Small-scale tests to investigate the dynamics of finite-sized dry granular avalanches and forces on a wall-like obstacle

Small-scale laboratory tests investigate the force from finite-sized granular avalanches on a wall. First, the reference flows, in absence of the wall, were analysed in a wide range of slopes from a minimum angle for which no flow is possible to a critical angle for which the flow becomes very dilute. The changes in thickness and velocity over time exhibit transitions at the minimum slope angle and at intermediate slopes. Then the normal force exerted on a wall spanning the flow was measured. It is notable that the transitions detected in reference flows had a direct effect on the force. The maximum force was equal to the kinetic force of the incoming flow at high slopes, whereas it scaled like hydrostatic force at lower slopes. This is the effect of the dense-to-dilute transition. Furthermore, the maximum force at low slopes was found to be several times greater than the hydrostatic force of the incoming flow. This finding is explained by the considerable contribution of the stagnant zone formed upstream of the wall. Furthermore, the jamming transition was highlighted at the avalanche standstill by the collapse of the residual force on the wall when approaching the minimum angle for which no flow is possible. These results are useful for the design of protection dams against rapid mass movements.     

Dorsoventral patterning in the Drosophila retina by wingless

The eye imaginal disc displays dorsal-ventral (D-V) and anterior-posterior polarity prior to the onset of differentiation, which initiates at the intersection of the D-V midline with the posterior margin. As the wave of differentiation progresses anteriorly, additional asymmetry develops as ommatidial clusters rotate coordinately in opposite directions in the dorsal and ventral halves of the disc; this forms a line of mirror-image symmetry, the equator, which coincides with the D-V midline of the disc. How D-V pattern is established and how it relates to ommatidial rotation are unknown. Here we address this question by assaying the expression of various asymmetric markers under conditions that lead to ectopic differentiation, such as removal of patched or wingless function. We find that D-V patterning develops gradually and that wingless plays an important role in setting up this pattern. We show that wingless is necessary and sufficient to induce dorsal expression of the gene mirror prior to the start of differentiation and also to restrict the expression of the WR122 marker to differentiating photoreceptors near the equator. In addition, we find that manipulations in wingless expression shift the D-V axis of the disc as evidenced by changes in the expression domains of asymmetric markers, the position of the site of initiation and the equator, and the pattern of epithelial growth. Thus, Wg appears to coordinately regulate multiple events related to D-V patterning in the developing retina.     

Role of the morphogenetic furrow in establishing polarity in the Drosophila eye

The Drosophila retina is a crystalline array of 800 ommatidia whose organization and assembly suggest polarization of the retinal epithelium along anteroposterior and dorsoventral axes. The retina develops by a stepwise process following the posterior-to-anterior progression of the morphogenetic furrow across the eye disc. Ectopic expression of hedgehog or local removal of patched function generates ectopic furrows that can progress in any direction across the disc leaving in their wake differentiating fields of ectopic ommatidia. We have studied the effect of these ectopic furrows on the polarity of ommatidial assembly and rotation. We find that the anteroposterior asymmetry of ommatidial assembly parallels the progression of ectopic furrows, regardless of their direction. In addition, ommatidia developing behind ectopic furrows rotate coordinately, forming equators in various regions of the disc. Interestingly, the expression of a marker normally restricted to the equator is induced in ectopic ommatidial fields. Ectopic equators are stable as they persist to adulthood, where they can coexist with the normal equator. Our results suggest that ectopic furrows can impart polarity to the disc epithelium, regarding the direction of both assembly and rotation of ommatidia. We propose that these processes are polarized as a consequence of furrow propagation, while more global determinants of dorsoventral and anteroposterior polarity may act less directly by determining the site of furrow initiation.     

Day and night dysfunction in intraretinal melatonin and related indoleamines metabolism, correlated with the development of glaucoma-like disorder in an avian model

As previous studies have suggested that melatonin and serotonin may be involved in the regulation of intraocular pressure, retinal concentrations of melatonin, 5-HT, and related indoleamines measured at day and at night were studied during the development of a glaucoma-like disorder with increased intraocular pressure in the al mutant quail. Indoleamine levels were determined by HPLC with electrochemical detection in 1-month-, 3-month-, and 7-month-old al mutant and control quails. Morphology and numbers of melatonin-synthesizing and 5-HT-containing cells, labelled immunohistochemically with an anti-hydroxyindol-0-methyltransferase (HIOMT) antibody and an anti-5-HT antibody, respectively, were studied. Major findings were that: (1) no significant changes in morphology of melatonin-synthesizing cells or in the morphology and density of 5-HT-containing amacrine cells were observed during the development of glaucoma: (2) 5-HT metabolism was modified during the night at 1 month of age and during the day after 3 months; and (3) melatonin metabolism was modified during the night at 7 months and during the day after 3 months. These results demonstrate a relationship between the temporal evolution of this avian glaucoma and a dysfunction in indoleamine retinal metabolism.     

Silica Nanostructures Produced Using Diatom Peptides with Designed Post‐Translational Modifications

Diatoms produce intricately patterned silica structures under ambient conditions, a process initiated by post‐translationally modified silaffin peptides that nucleate silicic acid. Designing these peptides would enable the production of silica nanostructures with desired properties; however, the functional effects of modifications are poorly understood. Here, Escherichia coli is used to express and modify recombinant silaffin R5 peptide from the diatom Cylindrotheca fusiformis. A library of 38 enzymes is tested for R5 modifications in vitro, from which active methyltransferases, kinases, acetyltransferases, oxidases, and myristoyltransferases are identified from diatoms, humans, yeast, and bacteria. Modified R5 peptides are used for silica precipitation and the impacts on particle size, shape, porosity, and surface area are quantified. In vivo pathways are designed to coexpress R5 and a modifying enzyme and the resulting peptide is used to nucleate silica nanostructures with controlled size (100–3500 nm), porosity (20–635 m² g^?1), or embedded with melanin. It is found that phosphorylation reduces the need for inorganic phosphate during silica synthesis. The simultaneous methylation and phosphorylation of R5 leads to smaller particles requiring less inorganic phosphate. Inspired by diatoms, the use of post‐translationally modified peptides will enable the control of silica morphology under ambient conditions, with potential applications in electronics and photonics.