Species-typical songs in white-crowned sparrows tutored with only phrase pairs

Modern theories of learned vocal behaviours, such as human speech and singing in songbirds, posit that acoustic communication signals are reproduced from memory, using auditory feedback. The nature of these memories, however, is unclear. Here we propose and test a model for how complex song structure can emerge from sparse sequence information acquired during tutoring. In this conceptual model, a population of combination-sensitive (phrase-pair) detectors is shaped by early exposure to song and serves as the minimal representation of the template necessary for generating complete song. As predicted by the model, birds that were tutored with only pairs of normally adjacent song phrases were able to assemble full songs in which phrases were placed in the correct order; birds that were tutored with reverse-ordered phrase pairs sang songs with reversed phrase order. Birds that were tutored with all song phrases, but presented singly, failed to produce normal, full songs. These findings provide the first evidence for a minimal requirement of sequence information in the acoustic model that can give rise to correct song structure.     

Sensitivity gains in chemosensing by lasing action in organic polymers

Societal needs for greater security require dramatic improvements in the sensitivity of chemical and biological sensors. To meet this challenge, increasing emphasis in analytical science has been directed towards materials and devices having highly nonlinear characteristics; semiconducting organic polymers (SOPs), with their facile excited state (exciton) transport, are prime examples of amplifying materials. SOPs have also been recognized as promising lasing materials, although the susceptibility of these materials to optical damage has thus far limited applications. Here we report that attenuated lasing in optically pumped SOP thin films displays a sensitivity to vapours of explosives more than 30 times higher than is observed from spontaneous emission. Critical to this achievement was the development of a transducing polymer with high thin-film quantum yield, a high optical damage threshold in ambient atmosphere and a record low lasing threshold. Trace vapours of the explosives 2,4,6-trinitrotoluene (TNT) and 2,4-dinitrotoluene (DNT) introduce non-radiative deactivation pathways that compete with stimulated emission. We demonstrate that the induced cessation of the lasing action, and associated sensitivity enhancement, is most pronounced when films are pumped at intensities near their lasing threshold. The combined gains from amplifying materials and lasing promise to deliver sensors that can detect explosives with unparalleled sensitivity.     

Transcriptional regulation of a metastasis suppressor gene by Tip60 and beta-catenin complexes

Defining the molecular strategies that integrate diverse signalling pathways in the expression of specific gene programmes that are critical in homeostasis and disease remains a central issue in biology. This is particularly pertinent in cancer biology because downregulation of tumour metastasis suppressor genes is a common occurrence, and the underlying molecular mechanisms are not well established. Here we report that the downregulation of a metastasis suppressor gene, KAI1, in prostate cancer cells involves the inhibitory actions of beta-catenin, along with a reptin chromatin remodelling complex. This inhibitory function of beta-catenin-reptin requires both increased beta-catenin expression and recruitment of histone deacetylase activity. The coordinated actions of beta-catenin-reptin components that mediate the repressive state serve to antagonize a Tip60 coactivator complex that is required for activation; the balance of these opposing complexes controls the expression of KAI1 and metastatic potential. The molecular mechanisms underlying the antagonistic regulation of beta-catenin-reptin and the Tip60 coactivator complexes for the metastasis suppressor gene, KAI1, are likely to be prototypic of a selective downregulation strategy for many genes, including a subset of NF-kappaB target genes.     

Dissociative hydrogen adsorption on palladium requires aggregates of three or more vacancies

During reaction, a catalyst surface usually interacts with a constantly fluctuating mix of reactants, products, 'spectators' that do not participate in the reaction, and species that either promote or inhibit the activity of the catalyst. How molecules adsorb and dissociate under such dynamic conditions is often poorly understood. For example, the dissociative adsorption of the diatomic molecule H2--a central step in many industrially important catalytic processes--is generally assumed to require at least two adjacent and empty atomic adsorption sites (or vacancies). The creation of active sites for H2 dissociation will thus involve the formation of individual vacancies and their subsequent diffusion and aggregation, with the coupling between these events determining the activity of the catalyst surface. But even though active sites are the central component of most reaction models, the processes controlling their formation, and hence the activity of a catalyst surface, have never been captured experimentally. Here we report scanning tunnelling microscopy observations of the transient formation of active sites for the dissociative adsorption of H2 molecules on a palladium (111) surface. We find, contrary to conventional thinking, that two-vacancy sites seem inactive, and that aggregates of three or more hydrogen vacancies are required for efficient H2 dissociation.     

Truncated TrkB-T1 mediates neurotrophin-evoked calcium signalling in glia cells

The neurotrophin receptor TrkB is essential for normal function of the mammalian brain. It is expressed in three splice variants. Full-length receptors (TrkB(FL)) possess an intracellular tyrosine kinase domain and are considered as those TrkB receptors that mediate the crucial effects of brain-derived neurotrophic factor (BDNF) or neurotrophin 4/5 (NT-4/5). By contrast, truncated receptors (TrkB-T1 and TrkB-T2) lack tyrosine kinase activity and have not been reported to elicit rapid intracellular signalling. Here we show that astrocytes predominately express TrkB-T1 and respond to brief application of BDNF by releasing calcium from intracellular stores. The calcium transients are insensitive to the tyrosine kinase blocker K-252a and persist in mutant mice lacking TrkB(FL). By contrast, neurons produce rapid BDNF-evoked signals through TrkB(FL) and the Na(v)1.9 channel. Expression of antisense TrkB messenger RNA strongly reduces BDNF-evoked calcium signals in glia. Thus, our results show that, unexpectedly, TrkB-T1 has a direct signalling role in mediating inositol-1,4,5-trisphosphate-dependent calcium release; in addition, they identify a previously unknown mechanism of neurotrophin action in the brain.     

Isolation of the closed circular form of the transposable element Tc1 in Caenorhabditis elegans

The mobilization of Tc1, a transposable element in the genome of the roundworm Caenorhabditis elegans, has been investigated. Genomic blot hybridization has shown that Tc1 exists in very different numbers in the genomes of two closely related strains of C. elegans: there are approximately 30 copies of Tc1 in the Bristol strain, whereas in the Bergerac strain there are 200-300. Most of these Tc1 elements are structurally highly conserved although there exists a second form which contains a HindIII restriction site (Tc1 (Hin) form) and comprises approximately 10% of the population. Excision of Tc1 from its chromosomal location in the Bergerac strain is indicated by the presence, on genomic blots, of a minor band corresponding to the size of the uninserted restriction fragment. Here we describe the recovery of extrachromosomal linear and closed circular copies of Tc1 from the Bergerac strain, presumably a result of Tc1 excision.     

Lymphopenia and lymphocyte transformation in alcoholics

Summary The basis of peripheral blood lymphopenia observed in patients with chronic alcoholism and liver disease was investigated by examining the effect of sera of these patients on in vitro transformation of normal human peripheral blood lymphocytes. A positive correlation was demonstrated between the serum inhibition of phytohaemagglutinin- and pokeweed mitogen-induced transformation and the degree of lymphopenia. Thus serum factors may contribute to the observed lymphopenia by inhibiting lymphocyte production in vivo.This study was supported by grants from the National Health and Medical Research Council of Australia, Royal Australasian College of Physicians and Alfred Hospital Henry Laurie Scholarship Fund.