The building blocks for basolateral vesicles in polarized epithelial cells

After the discovery of basolateral sorting signals for polarized delivery in epithelial cells in the early 1990s, it was only about a decade later that the epithelial-cell-specific sorting adaptor AP-1B was discovered. AP-1B decodes a subclass of basolateral sorting signals and localizes to the recycling endosomes as opposed to the trans-Golgi network, suggesting that this is its major site of action. Furthermore, AP-1B does not simply select its cargo but also facilitates the recruitment of the exocyst complex needed for subsequent fusion with the plasma membrane. This review discusses our current knowledge of AP-1B function in cargo sorting to the basolateral membrane and its impact on our understanding of the similarities and differences between AP-1B-minus fibroblasts and AP-1B-positive epithelial cells.     

RNR1, a 3'-5' exoribonuclease belonging to the RNR superfamily, catalyzes 3' maturation of chloroplast ribosomal RNAs in Arabidopsis thaliana

Arabidopsis thaliana chloroplasts contain at least two 3′ to 5′ exoribonucleases, polynucleotide phosphorylase (PNPase) and an RNase R homolog (RNR1). PNPase has been implicated in both mRNA and 23S rRNA 3′ processing. However, the observed maturation defects do not affect chloroplast translation, suggesting that the overall role of PNPase in maturation of chloroplast rRNA is not essential. Here, we show that this role can be largely ascribed to RNR1, for which homozygous mutants germinate only on sucrose-containing media, and have white cotyledons and pale green rosette leaves. Accumulation of chloroplast-encoded mRNAs and tRNAs is unaffected in such mutants, suggesting that RNR1 activity is either unnecessary or redundant for their processing and turnover. However, accumulation of several chloroplast rRNA species is severely affected. High-resolution RNA gel blot analysis, and mapping of 5′ and 3′ ends, revealed that RNR1 is involved in the maturation of 23S, 16S and 5S rRNAs. The 3′ extensions of the accumulating 5S rRNA precursors can be efficiently removed in vitro by purified RNR1, consistent with this view. Our data suggest that decreased accumulation of mature chloroplast ribosomal RNAs leads to a reduction in the number of translating ribosomes, ultimately compromising chloroplast protein abundance and thus plant growth and development.     

Targeted proteomic analysis of 14-3-3 sigma, a p53 effector commonly silenced in cancer

To comprehensively identify proteins interacting with 14-3-3 sigma in vivo, tandem affinity purification and the multidimensional protein identification technology were combined to characterize 117 proteins associated with 14-3-3 sigma in human cells. The majority of identified proteins contained one or several phosphorylatable 14-3-3-binding sites indicating a potential direct interaction with 14-3-3 sigma. 25 proteins were not previously assigned to any function and were named SIP2-26 (for 14-3-3 sigma-interacting protein). Among the 92 interactors with known function were a number of proteins previously implicated in oncogenic signaling (APC, A-RAF, B-RAF, and c-RAF) and cell cycle regulation (AJUBA, c-TAK, PTOV-1, and WEE1). The largest functional classes comprised proteins involved in the regulation of cytoskeletal dynamics, polarity, adhesion, mitogenic signaling, and motility. Accordingly ectopic 14-3-3 sigma expression prevented cellular migration in a wounding assay and enhanced mitogen-activated protein kinase signaling. The functional diversity of the identified proteins indicates that induction of 14-3-3 sigma could allow p53 to affect numerous processes in addition to the previously characterized inhibitory effect on G2/M progression. The data suggest that the cancer-specific loss of 14-3-3 sigma expression by epigenetic silencing or p53 mutations contributes to cancer formation by multiple routes.     

Lysozyme Production as an Aid for Identification of Potentially Pathogenic Strains of Staphylococci

Lysozyme production is a frequent property of potentially pathogenic staphylococci. In the present study, 1,186 strains of human origin, 85 strains of animal origin, and 156 strains of Staphylococcus albus (epidermidis) were tested. Of 1,114 coagulase-positive strains of human and animal origin, 1,098 were lysozyme-positive (98.5%). On the other hand, of 157 coagulase-negative strains which, based on further investigations, belong to the potentially pathogenic staphylococci, all were lysozyme-positive. All of the 156 strains (100%) belonging to the species S. albus (epidermidis) were lysozyme-negative. We conclude that lysozyme production is a better index of potentially pathogenic staphylococci than the measurement of free coagulase, especially in cases of strains of animal origin. It is possible that lysozyme production allows a differentiation between pathogenic and nonpathogenic coagulase-negative staphylococci.     

Comparative morphology and evolution of the cnidosac in Cladobranchia (Gastropoda: Heterobranchia: Nudibranchia)

Background

A number of shelled and shell-less gastropods are known to use multiple defensive mechanisms, including internally generated or externally obtained biochemically active compounds and structures. Within Nudipleura, nudibranchs within Cladobranchia possess such a special defense: the ability to sequester cnidarian nematocysts – small capsules that can inject venom into the tissues of other organisms. This ability is distributed across roughly 600 species within Cladobranchia, and many questions still remain in regard to the comparative morphology and evolution of the cnidosac – the structure that houses sequestered nematocysts (called kleptocnides). In this paper, we describe cnidosac morphology across the main groups of Cladobranchia in which it occurs, and place variation in its structure in a phylogenetic context to better understand the evolution of nematocyst sequestration.

Results

Overall, we find that the length, size and structure of the entrance to the cnidosac varies more than expected based on previous work, as does the structure of the exit, the musculature surrounding the cnidosac, and the position and orientation of the kleptocnides. The sequestration of nematocysts has originated at least twice within Cladobranchia based on the phylogeny presented here using 94 taxa and 409 genes.

Conclusions

The cnidosac is not homologous to cnidosac-like structures found in Hancockiidae. Additionally, the presence of a sac at the distal end of the digestive gland may have originated prior to the sequestration of nematocysts. This study provides a more complete picture of variation in, and evolution of, morphological characters associated with nematocyst sequestration in Cladobranchia.

     

A tRNA's fate is decided at its 3′ end: Collaborative actions of CCA-adding enzyme and RNases involved in tRNA processing and degradation

tRNAs are key players in translation and are additionally involved in a wide range of distinct cellular processes. The vital importance of tRNAs becomes evident in numerous diseases that are linked to defective tRNA molecules. It is therefore not surprising that the structural intactness of tRNAs is continuously scrutinized and defective tRNAs are eliminated. In this process, erroneous tRNAs are tagged with single-stranded RNA sequences that are recognized by degrading exonucleases. Recent discoveries have revealed that the CCA-adding enzyme – actually responsible for the de novo synthesis of the 3′-CCA end – plays an indispensable role in tRNA quality control by incorporating a second CCA triplet that is recognized as a degradation tag. In this review, we give an update on the latest findings regarding tRNA quality control that turns out to represent an interplay of the CCA-adding enzyme and RNases involved in tRNA degradation and maturation. In particular, the RNase-induced turnover of the CCA end is now recognized as a trigger for the CCA-adding enzyme to repeatedly scrutinize the structural intactness of a tRNA. This article is part of a Special Issue entitled: SI: Regulation of tRNA synthesis and modification in physiological conditions and disease edited by Dr. Boguta Magdalena.     

Nitrogen distribution in young Norway spruce (Picea abies) trees as affected by pedospheric nitrogen supply

In numerous locations in Europe spruce trees are exposed to high loads of nitrogen. The present study was performed to characterize the distribution of nitrogen compounds under these conditions. For this purpose Norway spruce ( Picea abies [L.] Karst.) trees were cultivated under close-to-natural conditions of a forest understory in soil from an apparently nitrogen-limited field site in the Black Forest either with, or without supplementation of nitrogen as ammonium nitrate. After 11 and 20 months, growth, total nitrogen contents of the biomass, and total soluble non-proteinogenic nitrogen compounds (TSNN, i.e. nitrate, ammonium, soluble proteinogenic and non-proteinogenic amino compounds) in needles, xylem sap and phloem exudate were analysed. After 20 months of growth, N-fertilization had slightly enhanced the biomass of current-, but not of 1-year-old shoots. At both harvests, total N-content of 1-year-old needles was increased by N-fertilization, whereas current-year needles were not significantly affected. By contrast, TSNN was elevated by N-fertilization in both current-year and 1-year-old needles. The increase in TSNN was mainly attributed to an accumulation of arginine. Xylem sap analysis showed that the increase in TSNN of the needles was a consequence of enhanced nitrogen assimilation of the roots rather than the shoot. Since also TSNN in phloem exudates was enhanced, it appears that N-fertilization elevates the cycling pool of amino compounds in young Norway spruce trees. However, this pool seems to be subject to metabolic interconversion, since mainly glutamine and aspartate are transported in the xylem from the roots to the shoot, but arginine accumulated in the needles and the phloem.     

Pyridine nucleotide levels and activities of dehydrogenases in cambial derivatives ofRobinia pseudoacacia L.

Despite the importance of the vascular cambial differentiation, little is known about its regulation. In order to address this problem we attempted to biochemically characterize differentiating xylem and phloem elements during the early stages of development. By applying techniques of quantitative histochemistry we show that the total pool size of pyridine nucleotides is similar in the phloem (PD) and xylem (XD) oriented derivatives of the cambial zone of trees ofRobinia pseudoacacia L. Within the PD zone, the amount of NAD + NADH exceeded that of NADP + NADPH [around 600 versus 200 pmol (mg dry weight)^-1], possibly indicative of a preponderance of catabolic pathways (ratio of NADH∶NAD about 1). In contrast, the NADP(H) system dominated in the XD zone. This coincided with a high activity of NAD kinase. In addition, the extractable activities of the key enzymes of the oxidative pentose phosphate pathway, glucose-6-phosphate dehydrogenase and 6-phosphogluconate dehydrogenase, were greatly increased. At a ratio of NADPH∶NADP of approximately 1, this could be indicative of increased rates of reductive biosyntheses, and could thus well be involved in early steps of the formation of phenols and lignin monomers. Taken together, this first approach clearly shows that phloem-oriented and xylem-oriented cambial descendents exhibit distinct differences in their biochemical patterns even in early stages of differentiation.     

Conditions Affecting Song Acquisition in Nightingales (Luscinia megarhynchos L.)

Hand raised nightingales were alternatively confronted with different series of songs which permitted labeling of particular learning situations and allowed detection of specific consequences of diverse learning conditions. We found that visual contact with a tutor affected both quality and quantity of acquired patterns. Without visual contact the birds acquired only song sections consisting of repeated vocal units', which proved to be relevant for species recognition. With visual contact the birds learnt every presented song type completely (→ song type sharing between tutor and learner). Furthermore, the birds developed additional song types individually: by distinct parameter variation, or by recombination of particular tutor song units (Fig. 1; Table 1). Functional aspects of this type of song acquisition and development are discussed.