Co‐encapsulation of anti‐BCR‐ABL siRNA and imatinib mesylate in transferrin receptor‐targeted sterically stabilized liposomes for chronic myeloid leukemia treatment

Chronic myeloid leukemia (CML) is triggered by the BCR‐ABL oncogene. Imatinib is the first‐line treatment of CML; however imatinib resistance and intolerance have been detected in many patients. Therefore, new therapeutic approaches are required. The present work aimed at the development and application of transferrin receptor (TrfR) targeted liposomes co‐encapsulating anti‐BCR‐ABL siRNA and imatinib at different molar ratios. The encapsulation yields and drug loading of each molecule was evaluated. Anti‐leukemia activity of the developed formulations co‐encapsulating siRNA and imatinib and of the combination of Trf‐liposomes carrying siRNA and free imatinib under two different treatment schedules of pre‐sensitization was assessed. The results obtained demonstrate that the presence of imatinib significantly decreases the encapsulation yields of siRNA, whereas imatinib encapsulation yields are increased by the presence of siRNA. Cytotoxicity assays demonstrate that the formulations co‐encapsulating siRNA and imatinib promote a 3.84‐fold reduction on the imatinib IC₅₀ (from 3.49 to 0.91 µM), whereas a 8.71‐fold reduction was observed for the pre‐sensitization protocols (from 42.7 to 4.9 nM). It was also observed that the formulations with higher siRNA to imatinib molar ratios promote higher cell toxicity. Thus, the present work describes a novel triple targeting strategy with one single system: cellular targeting (through the targeting ligand, transferrin) and molecular targeting at the BCR‐ABL mRNA and Bcr‐Abl protein level. Biotechnol. Bioeng. 2010;107: 884–893. © 2010 Wiley Periodicals, Inc.     

First confirmed case of pseudocopulation in terrestrial orchids of South America: Pollination of Geoblasta pennicillata (Orchidaceae) by Campsomeris bistrimacula (Hymenoptera, Scoliidae)

The attraction of male pollinating insects by sexual deception is known for several orchids from the Mediterranean, Australia, South Africa and South America. The sexual delusion may be so enticing in some species that it elicits males to attempt copulation with insect-like structures of the labellum. Pollination by such a pseudocopulation mechanism is reported here for the terrestrial orchid Geoblasta penicillata (Chloraeinae) from subtropical South America. Observations of the pollination process were carried out in two wild populations 560 km distant from each other. The only pollinators seen in both populations were male Campsomeris bistrimacula (Scoliidae) wasps. They attempted copulation with the insect-like labellum by directing the genitalia to its base whereby pollinia got attached to the dorsal surface of the metasoma. The present case of pseudocopulation, which is in South America the second known and the first recorded in wild populations, represents a striking parallel to the Australian Calochilus campestris also pollinated by male scoliid wasp of the genus Campsomeris.     

Calcium-dependent and -independent interactions of the S100 protein family

The S100 proteins comprise at least 25 members, forming the largest group of EF-hand signalling proteins in humans. Although the proteins are expressed in many tissues, each S100 protein has generally been shown to have a preference for expression in one particular tissue or cell type. Three-dimensional structures of several S100 family members have shown that the proteins assume a dimeric structure consisting of two EF-hand motifs per monomer. Calcium binding to these S100 proteins, with the exception of S100A10, results in an approx. 40 degrees alteration in the position of helix III, exposing a broad hydrophobic surface that enables the S100 proteins to interact with a variety of target proteins. More than 90 potential target proteins have been documented for the S100 proteins, including the cytoskeletal proteins tubulin, glial fibrillary acidic protein and F-actin, which have been identified mostly from in vitro experiments. In the last 5 years, efforts have concentrated on quantifying the protein interactions of the S100 proteins, identifying in vivo protein partners and understanding the molecular specificity for target protein interactions. Furthermore, the S100 proteins are the only EF-hand proteins that are known to form both homo- and hetero-dimers, and efforts are underway to determine the stabilities of these complexes and structural rationales for their formation and potential differences in their biological roles. This review highlights both the calcium-dependent and -independent interactions of the S100 proteins, with a focus on the structures of the complexes, differences and similarities in the strengths of the interactions, and preferences for homo- compared with hetero-dimeric S100 protein assembly.     

Breeding performance,mate fidelity,and nest site fidelity in a long‐lived seabird: behaving against the current?

There is evidence that breeding failure is associated with divorce and dispersal in many bird species. However, deviations from the general pattern “success‐stay/failure‐leave” seem to be common, suggesting that factors other than breeding performance may importantly influence mate and habitat selection. Moreover, variability in response to performance suggests coexistence of different evolutionary strategies of mate and site selection within a population. In this study, we assessed how individuals conform to the success‐stay/failure‐leave pattern in kittiwakes (Rissa tridactyla), and aimed to identify categories of individuals presenting different behavioural patterns. We considered individual attributes (experience, prior residence at the nest site, performance in multiple breeding attempts), pair attributes (arrival asynchrony, timing of failure, pair duration), and productivity in habitat patches. Timing of failure was an important factor. Pair reunion probability was close to 0.5 in failed pairs, but it was consistently higher in early failed than in late failed pairs. Prior residence better explained variability in probability of reunion in failed pairs than pair duration. However, the positive influence of prior residence on the probability of reunion was perceptible only in early failed pairs. Divorce probability in successful pairs increased with arrival asynchrony, and was higher in first‐time than in experienced breeders. Local productivity positively influenced site fidelity probability in early failed birds, but not in late failed ones. Using memory models, we found that dispersal decisions integrate information on individual breeding performance in a temporal scale longer than one year. This study contributed to the identification of relevant states to be considered when addressing mate and nest site choice. Natural selection may operate on slight fitness differences that cannot be detected without high levels of stratification according to the appropriate individual and habitat attributes.     

Fitness consequences for copepods feeding on a red tide dinoflagellate: deciphering the effects of nutritional value, toxicity, and feeding behavior

Phytoplankton exhibit a diversity of morphologies, nutritional values, and potential chemical defenses that could affect the feeding and fitness of zooplankton consumers. However, how phytoplankton traits shape plant–herbivore interactions in the marine plankton is not as well understood as for terrestrial or marine macrophytes and their grazers. The occurrence of blooms of marine dinoflagellates such as Karenia brevis suggests that, for uncertain reasons, grazers are unable to capitalize on, or control, this phytoplankton growth—making these systems appealing for testing mechanisms of grazing deterrence. Using the sympatric copepod Acartia tonsa, we conducted a mixed diet feeding experiment to test whether K. brevis is beneficial, toxic, nutritionally inadequate, or behaviorally rejected as food relative to the palatable and nutritionally adequate phytoplankter Rhodomonas lens. On diets rich in K. brevis, copepods experienced decreased survivorship and decreased egg production per female, but the percentage of eggs that hatched was unaffected. Although copepods showed a 6–17% preference for R. lens over K. brevis on some mixed diets, overall high ingestion rates eliminated the possibility that reduced copepod fitness was caused by copepods avoiding K. brevis, leaving nutritional inadequacy and toxicity as remaining hypotheses. Because egg production was dependent on the amount of R. lens consumed regardless of the amount of K. brevis eaten, there was no evidence that fitness costs were caused by K. brevis toxicity. Copepods limited to K. brevis ate 480% as much as those fed only R. lens, suggesting that copepods attempted to compensate for low food quality with increased quantity ingested. Our results indicate that K. brevis is a poor food for A. tonsa, probably due to nutritional inadequacy rather than toxicity, which could affect bloom dynamics in the Gulf of Mexico where these species co-occur.     

Responsive regions for direct organogenesis in sunflower cotyledons

Regeneration efficiency from three different regions of cotyledonary explants was examined in six sunflower inbred lines. Proximal, middle and distal regions from seedling cotyledons were cultured on regeneration medium supplemented with growth regulators. Plant regeneration by direct organogenesis was observed after four weeks. Significant differences among inbred lines were found for regeneration percentage and average number of shoots per total explants. Also a decreasing regeneration capacity was observed from proximal to distal sections for all inbred lines. Regeneration ability from cotyledonary explants in this species is strongly influenced by the genotype and by the region from which the explant was obtained. The distance to the cotyledonary node plays a preponderant role in the expression of shoot forming capacity. Shoot differentiation via seedling cotyledons depends upon the presence of the proximal region of cotyledon regardless of the genotype.     

Insights into S100 target specificity examined by a new interaction between S100A11 and annexin A2

S100 proteins are a group of EF-hand calcium-signaling proteins, many of which interact with members of the calcium- and phospholipid-binding annexin family of proteins. This calcium-sensitive interaction enables two neighboring membrane surfaces, complexed to different annexin proteins, to be brought into close proximity for membrane reorganization, using the S100 protein as a bridging molecule. S100A11 and S100A10 are two members of the S100 family found to interact with the N-termini of annexins A1 and A2, respectively. Despite the high degree of structural similarity between these two complexes and the sequences of the peptides, earlier studies have shown that there is little or no cross-reactivity between these two S100s and the annexin peptides. In the current work the specificity and the affinity of the interaction of the N-terminal sequences of annexins A1 and A2 with Ca2+-S100A11 were investigated. Through the use of alanine-scanning peptide array experiments and NMR spectroscopy, an approximate 5-fold tighter interaction was identified between Ca2+-S100A11 and annexin A2 (approximately 3 microM) compared to annexin A1 (approximately 15 microM). Chemical shift mapping revealed that the binding site for annexin A2 on S100A11 was similar to that observed for the annexin A1 but with distinct differences involving the C-terminus of the annexin A2 peptide. In addition, kinetic measurements based on NMR titration data showed that annexin A2 binding to Ca2+-S100A11 occurs at a comparable rate (approximately 120 s(-1)) to that observed for membrane fusion processes such as endo- and exocytosis.     

Genome sequencing and mapping reveal loss of heterozygosity as a mechanism for rapid adaptation in the vegetable pathogen Phytophthora capsici

The oomycete vegetable pathogen Phytophthora capsici has shown remarkable adaptation to fungicides and new hosts. Like other members of this destructive genus, P. capsici has an explosive epidemiology, rapidly producing massive numbers of asexual spores on infected hosts. In addition, P. capsici can remain dormant for years as sexually recombined oospores, making it difficult to produce crops at infested sites, and allowing outcrossing populations to maintain significant genetic variation. Genome sequencing, development of a high-density genetic map, and integrative genomic or genetic characterization of P. capsici field isolates and intercross progeny revealed significant mitotic loss of heterozygosity (LOH) in diverse isolates. LOH was detected in clonally propagated field isolates and sexual progeny, cumulatively affecting >30% of the genome. LOH altered genotypes for more than 11,000 single-nucleotide variant sites and showed a strong association with changes in mating type and pathogenicity. Overall, it appears that LOH may provide a rapid mechanism for fixing alleles and may be an important component of adaptability for P. capsici.