Mitotic spindle: focus on the function of huntingtin

Mitotic spindle assembly and orientation are tightly regulated to allow the appropriate segregation of genetic material and cell fate determinants during symmetric and asymmetric divisions. Microtubules and many proteins including the dynein/dynactin complex and the large nuclear mitotic apparatus NuMA protein, are fundamental players in these mechanisms. A recent study reported that huntingtin regulates spindle orientation by ensuring the proper localization of the p150(Glued) subunit of dynactin, dynein and NuMA. This function of huntingtin is conserved in Drosophila. Among other events, spindle orientation influences the fate of daughter cells. In agreement with this, huntingtin changes the direction of division of mouse cortical progenitors and promotes neurogenesis in the neocortex. We will also discuss the involvement of mitotic spindle components in neuronal disorders.     

Where to sleep in a rural landscape? A comparative study of resting sites pattern in two syntopic Martes species

The niche‐complementarity hypothesis predicts that two sympatric species must differ in their requirements for one of the three main ecological dimensions (i.e. habitat use, diet, and activity time) to coexist. European pine marten Martes martes and stone marten M. foina are syntopic medium‐sized mustelids with very similar morphology and ecology for which resting sites are a key resource. To better understand how these species coexist, we investigated whether key features of their resting site pattern (number of resting sites, area over which they are distributed, main habitat type used for resting) differed. We used diurnal telemetry to identify resident individuals (e.g. spatially stable individuals over time) and to locate them during resting periods in a fragmented forested area in France. Stone marten used fewer resting sites distributed over a smaller surface area than pine marten. Most stone marten resting sites were located in open habitat (83%) in the proximity of human habitations, whereas pine martens rested almost exclusively in forest (98%). Sex, age, and season explained some variability in both the number of resting sites and the probability of resting within forested habitat for stone marten but not pine marten. The area covered by resting sites was larger in males than in females, but age modulated this difference in an opposite way for the two species. Such a pattern was expected given the intra‐sexual territoriality and the reproductive phenology of these species. Overall, stone marten showed higher inter‐individual variability in resting site pattern than pine marten. The particular pattern observed in subadult male stone martens during summer (increase in resting site surface area and in the probability to rest in forest) may reflect an attempt to settle in forests, and we discuss these implications in the context of interspecific competition.     

The genome of the non-cultured,bacterial-like organism associated with citrus greening disease contains thenusG-rplKAJL-rpoBC gene cluster and the gene for a bacteriophage type DNA polymerase

We have recently cloned three DNA fragments (In-2.6, In-1.0, and In-0.6) of the noncultured, bacterial-like organism (BLO) associated with citrus greening disease. Nucleotide sequence determination has shown that fragment In-2.6 is part of therplKAJL-rpoBC gene cluster, a well-known operon in eubacteria. The DNA fragment upstream of and partially overlapping with In-2.6 could be isolated and was shown to be thenusG gene. InEscherichia coli, nusG is also immediately upstream ofrplKAJL-rpoBC. Fragment In-1.0 carries the gene for a bacteriophage type DNA polymerase. Fragment In-0.6 could not be identified.When In-2.6 was used, at high stringency, as a probe to detect greening BLO strains in infected plants, hybridization was obtained with all Asian strains tested, but not with the African strain examined. At lower stringencies, In-2.6 was able to detect also the African strain. The implications of these reults in the taxonomical position of the greening BLO are discussed.     

Assay of microsomal oxysterol 7α-hydroxylase activity in the hamster liver by a sensitive method: in vitro modulation by oxysterols

A method of assaying hepatic cytochrome P-450, oxysterol 7α-hydroxylase (CYP7B), was developed by combining the use of 25-[26,27-³H]hydroxycholesterol as a substrate and hydroxypropyl-β-cyclodextrin as a substrate vehicle. When these assay conditions were tested, an undesirable transformation was observed of the reaction product, 7α,25-dihydroxycholesterol, into 3-oxo-7α,25-dihydroxy-4-cholesten by the activity of 3β-hydroxy-Δ⁵-C₂₇ steroid oxydoreductase, a microsomal NAD⁺ and NADP⁺ dependent enzyme of bile acid metabolism. A great improvement was reached by using a continuous NADPH generating system which constantly re-transforms NADP⁺ into NADPH, thus inhibiting this activity. This improved CYP7B assay, comparable to our previously described assay for cholesterol 7α-hydroxylase (CYP7A), allowed a 3-fold increase of the apparent enzyme activity. The possibility to simultaneously measure CYP7A and CYP7B activities on the same microsomal preparation was investigated. A marked decrease (?33%) in the CYP7B activity was noticed, while that of CYP7A remained unchanged. The CYP7B activity was observed to be inhibited by cholesterol (?30%) and also by the oxysterols 7α-hydroxycholesterol (?21%), 7β-hydroxycholesterol (?25%) and epicoprostanol (?20%), and by cyclosporin A (?26%). It can be concluded that this sensible and easy to perform CYP7B assay allows to observe, at least in vitro, a modulation of the enzyme activity by oxysterols.     

Male hypofertility induced by Paraquat consumption in the non-target parasitoid Anisopteromalus calandrae (Hymenoptera: Pteromalidae)

The effects of a herbicide – Paraquat – on male development and reproduction were tested on the parasitoid wasp Anisopteromalus calandrae (Hymenoptera, Pteromalidae) by injecting host larvae with different concentrations of this substance. Data measured were: (1) developmental success, (2) sperm stock in seminal vesicles, (3) ability to copulate and transfer sperm, and (4) offspring production. Both developmental success and sperm in seminal vesicles were reduced in the “Paraquat” groups. However, neither sperm stored in the females’ spermatheca, nor offspring production (number of female offspring and sex ratio) differed from controls, whatever the host treatment. The decreased of male sperm reserve in ‘‘Paraquat” group is likely to reduce their reproductive success because they can succefully inseminated less female than control males. These males are thus hyporfertiles. Because Paraquat has non-negligible consequences on non-target parasitoid males, it is likely to affect natural and controlled insect populations.     

Use of near-infrared reflectance spectroscopy to predict the percentage of dead versus living grass roots

Plant and Soil - We tested the potential of near-infrared reflectance spectroscopy (NIRS) to predict the percentage of dead versus living roots of five grass species grown in monocultures under...     

Salicylic Acid Transport in Ricinus communis Involves a pH-Dependent Carrier System in Addition to Diffusion

Despite its important functions in plant physiology and defense, the membrane transport mechanism of salicylic acid (SA) is poorly documented due to the general assumption that SA is taken up by plant cells via the ion trap mechanism. Using Ricinus communis seedlings and modeling tools (ACD LogD and Vega ZZ softwares), we show that phloem accumulation of SA and hydroxylated analogs is completely uncorrelated with the physicochemical parameters suitable for diffusion (number of hydrogen bond donors, polar surface area, and, especially, LogD values at apoplastic pHs and Δ LogD between apoplast and phloem sap pH values). These and other data (such as accumulation in phloem sap of the poorly permeant dissociated form of monohalogen derivatives from apoplast and inhibition of SA transport by the thiol reagent p-chloromercuribenzenesulfonic acid [pCMBS]) lead to the following conclusions. As in intestinal cells, SA transport in Ricinus involves a pH-dependent carrier system sensitive to pCMBS; this carrier can translocate monohalogen analogs in the anionic form; the efficiency of phloem transport of hydroxylated benzoic acid derivatives is tightly dependent on the position of the hydroxyl group on the aromatic ring (SA corresponds to the optimal position) but moderately affected by halogen addition in position 5, which is known to increase plant defense. Furthermore, combining time-course experiments and pCMBS used as a tool, we give information about the localization of the SA carrier. SA uptake by epidermal cells (i.e. the step preceding the symplastic transport to veins) insensitive to pCMBS occurs via the ion-trap mechanism, whereas apoplastic vein loading involves a carrier-mediated mechanism (which is targeted by pCMBS) in addition to diffusion.