Parturition and alate morph determination in the aphid Megoura viciae

In reproducing apterae of Megoura viciae, parturition is often completely arrested during periods of isolation from the host plant. In contrast, surgical removal of the rostrum (including the stylets), amputation of the extremities of the legs, or decapitation, all stimulate parturition away from the plant. These operations also induce alata-producing aphids to revert immediately to the production of apterae, but have no detectable effect on aptera-producers. Carbon dioxide or ether anaesthesia and nitrogen narcosis have a similar action on this maternally controlled response. Although the rostrum and tibio-tarsus bear sensilla whose removal might well be involved in inducing parturition, the influence on morph change is probably indirect and is to a great extent associated with the delay in the resumption of parturition. The effect can be reproduced by isolating individual aphids away from the food plant. The morph change cannot, however, be attributed to starvation since it also occurs when the genital pore of an actively feeding aphid is temporarily occluded. The change in physiology appears to be associated with the retention of embryos at a time when there is no sensory input from crowding.

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Résumé Chez les Megoura viciae aptères, la parturition est souvent complètement arrêtée pendant les périodes de séparation de la plante hôte. Par opposition, l'amputation chirurgicale du rostre (y compris les stylets), de l'extrémité des pattes (tarse et une partie du tibia), ou la décapitation, stimulent toutes la parturition en l'absence de la plante. Les pucerons induits à produire des ailés (élevage antérieur en groupe) retournent, après ces opérations, immédiatement vers la production d'aptères. Le dioxyde de carbone ou l'anesthésie à l'éther et la narcose à l'azote ont une action semblable sur ce déterminisme maternel. Bien que l'élimination des sensilla portées par le rostre et par l'ensemble tarse-tibia puisse être déterminante dans l'induction de la parturition, l'action sur le changement de type semble être principalement associée au retard consécutif dans la reprise de la parturition. Les anesthésiants qui, eux aussi, retardent l'apparition ou la reprise de la parturition, ont probablement une action indirecte du même type.Les pucerons groupés, isolés de la plante hôte pendant plus de 24 h, ont aussi tendance à retourner immédiatement à la production d'aptères. Ce changement de type ne peut, cependant, être attribué au jeûne puisqu'il se produit aussi quand, chez un puceron s'alimentant activement, le pore génital est momentanément bouché. Le changement physiologique semble être associé à la rétention des embryons à un moment où il n'y a pas l'influence sensorielle du groupement.Aucun de ces traitements, à l'exception du groupement, n'induit des pucerons antérieurement isolés à devenir des producteurs d'ailés.

     

Dissociation of differentiation and proliferation in the primary induction of cytolytic T lymphocytes by alloantigens

The requirement for DNA synthesis in the induction of cytolytic T lymphocytes (CTL) by alloantigens has been investigated. C57BL/6 splenic T cells purified by passage on nylon wool columns were stimulated in vitro in mixed leukocyte culture (MLC) and assayed for cytotoxicity against 51Cr-labeled target cells. With this system, CTL activity was detectable after 24 hr of MLC and reached high levels after 48 hr. Addition of cytosine arabinoside (ARA-C) or hydroxyurea to such cultures at concentrations that were sufficient to inhibit DNA synthesis by greater than 98% did not reduce CTL activity measured after 24 hr; however, the increase in activity that occurred between 24 and 48 hr in control cultures was strongly reduced (or abolished) by these drugs. Velocity sedimentation analysis of MLC cells activated for 48 hr in the presence of ARA-C further revealed that CTL precursor lymphocytes had enlarged into medium- to large-sized CTL under these conditions. These studies provide direct evidence that the primary induction of CTL by alloantigens can be dissociated into a differentiation step, which occurs within 24 hr in the absence of DNA synthesis and is accompanied by blast transformation, and a subsequent proliferation.     

Characterization of <Emphasis Type="Italic">Brassica napus</Emphasis> L. genotypes utilizing sequence-related amplified polymorphism and genotyping by sequencing in association with cluster analysis

Identifying parental combinations that exhibit high heterosis is a constant target for commercial Brassica napus L. hybrid development programs. Finding high heterotic parental combinations can require hundreds of test crosses and years of yield evaluation. Heterotic pool development could be used to divide breeding material into specific breeding pools and focus the number of parental combinations created. Here, we report the genotypic characterization of 79 B. napus genotypes by calculating genetic distance based on sequence-related amplified polymorphism (SRAP) and genotyping by sequencing (GBS) in association with a neighbour-joining clustering algorithm. Despite the different genotypic analyses, neighbour-joining cluster analysis based on genetic distance of SRAP and GBS produced similar clusters. Homology between SRAP and GBS clusters was approximately 77 % when manually comparing clusters and 68 % when comparing clusters using Compare2Trees. This research demonstrates that SRAP can have similar efficacy when compared to next-generation sequencing technology for heterotic pool classification. This information may provide an important breeding scaffold for the development of hybrid cultivars based upon genetic distance and cluster analysis.     

Characterization of cross-bridge elasticity and kinetics of cross-bridge cycling during force development in single smooth muscle cells

Force development in smooth muscle, as in skeletal muscle, is believed to reflect recruitment of force-generating myosin cross-bridges. However, little is known about the events underlying cross-bridge recruitment as the muscle cell approaches peak isometric force and then enters a period of tension maintenance. In the present studies on single smooth muscle cells isolated from the toad (Bufo marinus) stomach muscularis, active muscle stiffness, calculated from the force response to small sinusoidal length changes (0.5% cell length, 250 Hz), was utilized to estimate the relative number of attached cross-bridges. By comparing stiffness during initial force development to stiffness during force redevelopment immediately after a quick release imposed at peak force, we propose that the instantaneous active stiffness of the cell reflects both a linearly elastic cross-bridge element having 1.5 times the compliance of the cross-bridge in frog skeletal muscle and a series elastic component having an exponential length-force relationship. At the onset of force development, the ratio of stiffness to force was 2.5 times greater than at peak isometric force. These data suggest that, upon activation, cross-bridges attach in at least two states (i.e., low-force-producing and high-force-producing) and redistribute to a steady state distribution at peak isometric force. The possibility that the cross-bridge cycling rate was modulated with time was also investigated by analyzing the time course of tension recovery to small, rapid step length changes (0.5% cell length in 2.5 ms) imposed during initial force development, at peak force, and after 15 s of tension maintenance. The rate of tension recovery slowed continuously throughout force development following activation and slowed further as force was maintained. Our results suggest that the kinetics of force production in smooth muscle may involve a redistribution of cross-bridge populations between two attached states and that the average cycling rate of these cross-bridges becomes slower with time during contraction.     

Alzheimer's associated variant ubiquitin causes inhibition of the 26S proteasome and chaperone expression

Intracellular protein inclusions in Alzheimer's disease and progressive supranuclear palsy contain UBB+1, a variant ubiquitin. UBB+1 is able block the 26S proteasome in cell lines. Proteasome inhibition by drug action has previously been shown to induce a heat-shock response and render protection against stress. We investigated UBB+1 by developing a stable, conditional expression model in SH-SY5Y human neuroblastoma cells. Induction of UBB+1 expression caused proteasome inhibition as was confirmed by reduced ability to process misfolded canavanyl proteins, accumulation of GFPu, a proteasome substrate, and reduced cleavage of a fluorogenic substrate. We show that expression of UBB+1 induces expression of heat-shock proteins. This priming of the chaperone system in these cells promotes a subsequent resistance to tert-butyl hydroperoxide-mediated oxidative stress. We conclude that although UBB+1-expressing cells have a compromised ubiquitin-proteasome system, they are protected against oxidative stress conditions.     

Ionic blockade of the rat connexin40 gap junction channel by large tetraalkylammonium ions.

The rat connexin40 gap junction channel is permeable to monovalent cations including tetramethylammonium and tetraethylammonium ions. Larger tetraalkyammonium (TAA(+)) ions beginning with tetrabutylammonium (TBA(+)) reduced KCl junctional currents disproportionately. Ionic blockade by tetrapentylammonium (TPeA(+)) and tetrahexylammonium (THxA(+)) ions were concentration- and voltage-dependent and occurred only when TAA(+) ions were on the same side as net K(+) efflux across the junction, indicative of block of the ionic permeation pathway. The voltage-dependent dissociation constants (K(m)(V(j))) were lower for THxA(+) than TPeA(+), consistent with steric effects within the pore. The K(m)-V(j) relationships for TPeA(+) and THxA(+) were fit with different reaction rate models for a symmetrical (homotypic) connexin gap junction channel and were described by either a one- or two-site model that assumed each ion traversed the entire V(j) field. Bilateral addition of TPeA(+) ions confirmed a common site of interaction within the pore that possessed identical K(m)(V(j)) values for cis-trans concentrations of TPeA(+) ions as indicated by the modeled I-V relations and rapid channel block that precluded unitary current measurements. The TAA(+) block of K(+) currents and bilateral TPeA(+) interactions did not alter V(j)-gating of Cx40 gap junctions. N-octyl-tributylammonium and -triethylammonium also blocked rCx40 channels with higher affinity and faster kinetics than TBA(+) or TPeA(+), indicative of a hydrophobic site within the pore near the site of block.     

Preparation, structure, solid state and gas phase stability of the mixed neodymium nitrate-chloride complex NdCl(NO3)2{[(MeO)2PO]2C(OH)Bu}2

The preparation and structure of the mixed anion complex NdCl(NO₃)₂{[(MeO)₂PO]₂C(OH)^tBu}₂ are reported. Single crystal X-ray diffraction shows that the bisphosphonate is bonded via both phosphoryl groups and the nitrates act as bidentate ligands. Intramolecular H-bonding is seen between the OH and the coordinated nitrate and chloride ligands. Thermal decomposition in the solid state is by loss of methyl nitrate. Electrospray mass spectrometry shows that loss of chloride is preferred over loss of nitrate in the gas phase. Attempted preparation of NdCl₂(NO₃){[(MeO)₂PO]₂C(OH)^tBu}₂ leads to the formation of a product approximating to [Nd{^tBu(OH)C(PO₃H₂)₂}₂]₂H · NO₃ · (PO₄H₂)₂. Electrospray mass spectrometry and elemental analysis confirm the presence of the [^tBu(OH)C(PO₄H₂)₂]⁻ in the decomposition products.