Hepatocytes play a pivotal role in both the synthesis and degradation of numerous endogenous biomolecules, thus maintaining metabolic homeostasis, as well as in the conversion and detoxification of xenobiotic compounds. Based on the location of the blood vessels, the terminal branches of the portal and the hepatic (central) veins and on the direction of the blood flow, hepatocytes of each liver lobule can be divided into two subpopulations, an upstream 'periportal' and a downstream 'perivenous' (pericentral) population. Zonal-specific differences in the metabolic capacities of many enzymes or other proteins, and -to a lesser extent ) of their corresponding messenger RNAs, have been subject to extensive studies throughout the last decades.Many enzymes of intermediary metabolism are not distributed uniformly throughout the liver, but are preferentially expressed in either the periportal or the perivenous hepatocyte subpopulation [1][2][3]. Hence, hepatocytes located in either of the two regions have different, often complementary, functions. Whereas, for example, glycolysis is exclusively active in perivenous hepatocytes, key enzymes of gluconeogenesis, the antagonist pathway, are preferentially expressed in periportal hepatocytes [1]. Zonal-specific expression has also been established for enzymes of amino acid and ammonia metabolism, showing, for example, a higher activity of the urea cycle in periportal cells compared to perivenous hepatocytes [3], whereas glutamine synthesis is exclusively active in the perivenous Hepatocytes located in the periportal and perivenous zones of the liver lobule show remarkable differences in the levels and activities of various enzymes and other proteins. To analyze global gene expression patterns of periportal and perivenous hepatocytes, enriched populations of the two cell types were isolated by combined collagenase ⁄ digitonin perfusion from mouse liver and used for microarray analysis. In total, 198 genes and expressed sequences were identified that demonstrated a ‡ 2-fold difference in expression between hepatocytes from the two different zones of the liver. A subset of 20 genes was additionally analyzed by real-time RT-PCR, validating the results obtained by the microarray analysis. Several of the differentially expressed genes encoded key enzymes of intermediary metabolism, including those involved in glycolysis and gluconeogenesis, fatty acid degradation, cholesterol and bile acid metabolism, amino acid degradation and ammonia utilization. In addition, several enzymes of phase I and phase II of xenobiotic metabolism were differentially expressed in periportal and perivenous hepatocytes. Our results confirm previous findings on metabolic zonation in liver, and extend our knowledge of the regulatory mechanisms at the transcriptional level.Abbreviations GS, glutamine synthetase.
Perfusion MRI is predictive in distinguishing glioblastomas from metastases, CNS lymphomas and other gliomas vs MRI and magnetic resonance spectroscopy.
Promyelocytic leukemia (PML) and Cajal bodies are mobile subnuclear organelles, which are involved in activities like RNA processing, transcriptional regulation, and antiviral defense. A key parameter in understanding their biological functions is their mobility. The diffusion properties of PML and Cajal bodies were compared with a biochemically inactive body formed by aggregates of murine Mx1 by using single-particle tracking methods. The artificial Mx1-yellow fluorescent protein body showed a very similar mobility compared with PML and Cajal bodies. The data are described quantitatively by a mechanism of nuclear body movement consisting of two components: diffusion of the body within a chromatin corral and its translocation resulting from chromatin diffusion. This finding suggests that the body mobility reflects the dynamics and accessibility of the chromatin environment, which might target bodies to specific nuclear subcompartments where they exert their biological function.C ajal and promyelocytic leukemia (PML) bodies are essential components of the nucleus that are thought to contain activities for RNA processing, transcriptional regulation, and antiviral defense. For understanding their biological functions, parameters have to be identified that characterize their mobility and lead to a localization of Cajal and PML bodies at their target sites in the nucleus. Whereas Cajal bodies are often found associated to several different small nuclear RNA and small nucleolar RNA gene loci as well as histone gene loci (1-5), PML bodies are frequently located in the MHC gene region (6). For both nuclear bodies, different types of movements were described and assigned to distinct subgroups of Cajal and PML bodies (7-12). The analysis of a baby hamster kidney cell line revealed that a fraction of PML bodies moved over longer distances and in an energy-dependent manner. These faster moving bodies were not observed in HeLa cells (8). In a detailed study of Cajal bodies in HeLa cells, an anomalous diffusion behavior and an ATP-and transcription-dependent association with chromatin was reported (7).Here, the mobility of PML and Cajal bodies has been compared with the nuclear body-like structures formed by Mx1 protein fused to yellow fluorescent protein (YFP). Mx proteins are IFN-induced GTPases of the dynamin super family involved in defense mechanisms against RNA viruses (13). The murine Mx1 protein, 72 kDa in size, has a natural nuclear localization sequence sequence and displays a nuclear body-like distribution (14,15). In contrast to the Mx1 WT protein, the Mx1-YFP construct studied has no antiviral activity as tested with influenza and Thogoto virus infection and formed crystals (S. Stertz and O. Haller, personal communication). The diffusion properties of this bona fide biologically inert body were used as a reference to identify principles determining the mobility of bodies within the nucleus. Cell Culture and Transfection. HeLa cells (ATCC CCL-2) were cultured on 12-mm glass coverslips for immunofluorescence or 35-...
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