Structure-Function Relations and Rigidity Percolation in the Shear Properties of Articular Cartilage

Among mammalian soft tissues, articular cartilage is particularly interesting because it can endure a lifetime of daily mechanical loading despite having minimal regenerative capacity. This remarkable resilience may be due to the depth-dependent mechanical properties, which have been shown to localize strain and energy dissipation. This paradigm proposes that these properties arise from the depth-dependent collagen fiber orientation. Nevertheless, this structure-function relationship has not yet been quantified. Here, we use confocal elastography, quantitative polarized light microscopy, and Fourier-transform infrared imaging to make same-sample measurements of the depth-dependent shear modulus, collagen fiber organization, and extracellular matrix concentration in neonatal bovine articular cartilage. We find weak correlations between the shear modulus |G^∗| and both the collagen fiber orientation and polarization. We find a much stronger correlation between |G^∗| and the concentration of collagen fibers. Interestingly, very small changes in collagen volume fraction v_c lead to orders-of-magnitude changes in the modulus with |G^∗| scaling as (v_c – v₀)^ξ. Such dependencies are observed in the rheology of other biopolymer networks whose structure exhibits rigidity percolation phase transitions. Along these lines, we propose that the collagen network in articular cartilage is near a percolation threshold that gives rise to these large mechanical variations and localization of strain at the tissue’s surface.     

Redundancy and cooperativity in the mechanics of compositely crosslinked filamentous networks

The cytoskeleton of living cells contains many types of crosslinkers. Some crosslinkers allow energy-free rotations between filaments and others do not. The mechanical interplay between these different crosslinkers is an open issue in cytoskeletal mechanics. Therefore, we develop a theoretical framework based on rigidity percolation to study a generic filamentous system containing both stretching and bond-bending forces to address this issue. The framework involves both analytical calculations via effective medium theory and numerical simulations on a percolating triangular lattice with very good agreement between both. We find that the introduction of angle-constraining crosslinkers to a semiflexible filamentous network with freely rotating crosslinks can cooperatively lower the onset of rigidity to the connectivity percolation threshold-a result argued for years but never before obtained via effective medium theory. This allows the system to ultimately attain rigidity at the lowest concentration of material possible. We further demonstrate that introducing angle-constraining crosslinks results in mechanical behaviour similar to just freely rotating crosslinked semflexible filaments, indicating redundancy and universality. Our results also impact upon collagen and fibrin networks in biological and bio-engineered tissues.     

Effect of Extracellular Factors on Growth and Dimorphism of Rhizopus oryzae with Multiple Enzyme Synthesizing Ability

Rhizopus oryzae PR7 MTCC 9642 was a dimorphic fungus that showed a regular 90 days cycle of filament (mycelium) to pellet (yeast) transformation through a distinct bottom dwelling intermediate state and the pellets never revert back to filamentous form. Apart from the normal cycle, high temperature (37°C and above) and extreme pH also induced the yeast formation. Among the ions tested, calcium and chloride ions were found to restore the filamentous morphology, even in extreme pH and temperature. Cysteine HCl also played noteworthy role in maintaining mycelial growth even at adverse condition. Immobilized spores showed the appearance of intermediate form instead of typical yeast form even at high temperature. The strain could produce a number of extracellular hydrolytic enzymes like cellulolytic, xylanolytic, pectinolytic and amylolytic enzymes. The pellet and mycelial forms were found to be a better producer of cellulase–lignocellulase enzymes and amylolytic enzymes respectively, which might be correlated with their infectivity. Increase in inoculum size, agitation during cultivation, change in carbon and nitrogen source failed to induce mycelial growth in extreme conditions, which might be explained as irreversible change of configuration of protein responsible for mycelial development.     

Exome Capture Reveals ZNF423 and CEP164 Mutations, Linking Renal Ciliopathies to DNA Damage Response Signaling

Nephronophthisis-related ciliopathies (NPHP-RC) are degenerative recessive diseases that affect kidney, retina, and brain. Genetic defects in NPHP gene products that localize to cilia and centrosomes defined them as "ciliopathies." However, disease mechanisms remain poorly understood. Here, we identify by whole-exome resequencing, mutations of MRE11, ZNF423, and CEP164 as causing NPHP-RC. All three genes function within the DNA damage response (DDR) pathway. We demonstrate that, upon induced DNA damage, the NPHP-RC proteins ZNF423, CEP164, and NPHP10 colocalize to nuclear foci positive for TIP60, known to activate ATM at sites?of DNA damage. We show that knockdown of CEP164 or ZNF423 causes sensitivity to DNA damaging agents and that cep164 knockdown in zebrafish results in dysregulated DDR and an NPHP-RC phenotype. Our findings link degenerative diseases of the kidney and retina, disorders of increasing prevalence, to mechanisms of DDR. PAPERFLICK:     

Properties of the Group IV phospholipase A2 family

The Group IV phospholipase A₂ family is comprised of six intracellular enzymes commonly called cytosolic phospholipase A₂ (cPLA₂) , cPLA₂β, cPLA₂γ, cPLA₂δ, cPLA₂ε and cPLA₂ζ. They are most homologous to phospholipase A and phospholipase B/lysophospholipases of filamentous fungi particularly in regions containing conserved residues involved in catalysis. However, a number of other serine acylhydrolases (patatin, Group VI PLA₂s, Pseudomonas aeruginosa ExoU and NTE) contain the Ser/Asp catalytic dyad characteristic of Group IV PLA₂s, and recent structural analysis of patatin has confirmed its structural similarity to cPLA₂. A characteristic of all these serine acylhydrolases is their ability to carry out multiple reactions to varying degrees (PLA₂, PLA₁, lysophospholipase and transacylase activities). cPLA₂, the most extensively studied Group IV PLA₂, is widely expressed in mammalian cells and mediates the production of functionally diverse lipid products in response to extracellular stimuli. It has PLA₂ and lysophospholipase activities and is the only PLA₂ that has specificity for phospholipid substrates containing arachidonic acid. Because of its role in initiating agonist-induced release of arachidonic acid for the production of eicosanoids, cPLA₂ activation is important in regulating normal and pathological processes in a variety of tissues. Current information available about the biochemical properties and tissue distribution of other Group IV PLA₂s suggests they may have distinct mechanisms of regulation and functional roles.     

Glucosides from Curculigo orchioides

From the rhizomes of Curculigo orchioides two phenolic glucosides named orchiosides A and B were isolated besides four known compounds and their structures were elucidated by the combination of 2D-NMR analysis, mass spectrometry and chemical evidences.     

Hopane-type saponins from Glinus lotoides Linn

Seven hopane-type saponins were isolated from the methanol extract of Glinus lotoides. Six of them were identified as novel compounds and designated as lotoideside A [3-O-beta-D-xylopyranosyl (1-->2)-alpha-L-rhamnopyranosyl-6 alpha-O-beta-D-xylopyranosyl-22-beta-O-beta-D-glucopyranosyl-16 beta-hydroxy hopane (1)], lotoideside B [3-O-beta-D-xylopyranosyl (1-->2)-alpha-L-rhamnopyranosyl-22-beta-O-beta-D-glucopyranosyl-6 alpha,16 beta-dihydroxyhopane (2)], lotoideside C [3-OD-xylopyranosyl-6 alpha-O-beta-D-xylopyranosyl-16 beta-O-beta-D-xylopyranosyl-22 beta-hydroxyhopane (3)], lotoideside D [3-O-beta-D-xylopyranosyl-16 beta-O-alpha-L-arabinopyranosyl-6 alpha,22-beta-dihydroxyhopane (4)], lotoideside E [3-O-beta-D-xylopyranosyl-6 alpha-O-beta-D-xylopyranosyl-16 beta,22-beta-dihydroxyhopane (5)], and lotoideside F [3-O-beta-D-xylopyranosyl-22-beta-O-beta-D-glucopyranosyl-16 beta-hydroxyhopan-6-one (6)]. The known compound succulentoside B (7) was also encountered. Their structures were elucidated on the basis of one-and two-dimensional NMR spectroscopic techniques, ESIMS and chemical evidences.     

Root associated iron oxidizing bacteria increase phosphate nutrition and influence root to shoot partitioning of iron in tolerant plant Typha angustifolia

Aims

Typha angustifolia is a heavy metal tolerant plant that grows in a uranium mine tailings highly contaminated with iron. In this study three iron oxidizing microbes (FeOBs) isolated from Typha rhizoplane were investigated for their role in plant growth promotion (PGP). Their effect on iron nutrition in Typha under iron replete and excess condition was also evaluated.

Methods

The PGP activities of the FeOBs were studied by measuring their influence on plant growth. To investigate the mechanism of growth promotion their ability to solubilize phosphate, and to produce Indole acetic acid and siderophores were studied. The influence of the FeOBs on root to shoot partitioning of iron was tested by measuring total iron content in roots and shoots treated with microbes.

Results

The FeOBs were named as Paenibacillus cookii JGR8, (MTCC12002), Pseudomonas jaduguda JGR2 (LMG25820) and Bacillus megaterium JGR9 (MTCC12001). The siderophore producers, influenced iron accumulation in the plant root. Additionally P. pseudoalcaligenes JGR2 increased shoot iron content overcoming the root- shoot barrier that allows Typha to exclude metals from its shoot. Among the PGP mechanisms tested, ability to solubilize phosphate appeared to be most significant for increasing the plant biomass.

Conclusion

FeOBs that produce siderophore increased iron content in plant and therefore can be of immense biotechnological importance. However Biomass increase was directly correlated with increased phosphate acquisition and not with enhanced iron accumulation in Typha.