Synthesis of protected 2-amino-2-deoxy-D-xylothionolactam derivatives and some aspects of their reactivity

The synthesis of polyfunctionalized delta-lactams as key intermediates of glycomimetics in the 2-acetamido-2-deoxy sugar series is presented. Starting from a chiral gamma-amino vinylic ester synthesized from Garner's aldehyde and after regioselective reduction, 1-azido-3-(N-tert-butyloxycarbonyl-2,2-dimethyloxazolidin-4-yl)-2-propene was obtained. Next, a cis-dihydroxylation reaction provided the protected D-xylitol and L-arabinitol azides. A simple protection-deprotection sequence, followed by an oxidation and a reductive cyclization, led to protected 2-amino-delta-lactams bearing a tert-butyloxycarbonyl group on the amine functionality. To explore the reactivity of such compounds, activation of the lactam into the corresponding thionolactam was performed. The resulting 2-amino-D-xylothionolactam derivative, a versatile intermediate, allowed access to a first generation of protected 2-amino-D-xylosamidoxime derivatives which are of interest as precursors of N-acetylhexosaminidase and N-acetylglucosaminyltransferase inhibitors. In this series of compounds, epimerization at C-2 was observed. AM(1) calculations performed on these analogs showed that they adopted a B(2,5) conformation and that the axial epimer was favored in the protected series whereas the equatorial epimer was preferred in the unprotected series.     

Laminin alpha5 chain is required for intestinal smooth muscle development

Laminins (comprised of alpha, beta, and gamma chains) are heterotrimeric glycoproteins integral to all basement membranes. The function of the laminin alpha5 chain in the developing intestine was defined by analysing laminin alpha5(-/-) mutants and by grafting experiments. We show that laminin alpha5 plays a major role in smooth muscle organisation and differentiation, as excessive folding of intestinal loops and delay in the expression of specific markers are observed in laminin alpha5(-/-) mice. In the subepithelial basement membrane, loss of alpha5 expression was paralleled by ectopic or accelerated deposition of laminin alpha2 and alpha4 chains; this may explain why no obvious defects were observed in the villous form and enterocytic differentiation. This compensation process is attributable to mesenchyme-derived molecules as assessed by chick/mouse alpha5(-/-) grafted associations. Lack of the laminin alpha5 chain was accompanied by a decrease in epithelial alpha3beta1 integrin receptor expression adjacent to the epithelial basement membrane and of Lutheran blood group glycoprotein in the smooth muscle cells, indicating that these receptors are likely mediating interactions with laminin alpha5-containing molecules. Taken together, the data indicate that the laminin alpha5 chain is essential for normal development of the intestinal smooth muscle and point to possible mesenchyme-derived compensation to promote normal intestinal morphogenesis when laminin alpha5 is absent.     

T1alpha,a lung type I cell differentiation gene,is required for normal lung cell proliferation and alveolus formation at birth

T1alpha, a differentiation gene of lung alveolar epithelial type I cells, is developmentally regulated and encodes an apical membrane protein of unknown function. Morphological differentiation of type I cells to form the air-blood barrier starts in the last few days of gestation and continues postnatally. Although T1alpha is expressed in the foregut endoderm before the lung buds, T1alpha mRNA and protein levels increase substantially in late fetuses when expression is restricted to alveolar type I cells. We generated T1alpha null mutant mice to study the role of T1alpha in lung development and differentiation and to gain insight into its potential function. Homozygous null mice die at birth of respiratory failure, and their lungs cannot be inflated to normal volumes. Distal lung morphology is altered. In the absence of T1alpha protein, type I cell differentiation is blocked, as indicated by smaller airspaces, many fewer attenuated type I cells, and reduced levels of aquaporin-5 mRNA and protein, a type I cell water channel. Abundant secreted surfactant in the narrowed airspaces, normal levels of surfactant protein mRNAs, and normal patterns and numbers of cells expressing surfactant protein-B suggest that differentiation of type II cells, also alveolar epithelial cells, is normal. Anomalous proliferation of the mesenchyme and epithelium at birth with unchanged numbers of apoptotic cells suggests that loss of T1alpha and/or abnormal morphogenesis of type I cells alter the proliferation rate of distal lung cells, probably by disruption of epithelial-mesenchymal signaling.     

Signals from lateral plate mesoderm instruct endoderm toward a pancreatic fate

During embryonic development, organs arise along the gut tube as a series of buds in a stereotyped anterior-posterior (A-P) pattern. Using chick-quail chimeras and in vitro tissue recombination, we studied the interactions governing the induction and maintenance of endodermal organ identify focusing on the pancreas. Though several permissive signals in pancreatic development have been previously identified, here we provide evidence that lateral plate mesoderm sends instructive signals to the endoderm, signals that induce expression of the pancreatic genes Pdx1, p48, Nkx6.1, glucagon, and insulin. Moreover, this instructive signal directs cells to form ectopic insulin-positive islet-like clusters in endoderm that would otherwise form more rostral organs. Once generated, endocrine cells no longer require interaction with mesoderm, but nonendocrine cells continue to require permissive signals from the mesoderm. Stimulation of activin, BMP, or retinoic acid signaling is sufficient to induce Pdx1 expression in endoderm anterior to the pancreas. Lateral plate mesoderm appears to pattern the endoderm in a posterior-dominant fashion as first noted in the patterning of the neural tube at the same embryonic stage. These findings argue for a central role of the mesoderm in coordinating the A-P pattern of all three primary germ layers.     

Multilevel phenotypic selection on morphological characters in a metapopulation of Silene tatarica

This study partitions selection in a natural metapopulation of a riparian plant species, Silene tatarica, into individual- and patch-level components by using contextual analysis, in which a patch refers to a spatially distinct stand of individual plants. We estimated selection gradients for two morphological characters (plant height and number of stems), their respective patch means, and plant density with respect to reproductive success in a two-year study. The approach was also extended to partition selection separately within habitats with varying degrees of exposure to river disturbances and herbivory. The selection differentials and gradients for plant height were positive at both individual and patch levels, with selection forces highest in the closed habitat with low exposure to disturbance. This pattern suggests that local groups with taller than average plants are more visible to pollinators than to groups that are shorter than average plants; and, within patches, individuals with short stature are visited less often than taller ones. Selection on the number of stems was in opposition at individual and patch levels. At the individual level the character was selected toward higher values, whereas selection at the patch-level favored smaller mean number of stems. The strength of the latter component was associated with the intensity of herbivory in different habitats, suggesting that the patch-level selection against a large number of stems might be due to high attractiveness of such patches to the main herbivore, reindeer. Consequently, direction and strength of selection in spatially structured populations may depend significantly on fitness effects arising at the group level.     

Changes in the LHCI aggregation state during iron repletion in the unicellular red alga Rhodella violacea

Red algae are well suited to study the effects of iron deficiency on light-harvesting complex for photosystem I (LHCI), since they are totally devoid of light-harvesting complex for photosystem II (LHCII). Iron starvation results in a reduction of the pigment content, an increase of the fluorescence yield and a new emission band at 705 nm in the 77 K fluorescence emission spectra. These changes reflect the accumulation of uncoupled, aggregated LHCI in iron-depleted cells. Reconnection of LHCI to de novo synthesized reaction center I (RCI) is the first event, which takes place after iron addition. The changes in the aggregation state of LHCI are likely to occur also in brown and green algae.