Odour concentration affects odour identity in honeybees

The fact that most types of sensory stimuli occur naturally over a large range of intensities is a challenge to early sensory processing. Sensory mechanisms appear to be optimized to extract perceptually significant stimulus fluctuations that can be analysed in a manner largely independent of the absolute stimulus intensity. This general principle may not, however, extend to olfaction; many studies have suggested that olfactory stimuli are not perceptually invariant with respect to odour intensity. For many animals, absolute odour intensity may be a feature in itself, such that it forms a part of odour identity and thus plays an important role in discrimination alongside other odour properties such as the molecular identity of the odorant. The experiments with honeybees reported here show a departure from odour-concentration invariance and are consistent with a lower-concentration regime in which odour concentration contributes to overall odour identity and a higher-concentration regime in which it may not. We argue that this could be a natural consequence of odour coding and suggest how an 'intensity feature' might be useful to the honeybee in natural odour detection and discrimination.     

Docking and rolling, a model of how the mitotic motor Eg5 works

Whereas kinesin I is designed to transport cargoes long distances in isolation, a closely related kinesin motor, Eg5, is designed to generate a sustained opposing force necessary for proper mitotic spindle formation. Do the very different roles for these evolutionarily related motors translate into differences in how they generate movement? We have addressed this question by examining when in the ATPase cycle the Eg5 motor domain and neck linker move through the use of a series of novel spectroscopic probes utilizing fluorescence resonance energy transfer, and we have compared our results to kinesin I. Our results are consistent with a model in which movement in Eg5 occurs in two sequential steps, an ATP-dependent docking of the neck linker, followed by a rotation or "rolling" of the entire motor domain on the microtubule surface that occurs with ATP hydrolysis. These two forms of movement are consistent with the functions of a motor designed to generate sustained opposing force, and hence, our findings support the argument that the mechanochemical features of a molecular motor are shaped more by the demands placed on it than by its particular family of origin.     

Assessment of dominance hierarchy through urine scent marking and its chemical constituents in male blackbuck Antelope cervicapra, a critically endangered species

In ungulates the process of chemical communication by urinary scent marking has been directly related to reproductive dominance, territorial defense and proximity to resources. The differences in the frequency of urine marking and chemical composition of urine of males Antelope cervicapra before, during and after the dominance hierarchy period were assessed. The variations in the urine marking and its chemical profiles of dominant males (n = 9), bachelors (n = 5) and sub-adult males (n = 5) were compared to find out how the dominance hierarchy influences the confined blackbuck herd under semi-natural captive conditions. The frequency of urine marking is significantly higher (p < 0.001) in dominant males. Twenty-eight major constituents were identified in the urine of dominant males (before, during and after the dominance hierarchy period), bachelor and sub-adult males. Among these, three specific compounds namely, 3-hexanone (I), 6-methyl-5-hepten-2-one (II) and 4-methyl-3-heptanone (III) were seen only in dominant males urine during the dominance hierarchy period. Based on the behavioural observation and the unique chemical constituents in the urine, it is concluded that the dominant male scent odor suppresses aggression, scent marking, scent production and territorial patrolling activities of subordinate males, through which the dominant male establish their hierarchy and attains success in reproduction.     

Reversal of a mutator activity by a nearby fidelity-neutral substitution in the RB69 DNA polymerase binding pocket

Phage RB69 B-family DNA polymerase is responsible for the overall high fidelity of RB69 DNA synthesis. Fidelity is compromised when conserved Tyr567, one of the residues that form the nascent polymerase base-pair binding pocket, is replaced by alanine. The Y567A mutator mutant has an enlarged binding pocket and can incorporate and extend mispairs efficiently. Ser565 is a nearby conserved residue that also contributes to the binding pocket, but a S565G replacement has only a small impact on DNA replication fidelity. When Y567A and S565G replacements were combined, mutator activity was strongly decreased compared to that with Y567A replacement alone. Analyses conducted both in vivo and in vitro revealed that, compared to Y567A replacement alone, the double mutant mainly reduced base substitution mutations and, to a lesser extent, frameshift mutations. The decrease in mutation rates was not due to increased exonuclease activity. Based on measurements of DNA binding affinity, mismatch insertion, and mismatch extension, we propose that the recovered fidelity of the double mutant may result, in part, from an increased dissociation of the enzyme from DNA, followed by the binding of the same or another polymerase molecule in either exonuclease mode or polymerase mode. An additional antimutagenic factor may be a structural alteration in the polymerase binding pocket described in this article.     

Strong TCR conservation and altered T cell cross-reactivity characterize a B*57-restricted immune response in HIV-1 infection

HLA-B*57 is associated with slower disease progression to AIDS, and CD8+ T cell responses to B*57-restricted epitopes are thought to contribute to this protective effect. In this study, we evaluate the B*57-restricted p24 KAFSPEVIPMF (KF11) immune response which is immunodominant during chronic infection. Previously, we observed that the KF11 clade variants KGFNPEVIPMF [A2G,S4N] and KAFNPEIIMPF [S4N,V7I], sharing a position 4 mutation, are differentially recognized by KF11-specific T cells. By combining structural and cellular studies, we now demonstrate that the KF11 and [A2G,S4N] epitopes induce distinct functional responses in [A2G,S4N] and KF11-specific T cells, respectively, despite minimal structural differences between the individual B*57-peptide complexes. Recently, we also elucidated the highly distinct structure of KF11 in complex with B*5703, and have now characterized the CD8+ T cell repertoire recognizing this epitope. We now report striking features of TCR conservation both in terms of TCR Valpha and Vbeta chain usage, and throughout the hypervariable region. Collectively, our findings highlight unusual features of the B*5701/B*5703-KF11-specific immune responses which could influence disease progression and that might be important to consider when designing future vaccine regimens.     

Translational repression restricts expression of the C. elegans Nanos homolog NOS-2 to the embryonic germline

Members of the nanos gene family are evolutionarily conserved regulators of germ cell development. In several organisms, Nanos protein expression is restricted to the primordial germ cells (PGCs) during early embryogenesis. Here, we investigate the regulation of the Caenorhabditis elegans nanos homolog nos-2. We find that the nos-2 RNA is translationally repressed. In the adult germline, translation of the nos-2 RNA is inhibited in growing oocytes, and this inhibition depends on a short stem loop in the nos-2 3'UTR. In embryos, nos-2 translation is repressed in early blastomeres, and this inhibition depends on a second region in the nos-2 3'UTR. nos-2 RNA is also degraded in somatic blastomeres by a process that is independent of translational repression and requires the CCCH finger proteins MEX-5 and MEX-6. Finally, the germ plasm component POS-1 activates nos-2 translation in the PGCs. A combination of translational repression, RNA degradation, and activation by germ plasm has also been implicated in the regulation of nanos homologs in Drosophila and zebrafish, suggesting the existence of conserved mechanisms to restrict Nanos expression to the germline.