Crosstalk between H2A variant-specific modifications impacts vital cell functions

Selection of C-terminal motifs participated in evolution of distinct histone H2A variants. Hybrid types of variants combining motifs from distinct H2A classes are extremely rare. This suggests that the proximity between the motif cases interferes with their function. We studied this question in flowering plants that evolved sporadically a hybrid H2A variant combining the SQ motif of H2A.X that participates in the DNA damage response with the KSPK motif of H2A.W that stabilizes heterochromatin. Our inventory of PTMs of H2A.W variants showed that in vivo the cell cycle-dependent kinase CDKA phosphorylates the KSPK motif of H2A.W but only in absence of an SQ motif. Phosphomimicry of KSPK prevented DNA damage response by the SQ motif of the hybrid H2A.W/X variant. In a synthetic yeast expressing the hybrid H2A.W/X variant, phosphorylation of KSPK prevented binding of the BRCT-domain protein Mdb1 to phosphorylated SQ and impaired response to DNA damage. Our findings illustrate that PTMs mediate interference between the function of H2A variant specific C-terminal motifs. Such interference could explain the mutual exclusion of motifs that led to evolution of H2A variants.     

Uncertainty in Impact and Externality Assessments - Implications for Decision-Making (13 pp)

Goal, Scope and Background Many disciplines, amongst them LCIA, environmental impact and external cost assessments, are often faced with evaluating trade-offs between two or more alternative options in terms of a range of incommensurable indicators. Using process modeling and valuation, these indicators are quantified at mid- or endpoint levels. Recent discussion amongst LCA experts showed that because of the mutually exclusive aspects of uncertainty and relevance, the midpoint/endpoint debate is controversial and difficult to reconcile. This article is aimed at a more quantitative analysis of mid- and endpoint impacts, and the implications of uncertainty for decision-making. Methods The consequences for decision-making of uncertainties of endpoints are analysed quantitatively for the example of ExternE results, by employing statistical hypothesis testing. The Analytic Hierarchy Process (AHP) is then used to demonstrate the use of multi-criteria techniques at midpoint levels. Results and Discussion Statistical hypothesis testing at the endpoint level shows that for the ExternE example, probabilities of mistakenly favouring one alternative over another when they are in reality indistinguishable can be as high as 80%. Therefore, the best estimate of external cost is inadequate for most policy making purposes. Indicators at midpoint levels are more certain, but since they are only \proxy attributes\, they carry a hidden uncertainty in their relevance. Conclusion If endpoint information is too uncertain to allow a decision to be made with reasonable confidence, then the assessment can be carried out in midpoint terms. However, midpoint indicators are generally further removed from people's experience, and less relevant to the question that people actually want to solve. Nevertheless, if this ultimate question is unanswerable (within the certainty required by the decision-maker), a decision can be made on the basis of stakeholders' subjective judgments about the more certain midpoint levels. The crucial point is that these judgments are able to intuitively incorporate many aspects that impact modeling and valuation has trouble quantifying, such as perceived risk, distribution of burdens and benefits, equity, ethical, moral, religious and political beliefs and principles, immediacy and reversibility of potential impacts, voluntariness, controllability and familiarity of exposure, or perceived incompleteness of human knowledge.     

Electron microscopical and histochemical studies of differentiation and function of the cephalopod gill (Sepia officinalis L.)

Summary Phase contrast and electron microscopical investigations on the gill ofSepia officinalis L., from the stage shortly before hatching to the adult stage, demonstrate (1) peripheral respiratory epithelial areas and (2) highly folded epithelia rich in mitochondria in the concave recesses of the gill lamellae. Enzyme-histochemical and cytochemical findings, and in particular the GOT proof, suggest by analogy with the chloride cells of the teleosts that the cells of this second type of epithelium are capable of active transport, and that they probably secrete ammonia. Apparently the gill of cephalopods, too, serves both respiratory and excretory functions.This study was supported by the Deutsche Forschungsgemeinschaft     

Distribution of glucose-6-phosphatase activity in normal, hyperplastic, and preneoplastic rat liver.

The significance of glucose-6-phosphatase (G6P) expression by bile duct-like cells proliferating during hepatocarcinogenesis in the histogenesis of hepatocellular carcinoma is not clear. To this end, we measured the histochemical and biochemical activity of G6P in normal rat liver, and in rat livers in which bile duct-like proliferation was induced by either hyperplastic (bile duct ligation for 14 days or feeding alpha-naphthylisothiocyanate for 28 days) or neoplastic (feeding a choline-devoid diet containing 0.1% ethionine for 60 days) regimens. In normal, hyperplastic, and preneoplastic livers, G6P histochemical activity was confined to the hepatocytes; proliferated bile duct-like cells, like normal bile ducts, did not display visible G6P staining. When the enzyme activity was determined biochemically, however, hydrolysis of glucose-6-phosphate was observed in both parenchymal and nonparenchymal liver cells isolated from all experimental animals. In elutriated nonparenchymal fractions, G6P activity was directly proportional to the number of cells positive for gamma-glutamyl transpeptidase and cytokeratin no. 19 (markers of bile duct cells) and inversely proportional to the number of cells positive for vimentin (marker of mesenchymal cells). These results indicate that, while by light microscopy hepatic G6P histochemical activity is detectable only in the hepatocytes, the biochemical activity is also expressed in proliferating bile duct-like cells. However, the nonparenchymal activity is observed during both neoplastic and hyperplastic liver growth, thus indicating that the presence of this enzyme in bile duct-like cells proliferating during hepatocarcinogenesis should not necessarily be construed as supporting their stem cell nature nor their neoplastic commitment.     

Mutational analysis of the stability of Psb27 from Synechocystis sp. PCC 6803: implications for models of Psb27 structure and binding to CP43

Psb27 associates with the CP43 subunit of photosystem II during biogenesis of the photosystem. Several models have been proposed for the interaction between Psb27 and CP43. The utility of predictions and hypotheses arising from these models depends on the accuracy of the Psb27 structure used in the model. Two of the Psb27 structures used to model the Psb27–CP43 interaction place residue E98 on the surface of Psb27 and D14 in a position to form hydrogen bonds that stabilise the fold of the protein; however, a third structure questions the surface exposure of E98 and does not identify significant interactions of D14. Here we present evidence that D14 contributes to the thermal stability of Psb27 and that E98 is located on the surface. A D14A mutation was shown to reduce the apparent midpoint of unfolding of Psb27 by 16 °C. Four highly conserved surface residues and E98 were subject to charge-reversal mutations (R54E, R94E, E98R, E103R, R108E). The stabilities of the charge-reversal variants and the unmodified control were similar, suggesting E98 is a surface residue. Placing E98 in the correct, surface position will support more reliable models of the interaction of Psb27 with CP43.     

Broca's Region: Novel Organizational Principles and Multiple Receptor Mapping

There is a considerable contrast between the various functions assigned to Broca''s region and its relatively simple subdivision into two cytoarchitectonic areas (44 and 45). Since the regional distribution of transmitter receptors in the cerebral cortex has been proven a powerful indicator of functional diversity, the subdivision of Broca''s region was analyzed here using a multireceptor approach. The distribution patterns of six receptor types using in vitro receptor autoradiography revealed previously unknown areas: a ventral precentral transitional cortex 6r1, dorsal and ventral areas 44d and 44v, anterior and posterior areas 45a and 45p, and areas op8 and op9 in the frontal operculum. A significant lateralization of receptors was demonstrated with respect to the cholinergic M₂ receptor, particularly in area 44v+d. We propose a new concept of the anterior language region, which elucidates the relation between premotor cortex, prefrontal cortex, and Broca''s region. It offers human brain homologues to the recently described subdivision of area 45, and the segregation of the ventral premotor cortex in macaque brains. The results provide a novel structural basis of the organization of language regions in the brain.