Birch leaves as a resource for herbivores: Seasonal occurrence of increased resistance in foliage after mechanical damage of adjacent leaves

Summary Seasonal occurrence of such wound-induced reaction in birch foliage which deteriorates the quality of nearby leaves for herbivores was tested by means of bioassays. Length of the larval period was protracted in two early and mid-summer (larval period!) lepidopteran species as well as in two mid-summer hymenopteran species when larvae were reared on birch leaves whose adjacent leaves had earlier been damaged mechanically. This response was not found for two late-summer hymenopteran species. In a lepidopteran species whose larval period lasts through the whole season, retardation in growth was significant in the beginning of August but notl later. Hence such response of leaves, interpreted as defensive on the part of the birch, was not efficient after leaves had gained their final size. The potential consequences of wound-induced responses of leaves for herbivores are discussed.     

Higher nest predation risk in association with a top predator: mesopredator attraction?

Breeding close to top predators is a widespread reproductive strategy. Breeding animals may gain indirect benefits if proximity to top predators results in a reduction of predation due to suppression of mesopredators. We tested if passerine birds gain protection from mesopredators by nesting within territories of a top predator, the Ural owl (Strix uralensis). We placed nest boxes for pied flycatchers (Ficedula hypoleuca) in Ural owl nest sites and in control sites (currently unoccupied by owls). The nest boxes were designed so that nest predation risk could be altered (experimentally increased) after flycatcher settlement; we considered predation rate as a proxy of mesopredator abundance. Overall, we found higher nest predation rates in treatment than in control sites. Flycatcher laying date did not differ between sites, but smaller clutches were laid in treatment sites compared to controls, suggesting a response to perceived predation risk. Relative nest predation rate varied between years, being higher in owl nest sites in 2 years but similar in another; this variation might be indirectly influenced by vole abundance. Proximity to Ural owl nests might represent a risky habitat for passerines. High predation rates within owl territories could be because small mesopredators that do not directly threaten owl nests are attracted to owl nest sites. This could be explained if some mesopredators use owl territories to gain protection from their own predators, or if top predators and mesopredators independently seek similar habitats.     

Relation of chronotype to sleep complaints in the general Finnish population

Individuals show variation in their preference for the daily timing of activities. In this study the authors analyzed whether chronotypes associate with sleep duration and sleep-related complaints. The authors used the National FINRISK Study 2007 Survey data on 3696 women and 3162 men, representative of the Finnish population aged 25 yrs and older, for the assessment of chronotype and self-reported sleep. Evening types experienced insomnia symptoms, had nightmares, and had used recently hypnotics significantly more often than other chronotypes among both men and women. In a multinominal logistic regression model predicting insufficient sleep, the association of eveningness with insufficient sleep was not abolished after adjustment for sex, age, and sleep duration. The prevalence of short sleepers was significantly higher in evening types among men than among women, whereas that of long sleepers was significantly higher in evening types among both men and women, as compared with the other chronotypes. These results indicate that eveningness predisposes individuals to a range of sleep complaints.     

Solution structures of the first and fourth TSR domains of F-spondin

F-spondin is a protein mainly associated with neuronal development. It attaches to the extracellular matrix and acts in the axon guidance of the developing nervous system. F-spondin consists of eight domains, six of which are TSR domains. The TSR domain family binds a wide range of targets. Here we present the NMR solution structures of TSR1 and TSR4. TSR domains have an unusual fold that is characterized by a long, nonglobular shape, consisting of two beta-strands and one irregular extended strand. Three disulfide bridges and stack of alternating tryptophan and arginine side-chains stabilize the structure. TSR1 and TSR4 structures are similar to each other and to the previously determined TSR domain X-ray structures from another protein, TSP, although TSR4 exhibits a mobile loop not seen in other structures.     

Development of a denaturation/renaturation-based production process for ferritin nanoparticles

Recently, we presented a simple method for generating biological functional protein-based nanoparticles that are ready for use as label agents in bioaffinity assays (J??skel?inen et al., 2007 Small 3:1362-1367). In this process, the particle shell (ferritin protein) and binding molecules are conjugated via genetic fusion, and particles with binding capacity are produced in a single bacterial cultivation. Production is combined with simple, non-chromatographic purification during which Europium ions are introduced into particles to serve as marker agents. Denaturation-refolding has previously performed by means of pH changes. Here, we test urea as an alternative agent for denaturation, and examine techniques to improve refolding of the functional particles. Three different types of binding molecules were employed in our experiments: biotin carboxyl carrier protein (a small protein with 87 amino acids), single chain antibody fragment (a complex binding protein) and calmodulin-binding peptide (27 amino acids). Urea was successfully utilized to generate functional particles with inherent binding activity and label function. Additionally, particle yield was effectively optimized by analyzing various refolding and bacterial production conditions. Our results clearly demonstrate that this simple biological method of producing functional ferritin-based particles is flexible, and different types of binding moieties can be applied by adjusting the production conditions.     

Horseradish peroxidase-catalyzed oxidation of chlorophyll a with hydrogen peroxide: Characterization of the products and mechanism of the reaction

Horseradish peroxidase was verified to catalyze, without any phenol, the hydrogen peroxide oxidation of chlorophyll a (Chl a), solubilized with Triton X-100. The 13²(S) and 13²(R) diastereomers of 13²-hydroxyChl a were characterized as major oxidation products (ca. 60%) by TLC on sucrose, UV-vis, ¹H, and ¹³C NMR spectra, as well as fast-atom bombardment MS. A minor amount of the 15²-methyl, 17³-phytyl ester of Mg-unstable chlorin was identified on the basis of its UV-vis spectrum and reactivity with diazomethane, which converted it to the 13¹,15²-dimethyl, 17³-phytyl ester of Mg-purpurin 7. The side products (ca. 10%) were suggested to include the 17³-phytyl ester of Mg-purpurin 18, which is known to form easily from the Mg-unstable chlorin. The side products also included two red components with UV-vis spectral features resembling those of pure Chl a enolate anion. Hence, the two red components were assigned to the enolate anions of Chl a and pheophytin a or, alternatively, two different complexes of the Chl a enolate ion with Triton X-100. All the above products characterized by us are included in our published free-radical allomerization mechanism of Chl a, i.e. oxidation by ground-state dioxygen. The HRP clearly accelerated the allomerization process, but it did not produce bilins, that is, open-chain tetrapyrroles, the formation of which would require oxygenolysis of the chlorin macrocycle. In this regard, our results are in discrepancy with the claim by several researchers that ‘bilirubin-like compounds’ are formed in the HRP-catalyzed oxidation of Chl a. Inspection of the likely reactions that occurred on the distal side of the heme in the active centre of HRP provided a reasonable explanation for the observed catalytic effect of the HRP on the allomerization of Chl. In the active centre of HRP, the imidazole nitrogen of His-42 was considered to play a crucial role in the C-13² deprotonation of Chl a, which resulted in the Chl a enolate ion resonance hybrid. The Chl enolate was then oxidized to the Chl 13²-radical while the HRP Compound I was reduced to Compound II. The same reactive Chl derivatives, i.e. the Chl enolate anion and the Chl 13²-radical, which are produced twice in the HRP reaction cycle, happen to be the crucial intermediates in the initial stages of the Chl allomerization mechanism.     

The predation risks of interspecific eavesdropping: weasel–vole interactions

Competing species benefit from eavesdropping on each other's signals by learning about shared resources or predators. But conspicuous signals are also open to exploitation by eavesdropping predators and should also pose a threat to other sympatric prey species. In western Finland, sibling voles Microtus rossiameridionalis and field voles M. agrestis compete for food and space, and both species rely upon scent marks for intraspecific communication. Both vole species are prey to a range of terrestrial scent hunting predators such as least weasels, however, the competitively superior sibling voles are taken preferentially. We tested in large out‐door enclosures whether field voles eavesdrop on the signals of its competitor, and whether they behave as though this eavesdropping carries a risk of predation. We presented field voles with scent marks from unknown conspecifics and sibling voles and measured their visitation, activity and scent marking behaviours at these scents under high (weasel present) and low (weasel absent) predation risk. Field voles readily visited both field and sibling vole scents under both high and low predation risk; however their activity at sibling vole scent marks declined significantly under increased predation risk. In contrast, predation risk did not affect field voles’ activity at conspecific scents. Thus, field voles were compelled to maintain eavesdropping on heterospecific scents under an increased risk of predation, however they compensated for this additional risk by reducing their activity at these risky scents. Scent marking rates declined significantly under high predation risk. Our results therefore reveal a hidden complexity in the use of social signals within multi‐species assemblages that is clearly sensitive to the potential for increased predation risk. The predation risks of interspecific eavesdropping demonstrated here represents a significant generalisation of the concept of associational susceptibility.     

Targeting of drugs and nanoparticles to tumors

The various types of cells that comprise the tumor mass all carry molecular markers that are not expressed or are expressed at much lower levels in normal cells. These differentially expressed molecules can be used as docking sites to concentrate drug conjugates and nanoparticles at tumors. Specific markers in tumor vessels are particularly well suited for targeting because molecules at the surface of blood vessels are readily accessible to circulating compounds. The increased concentration of a drug in the site of disease made possible by targeted delivery can be used to increase efficacy, reduce side effects, or achieve some of both. We review the recent advances in this delivery approach with a focus on the use of molecular markers of tumor vasculature as the primary target and nanoparticles as the delivery vehicle.

Introduction

The concept of targeted drug delivery is attractive because it recapitulates some of the advantages of topical application of drugs: high local concentration and low systemic exposure. In practice, this approach has met with some success but has not provided the hoped-for “silver bullets.” However, recent developments in the field have rekindled interest in the targeting approach. We call this mode of drug delivery “synaphic” targeting; it is also referred to as pathotropic or active targeting. Cancer stands out as a disease most likely to benefit from targeted drug delivery. Tumor cells express many molecules on their surface that distinguish them from normal cells. Traditionally, such molecules were detected with antibodies, but screening of peptide and aptamer libraries has greatly expanded the number of tools available for selective binding to tumor cells (for reviews see Ruoslahti, 2002; Peer et al., 2007). Leukemia and lymphoma treatments with antibodies conjugated to a radioisotope have been in clinical use for several years (Sharkey and Goldenberg, 2005). However, this approach has not been as successful with solid tumors. The apparent reason is the difficulty in delivering drugs into these tumors; drugs only penetrate a few cell diameters into the extravascular tumor tissue from blood vessels (Hambley and Hait, 2009). This low penetration appears to arise from two main factors: first, tumor vessels are poorly perfused with blood and are dysfunctional, which limits the delivery of blood-borne compounds to tumors (Jain, 1999). Second, tumors have a high interstitial pressure thought to result from dysfunctional lymphatics, which causes tissue fluid to flow out of the tumor, working against diffusion of drugs from the blood vessels into the tumor (Jain, 1999; Heldin et al., 2004). The leakiness of tumor vessels partially makes up for the poor penetration (the so-called enhanced permeability and retention [EPR] effect), but EPR is not very effective, and its size dependency and variability from tumor to tumor limit its usefulness (Maeda et al., 2000; Iyer et al., 2006; Sugahara et al., 2009). Interstitial fibrosis can further retard the diffusion of compounds through tumors (Olive et al., 2009). Targeting treatments to selective markers in tumor vessels does not suffer from some of these drawbacks of targeting tumor cells; in particular, no tissue penetration is required for the compound to reach its target. The luminal side of tumor vessels is fully accessible to compounds circulating in the blood, and the vessels can serve as a gateway to the tumor interior for compounds concentrated in the vessels. Using a targeting probe with tumor-penetrating properties and a receptor that is shared between tumor vessels and tumor cells provides additional advantages (Fig. 1). Thus, we have chosen to focus this review on targeting approaches that make use of specific markers in tumor vessels. We will also discuss solutions to the poor penetration of compounds into tumor tissue and the roles that nanoparticles can play in targeted therapies.Open in a separate windowFigure 1.Synaphic targeting of tumors. The targeted receptors can be on tumor cells, tumor vessels, or shared by both. (A) Probes that recognize solely tumor cells provide little improvement of tumor accumulation over a nontargeted probe. (B) Probes that recognize tumor vessels accumulate in the tumor, but entry into tumor tissue relies on passive mechanisms. (C) Probes that recognize both the vessels and tumor cells combine the (limited) efficiency of the two targeting mechanisms. (D) Tumor-penetrating targeting probes (so far only peptides with such characteristics are known) provide a particularly potent targeting system.

Molecular signatures in tumor vessels

Distinct features of tumor vessels.

Tumor blood vessels are distinct from normal vessels. In addition to being tortuous, uneven in diameter, and leaky, tumor vessels express various cell surface and extracellular matrix proteins that normal vessels do not express or do so at much lower levels than tumor vessels (for review see Ruoslahti, 2002). The expression of many of these proteins in tumor vessels is associated with angiogenesis, and they are often functionally important in that process (Hanahan and Folkman, 1996; Alitalo and Carmeliet, 2002). Tumors also contain lymphatic vessels, and many tumors produce growth factors that stimulate lymphangiogenesis (Karpanen and Alitalo, 2008). Lymphatics are not necessary for tumor growth but are important conduits of metastasis. Like tumor blood vessels, tumor lymphatics can also express specific molecular markers.

Screening for markers in tumor vasculature.

Screening of phage-displayed peptide libraries, particularly when performed in vivo, has provided a very useful discovery tool for vascular markers in tumor vessels and elsewhere (Pasqualini and Ruoslahti, 1996). A major advantage of the in vivo phage screening is that it is unbiased in revealing what works in vivo. Other unbiased methods, such as antibody-based screens (Jacobson et al., 1996), cloning strategies (Carson-Walter et al., 2001), and in vivo biotinylation (Borgia et al., 2010), have also been used successfully in analyzing tumor vasculature. Phage screening has uncovered a large number of tumor-homing peptides that have been used to identify the corresponding binding protein (receptor). An early study on tumor-homing peptides (Arap et al., 1998) validated the method by producing tumor-homing peptides with RGD (arginine/glycine/aspartice acid) and NGR (asparagine/glycine/arginine) motifs, which had been previously identified in screens for integrin-binding peptides performed in vitro. F3 is an example of a novel tumor-homing peptide identified by in vivo phage screening (Porkka et al., 2002). F3 binds to nucleolin, which is ubiquitous as an intracellular protein but is expressed at the cell surface of endothelial cells and tumor cells in vivo (Christian et al., 2003). In vitro, all cells seem to be positive for cell surface nucleolin (Borer et al., 1989; Bonnet et al., 1996) presumably because cultured cells resemble cells that have been activated in vivo. Cell surface nucleolin is an angiogenesis marker that is both a suitable target for drug delivery (Christian et al., 2001; Reddy et al., 2006; Henke et al., 2008; Drecoll et al., 2009) and involved in the angiogenesis process (Fogal et al., 2009). The in vivo screening of phage libraries has also produced several potent tumor-homing peptides, the target molecules of which remain to be identified (Hoffman et al., 2003; Joyce et al., 2003; Järvinen and Ruoslahti, 2007; Chang et al., 2009).The expression of intracellular proteins such as nucleolin at the cell surface of tumor cells and tumor endothelial cells appears to be a general principle. Phage display is particularly well suited for the discovery of such markers because the method inherently relies on binding to accessible targets on the cell surface rather than overall expression levels. In vivo cell surface labeling followed by monoclonal antibody production and proteomics analyses is another way of interrogating the cell surface. In addition to aforementioned nucleolin, the cytoplasmic proteins annexin1 (Oh et al., 2004) and plectin-1 (Kelly et al., 2008) have been found to be present at the cell surface of endothelial cells in tumors but not in normal tissues. Another example is p32 protein (gC1q receptor, hyaluronic acid–binding protein). This protein is primarily a mitochondrial protein, but it is also expressed at the cell surface of lymphatic, myeloid, and cancer cells in tumors but not in normal tissues (Fogal et al., 2008). This protein is the receptor for the tumor-homing peptide LyP-1, originally discovered using in vivo phage display (Laakkonen et al., 2002).

Adhesion receptors as angiogenesis markers.

Some of the molecular markers in tumor vasculature have been found by studying the expression of known cell surface receptors in tumor vessels. A prime example is the overexpression of αvβ3 and αvβ5 integrins in angiogenic vessels (Brooks et al., 1994; Erdreich-Epstein et al., 2000; Desgrosellier and Cheresh, 2010). These integrins are prime targets for synaphic drug delivery. Vascular markers expressed on the surface of the endothelium, such as the integrins, are most readily available for the binding of blood-borne compounds. However, the ECM also contains distinct markers that can be used in tumor targeting. An alternatively spliced form of fibronectin containing an additional type III domain, ED-B, is selectively expressed in tumor (and other) angiogenic vessels (Nilsson et al., 2001). Antibodies to ED-B have been used to construct immunotoxins and other compounds for tumor targeting. Proteolytically processed type IV collagen is another matrix component that can be detected with antibodies or peptides (Roth et al., 2006; Mueller et al., 2009). The support cells (mural cells) in the vascular wall also contain markers that are specific for tumor vessels and that can be potentially useful in tumor targeting. NG2, a membrane-spanning chondroitin sulfate proteoglycan, is a cell surface marker of pericytes (and smooth muscle cells) in angiogenic vessels not expressed in the pericytes of normal vessels (Stallcup and Huang, 2008). One of the PDFG receptors is another marker that is expressed at high levels in pericytes (Song et al., 2005).

Fibrin–fibronectin complexes in tumors.

Peptides that specifically bind to fibrin–fibronectin complexes or other proteins associated with these complexes also home to tumors. The walls of tumor vessels and the interstitial spaces in tumors contain products of blood clotting, presumably as a result of plasma protein seepage from leaky tumor vessels. Leaked fibrinogen is converted to a fibrin meshwork by tissue-procoagulant proteins such as tissue factor (Dvorak et al., 1985; Abe et al., 1999; Pilch et al., 2006). Other plasma proteins, plasma fibronectin in particular, become covalently linked or otherwise bound to the fibrin meshwork. These fibrin–fibronectin complexes in the walls of tumor vessels and in the tumor interstitial stroma can be accessed with peptides derived from phage screening, such as the nine–amino acid cyclic peptide CLT-1 (Pilch et al., 2006; Ye et al., 2008) and the pentapeptide CREKA (Simberg et al., 2007). Fibrin-binding peptides isolated for the purpose of targeting blood clots in cardiovascular disease would presumably behave similarly if tested for tumor homing. The CREKA peptide has been used to confer a new function to nanoparticles: self-amplification of tumor homing (see Amplified tumor homing; Simberg et al., 2007).

Tumor endothelial markers (TEMs).

Surveying mRNA expression by the serial analysis of gene expression technique has revealed a large number of striking differences between endothelial cells isolated from human colon cancers and those from adjacent normal tissue (Carson-Walter et al., 2001). Among these TEMs are collagens, some of which are expressed at strikingly high levels in tumor endothelial cells, at least at the mRNA level. The high collagen expression may relate to the extensive fibrosis found in many tumors and recently shown to contribute to the poor penetration of drugs into tumors (Olive et al., 2009). Perhaps the most interesting among the TEMs is TEM 8, which is one of the two receptors for the anthrax toxin (Nanda et al., 2004). An effort is under way to develop anthrax toxin variants that bind only to TEM 8 and that could be used to target tumor vasculature for destruction.

Second cancers following the diagnosis of Merkel cell carcinoma: A nationwide cohort study

Merkel cell carcinoma (MCC) is a rare neuroendocrine carcinoma of the skin. MCCs and some other skin cancers, such as basal cell carcinomas, frequently harbour Merkel cell polyomavirus DNA. The purpose of the study was to investigate the frequency of second cancers following the diagnosis of MCC. We studied the incidence of second primary cancers after the diagnosis of MCC from the files of the Finnish Cancer Registry in 1979–2006. Among the 172 MCC patients identified a total of 34 second primary cancers were detected in 30 individuals after the diagnosis of MCC. Female MCC patients were diagnosed with 25 subsequent cancers (SIR, 2.35; 95% CI, 1.52–3.47; p < 0.001) and male patients with 9 cancers (SIR, 2.32, 95% CI, 1.06–4.40; p < 0.05). The MCC patients had an increased risk for a subsequent cancer (any site) compared to age-, gender- and calendar period-matched general population (standardized incidence ratio [SIR] 2.34; 95% confidence interval [CI], 1.62–3.27). The risks for basal cell carcinoma of the skin (O = 11), SIR, 3.48; 95% CI, 1.74–6.22 and chronic lymphocytic leukemia (O = 2), SIR, 17.9; 95% CI, 2.16–64.6 were significantly elevated. The SIRs for an overall second primary cancer risk did not change markedly with time since the diagnosis of MCC. We conclude that patients diagnosed with MCC have an increased risk for a second cancer. This risk may in part result from shared etiological factors between MCC and other tumour types, such as immunosuppression or possibly Merkel cell polyomavirus infection.     

Efficient regeneration of fertile barley plants from callus cultures of several Nordic cultivars

The regeneration potential of three major Estonian barley cultivars was tested and compared to that of the Finnish cultivar Kymppi. Two different regeneration systems were used. The first was characterized by the high maltose concentration (60 g l(-1)) and by the use of 2,4D together with two different combinations of amino acids in the callus induction medium followed by the regeneration medium containing BAP (2 mg l(-1)) and 2,4D (0.2 mg l(-1)). The second exploited callus induction medium that contained Dicamba, lower concentrations of maltose (30 g l(-1)) and higher concentrations of myo-inositol and thiamine and different set of amino acids and regeneration medium that contained higher concentrations of Cu2+ and inorganic nitrogen accompanied by lower concentrations of NH4+ and BAP, when compared to the first regeneration system. The second regeneration system used produced significantly higher rates of callus induction, callus growth and regeneration of plantlets. However, it yielded also many albino plants (up to 51%), whereas the first regeneration system used did not produce practically any albino plants. No major genotype-dependent differences were observed in comparison between two regeneration systems - in both systems higher regeneration potential of Anni, Elo and Kymppi contradicted to the low regeneration potential of Teele. It is concluded that the continuous somatic embryogenesis on the regeneration medium allows the regeneration of many plants from the same callus over long periods of time and makes available highly efficient regeneration protocols for Estonian and Finnish barley cultivars.