which proliferate after administration of chemical carcinogens and partial hepatectomy, small, undifferentiated nonpolarized, nonepithelial cells with a blast-like phenotype and polarized epithelial cells different from the polarized epithelial cells that typically line the walls of the bile ductules were found. In the connective tissue stroma surrounding the bile ductules, nonpolarized epithelial cells with hepatocyte phenotype were found. In the parenchyma, subpopulations of bile ductule epithelial cells that established ATPase-positive bile canalicular structures, including the formation of desmosomes and tight junctions, with parenchymal hepatocytes within the hepatic lobule were found. These observations raise the following questions in this model. Are there undifferentiated progenitor cells with stem cell-like properties within bile ductules? What are the interrelations of the newly described cell types with each other, with parenchymal hepatocytes, with preneoplastic nodules, and with hepatomas? Do the heterogeneous cell types within the bile ductules, in the surrounding connective tissue, and within the hepatic cords represent intermediate stages of single or multiple cell lineage pathways leading to hepatocyte differentiation, liver regeneration, and/or preneoplastic nodule formation?

STEM Cells and Liver Carcinogenesis: Contributions of Light, Confocal and Electron Microscopy

Three cell types not previously described were revealed by the application of several microscopic procedures in combination with cytochemistry and irnmunocytochemistry in the livers of rats treated according to the Solt et al carcinogenesis protocol. This protocol consists of the administration of an initiating carcinogen (diethynitrosamine), a mitoinhibitory carcinogen, (acethylaminofluorene) and a growth stimulus (partial hepatectomy) (1). Two of the cell types were found in intrahepatic bile ductules and one within the connective tissue stroma surrounding the ductules. These findings have implications for understanding the cell lineage pathways that operate in an experimental rodent hepatocarcinogenesis system in which hepatocyte regeneration is inhibited and in which preneoplastic nodules and hepatomas develop. Our previous studies have determined some of the enzymatic, antigenic and structural properties of these cell types and their interrelations to each other, to parenchymal hepatocytes and to preneoplastic nodules (2).Proliferation of bile ductule cells occurs early (24-48 hrs) after the partial hepatectomy step of the protocol with extensive branching of the ductules into the hepatic parenchyma.

Expression of the class I alcohol dehydrogenase gene in developing rat fetuses.

Class I alcohol dehydrogenase (ADH) is the principal enzyme responsible for ethanol oxidation in mammals. Although primarily regarded as an enzyme that functions in the adult, Class I ADH has been reported to be present in fetal tissues. By in situ hybridization, we demonstrated the tissue localization of the Class I ADH transcript in developing rat fetuses between Days 15 (E15) and 18 (E18) of gestation. Abundant transcripts were present in epidermis, lung, and urinary bladder. In these tissues, the messages were localized primarily to the superficial layer of the epithelium and increased with development. The liver exhibited significant signals only in the E18 fetus, when parenchymal hepatocytes first appeared. The E15 and E16 small intestines, with their epithelium arranged in a stratified fashion, displayed signals in the submucosal mesenchymal layer. By E17, a rearrangement of the intestinal epithelium into an almost monolayer configuration was observed. This change was associated with a redistribution of the ADH transcript to the surface of the epithelium. Further relocation of the messages was noted in the adult small intestine, in which they became concentrated in the base of the crypt. These findings indicate that expression of the rat class I ADH gene follows a dynamic course in specific epithelial tissues during fetal development. In addition, the apparent superficial localization of the ADH message in most of these tissues suggests that ADH functions in metabolizing either endogenously or exogenously derived alcohol substrates present in the fetal environment.