Skeletal biology in the toothless (osteopetrotic) rat

The toothless (tl) rat is a nonlethal osteopetrotic mutation characterized by the presence of few osteoclasts and the failure to be cured by bone-marrow transplantation. We examined the skeletal biology of tl rats and normal littermates up to 6 weeks after birth. Osteoclasts in tl rats were small, reduced 25-fold in number, and had greatly reduced concentrations of acid hydrolases. Bone shape internally and externally reflected reduced bone resorption, and tl rats were hypophosphatemic and mildly hypocalcemic at 2 weeks. These data indicate that the basic defect in tl rats is one of differentiation of osteoclasts and, coupled with the observation that normal bone-marrow cells cannot develop into osteoclasts in the tl skeleton, suggest that the defect lies in the skeletal micro-environment.     

Insertion Mutations in pilE Differentially Alter Gonococcal Pilin Antigenic Variation

Pilus antigenic variation in Neisseria gonorrhoeae occurs by the high-frequency, unidirectional transfer of DNA sequences from one of several silent pilin loci (pilS) into the expressed pilin gene (pilE), resulting in a change in the primary pilin protein sequence. Previously, we investigated the effects of large or small heterologous insertions in conserved and variable portions of a pilS copy on antigenic variation. We observed differential effects on pilin recombination by the various insertions, and the severity of the defect correlated with the disruption or displacement of a conserved pilin DNA sequence called cys2. In this study, we show that disruption or displacement of the pilE cys2 sequence by the same insertions or a deletion also affects pilin recombination. However, in contrast to the insertions in pilS, the analogous insertions in pilE impaired, but did not block, recombination of the flanking pilin sequences. These results, the change in the spectrum of donor silent copies used during variation, and our previous results with pilS mutations show that the donor pilS and recipient pilE play different roles in antigenic variation. We conclude that when high-frequency recombination mechanisms are blocked, alternative mechanisms are operative.     

Day vs. night predation on artificial caterpillars in primary rainforest habitats – an experimental approach

The influence of natural enemies has led to the evolution of various predator avoidance strategies in herbivorous insects. Many caterpillars are exclusively active at night and rest during the day. It is widely assumed that nocturnal activity in caterpillars reduces their risk of falling prey to their natural enemies. To test this hypothesis, we compared predation pressure between day and night in tree‐fall gaps and closed‐canopy forest sites in an Amazonian primary lowland rainforest. Artificial clay caterpillars, showing camouflaged colouration (green), were exposed as potential prey to a natural predator community. Attacks were significantly more frequent during daytime and were reduced by about a quarter at night in tree‐fall gaps, and by a third in closed‐canopy forest sites. This supports the idea of time‐dependent activity in caterpillars as an antipredatory adaptation. Further, independent of the time of day, predation pressure on caterpillars was significantly higher in tree‐fall gaps compared to closed‐canopy forest habitats. Nearly all predation events were caused by arthropods, whereas birds played a negligible role. Across both habitat types and time scales, ants acted as major predator group, emphasising their important role in population control of herbivorous insects in lowland rainforest ecosystems. This is the first experimental study using artificial caterpillars to examine whether time‐scheduling of exposition might influence predation risk amongst undefended, solitary, free‐living lepidopteran larvae.     

Comparison and confirmation of SNP-bud burst associations in European beech populations in Germany

European beech (Fagus sylvatica L.) is one of the most important forest tree species in Central Europe. Climate change scenarios predict an increase in annual mean temperatures that may cause earlier bud burst in spring, potentially leading to an increased late frost-risk. Despite the ecologic and economic importance of beech, knowledge about the molecular basis of bud burst is still scarce in this species. Here, an association analysis was used to detect SNPs that are significantly associated with beech bud burst. A translocation experiment was established with progenies of six different beech populations from three widely separated regions in Northeast, Central, and Southwest Germany. In total, 600 individuals of the translocation experiment were genotyped using a set of 46 SNPs located in bud burst candidate genes. The association analysis revealed seven SNPs significantly associated with bud burst, each SNP explaining only a few percent of the observed phenotypic variation. Since the same SNP set was used in a previous association analysis with European beech, we were able to compare and confirm significant associations between SNPs and bud burst in distinct beech populations growing in different environments.     

Volatile Organic Compounds in Uremia

Background

Although “uremic fetor” has long been felt to be diagnostic of renal failure, the compounds exhaled in uremia remain largely unknown so far. The present work investigates whether breath analysis by ion mobility spectrometry can be used for the identification of volatile organic compounds retained in uremia.

Methods

Breath analysis was performed in 28 adults with an eGFR ≥60 ml/min per 1.73 m², 26 adults with chronic renal failure corresponding to an eGFR of 10–59 ml/min per 1.73 m², and 28 adults with end-stage renal disease (ESRD) before and after a hemodialysis session. Breath analysis was performed by ion mobility spectrometryafter gas-chromatographic preseparation. Identification of the compounds of interest was performed by thermal desorption gas chromatography/mass spectrometry.

Results

Breath analyses revealed significant differences in the spectra of patients with and without renal failure. Thirteen compounds were chosen for further evaluation. Some compounds including hydroxyacetone, 3-hydroxy-2-butanone and ammonia accumulated with decreasing renal function and were eliminated by dialysis. The concentrations of these compounds allowed a significant differentiation between healthy, chronic renal failure with an eGFR of 10–59 ml/min, and ESRD (p<0.05 each). Other compounds including 4-heptanal, 4-heptanone, and 2-heptanone preferentially or exclusively occurred in patients undergoing hemodialysis.

Conclusion

Impairment of renal function induces a characteristic fingerprint of volatile compounds in the breath. The technique of ion mobility spectrometry can be used for the identification of lipophilic uremic retention molecules.     

Abscisic acid and water transport in sunflowers

The role of abscisic acid (ABA) in the transport of water and ions from the root to the shoot of sunflower plants (Helianthus annuus) was investigated by application of ABA either to the root medium or to the apical bud. The exudation at the hypocotyl stump of decapitated seedlings was measured with and without hydrostatic pressure (0–0.3 MPa) applied to the root. All ABA concentrations tested (10^-10–10^-4 mol·l^-1) promoted exudation. Maximal amounts of exudate (200% of control) were obtained with ABA at 10^-6·mol·l^-1 and an externally applied pressure of 0.1 MPa. The effect was rapid and long-lasting, and involved promotion of ion release to the xylem (during the first hours) as well as an increase in hydraulic conductivity. Abscisic acid applied to the apical bud had effects similar to those of the rootapplied hormone. Increased rates of exudation were also obtained after osmotic stress was applied to the root; this treatment increased the endogenous level of ABA in the root as well as in the shoot. Water potentials of the hypocotyls of intact plants increased when the roots were treated with ABA at 5°C, whereas stomatal resistances were lowered. The results are consistent with the view that ABA controls the water status of the plant not only by regulating stomatal transpiration, but also by regulating the hydraulic conductivity of the root.Abbreviations and symbols ABA abscisic acid - Tv volume flow - Lp hydraulic conductivity - PEG polyethyleneglycol - water potential - osmotic potential - osmotic value - P hydrostatic pressure     

Vertical stratification of a temperate forest caterpillar community in eastern North America

Vertical niche partitioning might be one of the main driving forces explaining the high diversity of forest ecosystems. However, the forest’s vertical dimension has received limited investigation, especially in temperate forests. Thus, our knowledge about how communities are vertically structured remains limited for temperate forest ecosystems. In this study, we investigated the vertical structuring of an arboreal caterpillar community in a temperate deciduous forest of eastern North America. Within a 0.2-ha forest stand, all deciduous trees ≥ 5 cm diameter at breast height (DBH) were felled and systematically searched for caterpillars. Sampled caterpillars were assigned to a specific stratum (i.e. understory, midstory, or canopy) depending on their vertical position and classified into feeding guild as either exposed feeders or shelter builders (i.e. leaf rollers, leaf tiers, webbers). In total, 3892 caterpillars representing 215 species of butterflies and moths were collected and identified. While stratum had no effect on caterpillar density, feeding guild composition changed significantly with shelter-building caterpillars becoming the dominant guild in the canopy. Species richness and diversity were found to be highest in the understory and midstory and declined strongly in the canopy. Family and species composition changed significantly among the strata; understory and canopy showed the lowest similarity. Food web analyses further revealed an increasing network specialization towards the canopy, caused by an increase in specialization of the caterpillar community. In summary, our study revealed a pronounced stratification of a temperate forest caterpillar community, unveiling a distinctly different assemblage of caterpillars dwelling in the canopy stratum.     

Regional differences in a nematoceran retina (Insecta,Diptera)

Summary The compound eye of Psychoda cinerea comprises two types of ommatidia, arranged so as to divide the retina into distinct dorsal and ventral regions. The P-type ommatidium, in the ventral part of the eye, differs fundamentally from the other dipteran ommatidia so far described, and is regarded as a primitive ommatidium. The acone dioptric apparatus is the same in both types, with a spherical lens and four Semper cells, the processes of which expand below the rhabdom to form a ring of pigment sacs. Only the distal region of the rhabdom is surrounded by a continuous ring of screening pigment, formed by 2 primary and 12–16 secondary pigment cells. The highly pigmented retinula cells penetrate the basement membrane proximally at about the level of their nuclei; in this region they are separated from the hemolymph by glial elements. The rhabdomeres R1–6 are fused to form a tube. The two types of ommatidia are defined by the arrangement of the retinula cells R7/8: in the T type the central rhabdomeres are one below the other, in the usual tandem position, whereas in the P type only R8 is central, with R7 in the peripheral ring. In the proximal region of the retina, retinula cells with parallel microvilli in neighboring ommatidia are joined in rows by lateral processes from the R8 cells. All the rhabdomeres are short and not twisted, which suggests that the retinula cells are highly sensitive to direction of polarization. The eye can adapt by a number of retinomotor processes. These findings, together with observations of behavior, imply that the psychodids have well-developed visual abilities.