Non-linear signaling for pattern formation?

Developmental pathways are often simplified as linear cascades of gene activation caused by initial signaling events. Recent data, however, support a more complex view in which non-linear responses to signals are important for pattern formation. First, a positive feedback loop may regulate cellular patterning in the Arabidopsis epidermis. Second, an asymmetric auxin distribution that organizes pattern in the distal root tip may be established by positive feedback.     

Plant mRNA 3′-end formation

Our understanding of how the 3 ends of mRNAs are formed in plants is rudimentary compared to what we know about this process in other eukaryotes. The salient features of plant pre-mRNAs that signal cleavage and polyadenylation remain obscure, and the biochemical mechanism is as yet wholly uncharacterised. Nevertheless, despite the lack of universally conserved cis-acting motifs, a common underlying architecture is emerging from functional analyses of plant poly(A) signals, allowing meaningful comparison with components of poly(A) signals in other eukaryotes. A plant poly(A) signal consists of one or more near-upstream elements (NUE), each directing processing at a poly(A) site a short distance downstream of it, and an extensive far-upstream element (FUE) that enhances processing efficiency at all sites. By analogy with other systems, a model for a plant 3-end processing complex can be proposed. Plant poly(A) polymerases have been isolated and partially characterised. These, together with hints that some processing factors are conserved in different organisms, opens promising avenues toward initial characterisation of the trans-acting factors involved in 3-end formation of mRNAs in higher plants.     

Does collagen microunfolding stimulate fibril formation?

The data on the effect of temperature on the kinetics of collagen fibril formation at physiological pH values and ionic strength in the temperature range 26–39°C have been analyzed. The temperature of 35°C optimal for collagen fibril formation has been defined as the point of inflection for half-maximal turbidity and collagen molecule microunfolding values, which corresponds to the temperature of the first transition on the heat absorption curve. The temperature range (32–35°C) in which collagen microunfolding stimulates fibril formation has been determined.     

Axioms and axes in leaf formation?

Formation of leaves and floral organs involves down-regulation of meristem-specific homeobox genes, and de novo expression of genes for organ identity, growth and patterning. Genes required for all these aspects of organ formation have been identified. The challenge now is to establish how they interact to direct organogenesis.     

Phosphorus-containing dendrimers against α-synuclein fibril formation

The aim of this work was to study the effect of phosphorus-containing dendrimers (generations G3 and G4) on the fibrillation of α-synuclein (ASN). The inhibition of fibril formation (filamentous and aggregates) is a potential therapeutic strategy for neurodegenerative disorders such as Parkinson's and other motor disorder neurodegenerative diseases. The interaction between phosphorus-containing dendrimers and ASN was studied by fluorescence spectroscopy. The decrease in the fluorescence intensity of intrisinic tyrosine was the most marked change in the fluorescence intensity observed upon addition of dendrimers. Furthermore, the effect of dendrimers on ASN fibril formation was studied using circular dichroism (CD) spectroscopy and CD studies were complemented by fluorescence assays using the dye thioflavin T (ThT). The results showed that phosphorus-containing dendrimers G3 and G4 inhibited fibril formation, when they were used in the ASN/dendrimer ratios 1:0.1 and 1:0.5. However, the higher concentrations of dendrimers did not show this effect.     

Hybrid formation within the genus Leishmania?

Leishmanial organisms isolated from a desert rodent (Psammomys obesus) and a feral dog (Canis familiaris) in the Eastern Province of Saudi Arabia were isoenzymically distinct from Leishmania major and L. arabica, organisms usually associated with human and wild animal cutaneous leishmaniasis in this area. Further examination of isoenzyme banding patterns of cloned populations of these organisms, together with karyotyping using orthogonal field alternation gel electrophoresis and the use of highly specific kinetoplast DNA probes, has produced evidence suggesting that these organisms isolated from the dog and the rodent are hybrids of L. major and L. arabica.     

Surface-directed structure formation of β-lactoglobulin inside droplets

The morphology of β-lactoglobulin structures inside droplets was studied during aggregation and gelation using confocal laser scanning microscopy (CLSM) equipped with a temperature stage and transmission electron microscopy (TEM). The results showed that there is a strong driving force for the protein to move to the interface between oil and water in the droplet, and the β-lactoglobulin formed a dense shell around the droplet built up from the inside of the droplets. Less protein was found inside the droplets. The longer the β-lactoglobulin was allowed to aggregate prior to gel formation, the larger the part of the protein went to the interface, resulting in a thicker shell and very little material being left inside the droplets. The droplets were easily deformed because no network stabilizes them. When 0.5% emulsifier, polyglycerol polyresinoleat (PGPR), was added to the oil phase, the β-lactoglobulin was situated both inside the droplets and at the interface between the droplets and the oil phase; when 2% PGPR was added, the β-lactoglobulin structure was concentrated to the inside of the droplets. The possibility to use the different morphological structures of β-lactoglobulin in droplets to control the diffusion rate through a β-lactoglobulin network was evaluated by fluorescence recovery after photobleaching (FRAP). The results show differences in the diffusion rate due to heterogeneities in the structure: the diffusion of a large water-soluble molecule, FITC-dextran, in a dense particulate gel was 1/4 of the diffusion rate in a more open particulate β-lactoglobulin gel in which the diffusion rate was similar to that in pure water.     

Can mechanics control pattern formation in plants?

Development of the plant body entails many pattern forming events at scales ranging from the cellular level to the whole plant. Recent evidence suggests that mechanical forces play a role in establishing some of these patterns. The development of cellular configurations in glandular trichomes and the rippling of leaf surfaces are discussed in depth to illustrate how intricate patterns can emerge from simple and well-established molecular and cellular processes. The ability of plants to sense and transduce mechanical signals suggests that complex interactions between mechanics and chemistry are possible during plant development. The inclusion of mechanics alongside traditional molecular controls offers a more comprehensive view of developmental processes.     

Free radical–induced megamitochondria formation and apoptosis

Pathophysiological meaning and the mechanism of the formation of megamitochondria (MG) induced under physiological and pathological conditions remain obscure. We now provide evidence suggesting that the MG formation may be a prerequisite for free radical-mediated apoptosis. MG were detected in primary cultured rat hepatocytes, rat liver cell lines RL-34 and IAR-20 and kidney cell line Cos-1 treated for 22 h with various chemicals known to generate free radicals: hydrazine, chloramphenicol, methyl-glyoxal-bis-guanylhydrazone, indomethacin, H₂O₂, and erythromycin using a fluorescent dye Mito Tracker Red CMXRos (CMXRos) for confocal laser microscopy and also by electron microscopy. Remarkable elevations of the intracellular level of reactive oxygen species (ROS), monitored by staining of cells with a fluorescent dye carboxy-H₂-DCFDA, were detected before MG were formed. Prolongation of the incubation time with various chemicals, specified above, for 36 h or longer has induced distinct structural changes of the cell, which characterize apoptosis: condensation of nuclei, the formation of apoptotic bodies, and the ladder formation. Cells treated with the chemicals for 22 h were arrested in G₁ phase, and apoptotic sub-G₁ populations then became gradually increased. The membrane potential of MG induced by chloramphenicol detected by CMXRos for flow cytometry was found to be decreased compared to that of mitochondria in control cells. Rates of the generation of H₂O₂ and O₂⁻ from MG isolated from the liver of rats treated with chloramphenicol or hydrazine were found to be lower than those of mitochondria of the liver of control animals. We suggest, based on the present results together with our previous findings, that the formation of MG may be an adaptive process at a subcellular level to unfavorable environments: when cells are exposed to excess amounts of free radicals mitochondria become enlarged decreasing the rate of oxygen consumption. Decreases in the oxygen consumption of MG may result in decreases in the rate of ROS production as shown in the present study. This will at the same time result in decreases in ATP production from MG. If cells are exposed to a large amount of free radicals beyond a certain period of time, lowered intracellular levels of ATP may result in apoptotic changes of the cell.     

Kin selection and reciprocity in flight formation?

The reasons for conspicuous "V" and other flight formationsin birds are debated. Theory and recent empirical advances showthat energy saving is one important function of flight formations,but some aspects remain poorly understood. Combining theoriesof animal flight and sociality, we suggest that some of thevariation in flight formations has its base in kin selectionand reciprocation. The bird leading an acute V formation savesless energy than does the trailing participants. The disadvantageof leading is reduced in more obtuse formations, and when thelongitudinal distance between neighbors is small, the leadingbird can save about as much energy as others. Therefore, acuteV formations are predicted to occur mainly in circumstancesconducive to kin selection or reciprocity. These mechanismsseem possible, for example, in small flocks of adults with offspring,such as in swans, geese, and cranes. Inclusive fitness advantagesmay then favor an energetically expensive leader role for adults.In small groups, reciprocity is also possible among unrelatedadults that recognize each other and take turns leading theV formation. In contrast, obtuse formations are expected inlarge flocks of unrelated individuals, such as spring flocksof waders migrating long distances. Possibilities for testingthese ideas are discussed.     

Can tissue surface tension drive somite formation?

The prevailing model of somitogenesis supposes that the presomitic mesoderm is segmented into somites by a clock and wavefront mechanism. During segmentation, mesenchymal cells undergo compaction, followed by a detachment of the presumptive somite from the rest of the presomitic mesoderm and the subsequent morphological changes leading to rounded somites. We investigate the possibility that minimization of tissue surface tension drives the somite sculpting processes. Given the time in which somite formation occurs and the high bulk viscosities of tissues, we find that only small changes in shape and form of tissue typically occur through cell movement driven by tissue surface tension. This is particularly true for somitogenesis in the zebrafish. Hence it is unlikely that such processes are the sole and major driving force behind somite formation. We propose a simple chemotactic mechanism that together with heightened adhesion can account for the morphological changes in the time allotted for somite formation.     

G-octamer formation from N⁹ modified guanine derivatives

The properties of the self-assembly of two lipophilic guanine derivatives, 2',3',5'-O-tris(tert-butyldimethylsilyl)-guanosine and N?-(3,5-bis(tert-butyldimethylsilyloxy)-benzyl)-guanine, are described. In the presence of K+, both guanine derivatives self-associate into D?-symmetric octamers consisting of two G-quartets stacked around a central ion.     

Penicillinase (β-lactamase) formation by blue-green algae

-Lactamase (penicillinase) activity was found in a number of strains of blue-green algae. In some cases, this enzyme permitted algae to overcome the inhibitory effects of penicillin. Production and localization of -lactamase were studied in a unicellular species, Coccochloris elabens (strain 7003), and in a filamentous, nitrogen-fixing Anabaena species (strain 7120). When cells were grown in a neutral medium with NaNO₃ as N source, the pH rose during growth; at a pH of about 10, most of the enzyme was extracellular and all the cell-bound enzyme was expressed equally well in intact or disrupted cells. If the pH was kept near neutrality during growth by gassing with CO₂ in N₂ or by growth under conditions of N₂ fixation, the enzyme remained cell-bound and cryptic for most of the growth phase, being measurable only after cells were disrupted. The enzymes from strains 7003 and 7120 had greater activity on benzyl penicillin and other penicillins than on cephalo-sporins. Some differences were observed in the substrate profiles of penicillinases from the two strains against different penicillins.A preliminary account of this work was presented at the 1974 meetings of the American Society for Microbiology in Chicago (Abstracts of Meetings, M37)     

A Role for auxin during actinorhizal symbioses formation?

The symbiotic interaction between the soil bacteria Frankia and actinorhizal plants leads to the formation of nitrogen-fixing nodules resembling modified lateral roots. Little is known about the signals exchanged between the two partners during the establishment of these endosymbioses. However, a role for plant hormones has been suggested.Recently, we studied the role of auxin influx activity during actinorhizal symbioses. An inhibitor of auxin influx was shown to perturb nodule formation. Moreover we identified a functional auxin influx carrier that is produced specifically in Frankia-infected cells. These results together with previous data showing auxin production by Frankia lead us to propose a model of auxin action during the symbiotic infection process.Key words: lateral roots, nitrogen fixation, Frankia, AUX1, actinorhizal symbioses, phenylacetic acid, auxin influxActinorhizal symbioses result from the interaction between the soil actinomycete Frankia and plants belonging to eight angiosperm families collectively called actinorhizal plants.¹ This symbiotic interaction leads to the formation of a new organ on the root system, the actinorhizal nodule, where the bacteria are hosted and fix nitrogen.² Unlike legume nodules, actinorhizal nodules are structurally and developmentally related to lateral roots.³ Little is known about the signals exchanged between the two partners during the establishment of the symbiosis.² Diffusible signals are emitted by Frankia at early stages of the interaction resulting in root hair deformation.² The chemical nature of these signals remains unknown, however, detailed studies revealed that they are different from rhizobial Nod factors.⁴ Phytohormones are chemicals that control many developmental processes⁵ and have been linked to many plant-microbe interactions. Recently, we studied the role of auxin influx in actinorhizal nodule formation in the tropical tree Casuarina glauca.⁶