The signaller's dilemma: a cost-benefit analysis of public and private communication

Background

Understanding the diversity of animal signals requires knowledge of factors which may influence the different stages of communication, from the production of a signal by the sender up to the detection, identification and final decision-making in the receiver. Yet, many studies on signalling systems focus exclusively on the sender, and often ignore the receiver side and the ecological conditions under which signals evolve.

Methodology/Principal Findings

We study a neotropical katydid which uses airborne sound for long distance communication, but also an alternative form of private signalling through substrate vibration. We quantified the strength of predation by bats which eavesdrop on the airborne sound signal, by analysing insect remains at roosts of a bat family. Males do not arbitrarily use one or the other channel for communication, but spend more time with private signalling under full moon conditions, when the nocturnal rainforest favours predation by visually hunting predators. Measurements of metabolic CO₂-production rate indicate that the energy necessary for signalling increases 3-fold in full moon nights when private signalling is favoured. The background noise level for the airborne sound channel can amount to 70 dB SPL, whereas it is low in the vibration channel in the low frequency range of the vibration signal. The active space of the airborne sound signal varies between 22 and 35 meters, contrasting with about 4 meters with the vibration signal transmitted on the insect''s favourite roost plant. Signal perception was studied using neurophysiological methods under outdoor conditions, which is more reliable for the private mode of communication.

Conclusions/Significance

Our results demonstrate the complex effects of ecological conditions, such as predation, nocturnal ambient light levels, and masking noise levels on the performance of receivers in detecting mating signals, and that the net advantage or disadvantage of a mode of communication strongly depends on these conditions.     

Generation of Human Antigen-Specific Monoclonal IgM Antibodies Using Vaccinated “Human Immune System” Mice

Background

Passive transfer of antibodies not only provides immediate short-term protection against disease, but also can be exploited as a therapeutic tool. However, the ‘humanization’ of murine monoclonal antibodies (mAbs) is a time-consuming and expensive process that has the inherent drawback of potentially altering antigenic specificity and/or affinity. The immortalization of human B cells represents an alternative for obtaining human mAbs, but relies on the availability of biological samples from vaccinated individuals or convalescent patients. In this work we describe a novel approach to generate fully human mAbs by combining a humanized mouse model with a new B cell immortalization technique.

Methodology/Principal Findings

After transplantation with CD34⁺CD38⁻ human hematopoietic progenitor cells, BALB/c Rag2^−/−IL-2Rγc^−/− mice acquire a human immune system and harbor B cells with a diverse IgM repertoire. “Human Immune System” mice were then immunized with two commercial vaccine antigens, tetanus toxoid and hepatitis B surface antigen. Sorted human CD19⁺CD27⁺ B cells were retrovirally transduced with the human B cell lymphoma (BCL)-6 and BCL-XL genes, and subsequently cultured in the presence of CD40-ligand and IL-21. This procedure allows generating stable B cell receptor-positive B cells that secrete immunoglobulins. We recovered stable B cell clones that produced IgM specific for tetanus toxoid and the hepatitis B surface antigen, respectively.

Conclusion/Significance

This work provides the proof-of-concept for the usefulness of this novel method based on the immunization of humanized mice for the rapid generation of human mAbs against a wide range of antigens.     

The strength of the HIV-1 3' splice sites affects Rev function

Background

Of the diverse subtypes of Human Immunodeficiency Virus Type-1 (HIV-1), subtype-C strains cause a large majority of infections worldwide. The reasons for the global dominance of HIV-1 subtype-C infections are not completely understood. Tat, being critical for viral infectivity and pathogenesis, may differentially modulate pathogenic properties of the viral subtypes. Biochemical studies on Tat are hampered by the limitations of the current purification protocols. Tat purified using standard protocols often is competent for transactivation activity but defective for a variety of other biological functions. Keeping this limitation in view, we developed an efficient protein purification strategy for Tat.

Results

Tat proteins obtained using the novel strategy described here were free of contaminants and retained biological functions as evaluated in a range of assays including the induction of cytokines, upregulation of chemokine coreceptor, transactivation of the viral promoter and rescue of a Tat-defective virus. Given the highly unstable nature of Tat, we evaluated the effect of the storage conditions on the biological function of Tat following purification. Tat stored in a lyophilized form retained complete biological activity regardless of the storage temperature. To understand if variations in the primary structure of Tat could influence the secondary structure of the protein and consequently its biological functions, we determined the CD spectra of subtype-C and -B Tat proteins. We demonstrate that subtype-C Tat may have a relatively higher ordered structure and be less flexible than subtype-B Tat. We show that subtype-C Tat as a protein, but not as a DNA expression vector, was consistently inferior to subtype-B Tat in a variety of biological assays. Furthermore, using ELISA, we evaluated the anti-Tat antibody titers in a large number of primary clinical samples (n = 200) collected from all four southern Indian states. Our analysis of the Indian populations demonstrated that Tat is non-immunodominant and that a large variation exists in the antigen-specific antibody titers.

Conclusion

Our report not only describes a simple protein purification strategy for Tat but also demonstrates important structural and functional differences between subtype-B and -C Tat proteins. Furthermore, this is the first report of protein purification and characterization of subtype-C Tat.     

Simultaneous apocrine and merocrine secretion in the rat coagulating gland

The coagulating gland of the rat synthesizes two prevalent secretory proteins (transglutaminase and 115 K) that are discharched in a different manner, one being secreted in an apocrine fashion (transglutaminase) and the other one in a merocrine way (115 K). Differences in the intra- cellular pathway and the release of either protein were studied using immunofluorescence on semithin sections, immunoelectron microscopy of preembedding-processed chopper sections and postembedding-processed ultrathin sections of rat coagulating gland. Immunohistochemical staining using an anti-transglutaminase antibody resulted in dense labeling of the cytoplasm of secretory cells and their apical blebs, whereas the cisternae of the rough endoplasmic reticulum and the Golgi apparatus were completely unlabeled. When, on the contrary, the anti-115 K antiserum was used, dense labeling of the cisternae of the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules was seen. Intraluminal secretion was also labeled, but the secretory blebs remained unlabeled. Our findings show that, in the coagulating gland of the male rat, the two secretory proteins studied are processed in parallel, but at completely different intracellular pathways. They are released via different extrusion mechanisms. Transglutaminase is synthesized outside the endoplasmic reticulum, reaches the apical cell pole by free flow in the cytoplasm, and is released via apocrine blebs, the membranes of which appear to be derived from the apical plasma membrane. The protein 115 K, on the other hand, follows the classic route, being synthesized within the cisternae of rough endoplasmic reticulum, subsequently glycosylated in the Golgi apparatus, and released in a merocrine fashion. The mutual exclusion of the two secretory pathways and the regulation of the alternative release mechanism are still unresolved issues.     

Computer-assisted phenotype characterization for genetic research in psychiatry

Psychiatric disorders differ from other complex phenotypes in their lack of objectively assessable biological markers that contribute to the establishment of a research diagnosis for genetic studies. To nevertheless allow for the delineation of genetically meaningful diagnostic entities for psychiatric genetic research, comprehensive phenotype characterization procedures are required. It is widely agreed that these should include the standardized assessment of life-time clinical symptomatology, sociodemographic, and environmental factors. Data should be based on several sources, i.e. diagnostic interviews with probands and their relatives as well as a thorough review of medical records, and final assignment of diagnosis should follow robust algorithms (i.e. best-estimate procedures, consensus diagnosis). Here, we outline a practical implementation of such a phenotype characterization strategy, including patient recruitment, study enrolment procedures, comprehensive diagnostic assessment, and data management. We argue that successful psychiatric phenotype characterization requires flexible tools. For this purpose, we have developed a computer-assisted phenotype characterization inventory, built around the backbone of a relational database. It allows for the straightforward assessment of symptoms, automated error checks and diagnostic assignment, easily manageable data storage and handling, and flexible data transfer between various research centers even across language barriers, while at the same time keeping up with the highest standards for the protection of sensitive patient data.     

Role and regulation of TRP channels in neutrophil granulocytes

Members of the transient receptor potential (TRP) family for which mRNA can be demonstrated in neutrophil granulocytes with RT-PCR include TRPC6 (as only "short" TRP), TRPM2, TRPV1, TRPV2, TRPV5 and TRPV6. When these are analyzed in heterologous overexpression experiments, TRPM2 is the only cation channel with characteristic properties that can be used as fingerprint to provide functional evidence for its expression in neutrophil granulocytes. As cells transfected with TRPM2, neutrophil granulocytes display non-selective cation currents and typical channel activity evoked by intracellular ADP-ribose and NAD. Thus, stimulation of TRPM2 is likely to occur after activation of CD38 (producing ADP-ribose) and during the oxidative burst (enhancing the NAD concentration). This novel mode of cation entry regulation may be of particular importance for the response of granulocytes to chemoattractants. TRPV6 is a likely but not exclusive candidate as subunit of the channels mediating store-operated Ca2+ entry (SOCE). Evidence for SOCE in granulocytes has been presented with the fura-2 technique but not with electrophysiological methods although Ca2+-selective store-operated currents can be demonstrated in HL-60 cells, a cell culture model of neutrophil granulocytes.     

Mechanism-based inactivation of thioredoxin reductase from Plasmodium falciparum by Mannich bases. Implication for cytotoxicity

Thioredoxin reductase (TrxR) is the homodimeric flavoenzyme that catalyzes reduction of thioredoxin disulfide (Trx). For Plasmodium falciparum, a causative agent of tropical malaria, TrxR is an essential protein which has been validated as a drug target. The high-throughput screening of 350000 compounds has identified Mannich bases as a new class of TrxR mechanism-based inhibitors. During catalysis, TrxR conducts reducing equivalents from the NADPH-reduced flavin to Trx via the two redox-active cysteine pairs, Cys88-Cys93 and Cys535'-Cys540', referred to as N-terminal and C-terminal cysteine pairs. The structures of unsaturated Mannich bases suggested that they could act as bisalkylating agents leading to a macrocycle that involves both C-terminal cysteines of TrxR. To confirm this hypothesis, different Mannich bases possessing one or two electrophilic centers were synthesized and first studied in detail using glutathione as a model thiol. Michael addition of glutathione to the double bond of an unsaturated Mannich base (3a) occurs readily at physiological pH. Elimination of the amino group, promoted by base-catalyzed enolization of the ketone, is followed by addition of a second nucleophile. The intermediate formed in this reaction is an alpha,beta-unsaturated ketone that can react rapidly with a second thiol. When studying TrxR as a target of Mannich bases, we took advantage of the fact that the charge-transfer complex formed between the thiolate of Cys88 and the flavin in the reduced enzyme can be observed spectroscopically. The data show that it is the C-terminal Cys 535'-Cys540' pair rather than the N-terminal Cys88-Cys93 pair that is modified by the inhibitor. Although alkylated TrxR is unable to turn over its natural substrate Trx, it can reduce low M(r) electron acceptors such as methyl methanethiolsulfonate by using its unmodified N-terminal thiols. On the basis of results with chemically distinct Mannich bases, a detailed mechanism for the inactivation of TrxR is proposed.