La dormance embryonnaire chez Taxus baccata: Influence de la composition du milieu liquide sur I'induction de la germination Par

Embryo dormancy of Taxus baccata var. fastigiata is eliminated when cultured continuously in nutritive liquid medium. An equivalent percentage of germination is obtained when the embryos are transferred to agar medium after 8 days of liquid culture. There is no morphological development of the embryo during the period in the liquid medium. But we have ascertained that water-soluble germination inhibitors present in the embryo are leached out into the medium, permitting germination. Germination is totally absent when the embryos are cultured continuously in distilled water, alone or with minerals; incidental in sucrose solution; and maximal when the medium contains sucrose and Ca²⁺ or K⁺ ions. The extent of germination on agar medium depends upon the composition of the liquid medium in which the embryos are cultured for the initial 8 days. But this preliminary culture in the liquid medium does not always remove the endogenous inhibitors, irrespective of its composition. This can be achieved only in the presence of sucrose; and this process can be made more effective by the addition of Ca²⁺ ions.     

Spatial and temporal variation in diets of the crabs <Emphasis Type="Italic">Metopograpsus frontalis</Emphasis> (Grapsidae) and <Emphasis Type="Italic">Perisesarma bidens</Emphasis> (Sesarmidae): implications for mangrove food webs

The diets of the mangrove crabs, Metopograpsus frontalis Miers and Perisesarma bidens de Haan, were investigated monthly for 13 months at two Hong Kong mangroves, to examine possible spatial and temporal influences on their feeding ecology. In both species, a higher degree of gut fullness was observed in summer (May–September) than in winter, suggesting a reduction in winter foraging activity. M. frontalis was omnivorous, with animal and plant materials and inorganic sediments being the major food items. P. bidens was detritivorous, with plant materials and inorganic sediment dominating the gut contents. M. frontalis is, therefore, an opportunistic feeder, whilst P. bidens, like many other members of the Sesarmidae, is a detritivore. Some degree of seasonal variation was shown in the diet of M. frontalis (with more algal material in winter) and P. bidens (with more sediments in summer), but diets were similar between sexes in both species. The dietary pattern of M. frontalis also varied between sites. The diets of the crabs, therefore, appear to be a result of the interplay between the seasonal, physical climate and biological factors, especially food availability and the crabs’ ecology. Results suggest that the predatory role of Metopograpsus, which has been poorly studied, is potentially important to estuarine food webs; whilst the trophic importance of sesarmid crabs, such as Perisesarma, especially in mangrove outwelling, should be critically re-evaluated.     

New carbon-linked azole oxazolidinones with improved potency and pharmacokinetics

Substitution of phenyl oxazolidinones with carbon-linked azoles resulted in the discovery of a new class of potent oxazolidinones that have excellent Gram-positive activity. In addition, replacement of the C-5 acetamide side chains with a 4-methyl triazole diminished monoamine oxidase activity. The synthesis and biological evaluation of these compounds are reported.     

p21 and retinoblastoma protein control the absence of DNA replication in terminally differentiated muscle cells

During differentiation, skeletal muscle cells withdraw from the cell cycle and fuse into multinucleated myotubes. Unlike quiescent cells, however, these cells cannot be induced to reenter S phase by means of growth factor stimulation. The studies reported here document that both the retinoblastoma protein (Rb) and the cyclin-dependent kinase (cdk) inhibitor p21 contribute to this unresponsiveness. We show that the inactivation of Rb and p21 through the binding of the adenovirus E1A protein leads to the induction of DNA replication in differentiated muscle cells. Moreover, inactivation of p21 by E1A results in the restoration of cyclin E-cdk2 activity, a kinase made nonfunctional by the binding of p21 and whose protein levels in differentiated muscle cells is relatively low in amount. We also show that restoration of kinase activity leads to the phosphorylation of Rb but that this in itself is not sufficient for allowing differentiated muscle cells to reenter the cell cycle. All the results obtained are consistent with the fact that Rb is functioning downstream of p21 and that the activities of these two proteins may be linked in sustaining the postmitotic state.     

Role of cadherin-17 in oncogenesis and potential therapeutic implications in hepatocellular carcinoma

Cadherin is an important cell adhesion molecule that plays paramount roles in organ development and the maintenance of tissue integrity. Dysregulation of cadherin expression is often associated with disease pathology including tissue dysplasia, tumor formation, and metastasis. Cadherin-17 (CDH17), belonging to a subclass of 7D-cadherin superfamily, is present in fetal liver and gastrointestinal tract during embryogenesis, but the gene becomes silenced in healthy adult liver and stomach tissues. It functions as a peptide transporter and a cell adhesion molecule to maintain tissue integrity in epithelia. However, recent findings from our group and others have reported aberrant expression of CDH17 in major gastrointestinal malignancies including hepatocellular carcinoma (HCC), stomach and colorectal cancers, and its clinical association with tumor metastasis and advanced tumor stages. Furthermore, alternative splice isoforms and genetic polymorphisms of CDH17 gene have been identified in HCC and linked to an increased risk of HCC. CDH17 is an attractive target for HCC therapy. Targeting CDH17 in HCC can inhibit tumor growth and inactivate Wnt signaling pathway in concomitance with activation of tumor suppressor genes. Further investigation on CDH17-mediated oncogenic signaling and cognate molecular mechanisms would shed light on new targeting therapy on HCC and potentially other gastrointestinal malignancies.