Is attenuation of tRNA charging responsible for the inhibition of protein labelling accompanying depolarisation of the cerebral cortical cells?

Summary Topical application of concentrated solutions of KCl resulted in reduction of charging of tRNA 7 min after s.c. injection of L-(U-¹⁴C) leucine. Neither radioactivity nor pool size of the total amino acids changed during this period.     

Influence of age on the renal renin response to a high salt intake in the rat

Summary Saline drinking combined with DOCA-treatment was found to decrease renal renin in weanlings at a higher rate than in adult rats, with a comparable saline consumption level. The decrease was not potentiated by uninephrectomy.     

The structure of jhanilactone

Summary The molecular structure and absolute configurationI was assigned to jhanilactone, a new lactone fromEupatorium jhanii Robinson, on the basis of X-ray crystallography and circular dichroism data.Part 37 in the series Chemistry of the Composites. For Part 36, see A.G. González, J. Bermejo, I. Cabrera, G.M. Massanet, H. Mansilla and J.M. Amaro, Phytochemistry, submitted for publication.Acknowledgment. We thank Prof. S. García-Blanco, Instituto Rocasolano, Madrid for the use of an X-ray diffractometer and Prof D.N. Kirk, Westfield College, London for the CD data.     

Entrained rhythmic activities of neuronal ensembles as perceptual memory of time interval

The ability to process temporal information is fundamental to sensory perception, cognitive processing and motor behaviour of all living organisms, from amoebae to humans. Neural circuit mechanisms based on neuronal and synaptic properties have been shown to process temporal information over the range of tens of microseconds to hundreds of milliseconds. How neural circuits process temporal information in the range of seconds to minutes is much less understood. Studies of working memory in monkeys and rats have shown that neurons in the prefrontal cortex, the parietal cortex and the thalamus exhibit ramping activities that linearly correlate with the lapse of time until the end of a specific time interval of several seconds that the animal is trained to memorize. Many organisms can also memorize the time interval of rhythmic sensory stimuli in the timescale of seconds and can coordinate motor behaviour accordingly, for example, by keeping the rhythm after exposure to the beat of music. Here we report a form of rhythmic activity among specific neuronal ensembles in the zebrafish optic tectum, which retains the memory of the time interval (in the order of seconds) of repetitive sensory stimuli for a duration of up to approximately 20 s. After repetitive visual conditioning stimulation (CS) of zebrafish larvae, we observed rhythmic post-CS activities among specific tectal neuronal ensembles, with a regular interval that closely matched the CS. Visuomotor behaviour of the zebrafish larvae also showed regular post-CS repetitions at the entrained time interval that correlated with rhythmic neuronal ensemble activities in the tectum. Thus, rhythmic activities among specific neuronal ensembles may act as an adjustable 'metronome' for time intervals in the order of seconds, and serve as a mechanism for the short-term perceptual memory of rhythmic sensory experience.     

Depth of a strong jovian jet from a planetary-scale disturbance driven by storms

The atmospheres of the gas giant planets (Jupiter and Saturn) contain jets that dominate the circulation at visible levels. The power source for these jets (solar radiation, internal heat, or both) and their vertical structure below the upper cloud are major open questions in the atmospheric circulation and meteorology of giant planets. Several observations and in situ measurements found intense winds at a depth of 24 bar, and have been interpreted as supporting an internal heat source. This issue remains controversial, in part because of effects from the local meteorology. Here we report observations and modelling of two plumes in Jupiter's atmosphere that erupted at the same latitude as the strongest jet (23 degrees N). The plumes reached a height of 30 km above the surrounding clouds, moved faster than any other feature (169 m s(-1)), and left in their wake a turbulent planetary-scale disturbance containing red aerosols. On the basis of dynamical modelling, we conclude that the data are consistent only with a wind that extends well below the level where solar radiation is deposited.     

DNA transposons in vertebrate functional genomics

Genome sequences of many model organisms of developmental or agricultural importance are becoming available. The tremendous amount of sequence data is fuelling the next phases of challenging research: annotating all genes with functional information, and devising new ways for the experimental manipulation of vertebrate genomes. Transposable elements are known to be efficient carriers of foreign DNA into cells. Notably, members of the Tc1/mariner and the hAT transposon families retain their high transpositional activities in species other than their hosts. Indeed, several of these elements have been successfully used for transgenesis and insertional mutagenesis, expanding our abilities in genome manipulations in vertebrate model organisms. Transposon-based genetic tools can help scientists to understand mechanisms of embryonic development and pathogenesis, and will likely contribute to successful human gene therapy. We discuss the possibilities of transposon-based techniques in functional genomics, and review the latest results achieved by the most active DNA transposons in vertebrates. We put emphasis on the evolution and regulation of members of the best-characterized and most widely used Tc1/mariner family.Received 8 June 2004; received after revision 26 October 2004; accepted 18 November 2004     

Endocytosis mechanism of P2Y2 nucleotide receptor tagged with green fluorescent protein: clathrin and actin cytoskeleton dependence

Extracellular nucleotides exert a large number of physiological effects through activation of P2Y receptors. We expressed rat P2Y₂ (rP2Y₂) receptor, tagged with green fluorescent protein (GFP) in HEK-293 cells and visualized receptor translocation in live cells by confocal microscopy. Functional receptor expression was confirmed by determining [Ca²⁺]_i responses. Agonist stimulation caused a time-dependent translocation of the receptor from the plasma membrane to the cytoplasm. Rearrangement of the actin cytoskeleton was observed during agonist-mediated rP2Y₂-GFP receptor internalization. Colocalization of the internalized receptor with early endosomes, clathrin and lysosomes was detected by confocal microscopy. The inhibition of receptor endocytosis by either high-density medium or chlorpromazine in the presence of UTP indicates that the receptor was internalized by the clathrin-mediated pathway. The caveolin- mediated pathway was not involved. Targeting of the receptor from endosomes to lysosomes seems to involve the proteasome pathway, because proteasomal inhibition increased receptor recycling back to the plasma membrane.Received 8 February 2005; received after revision 18 March 2005; accepted 11 April 2005     

Lipoprotein particles are required for Hedgehog and Wingless signalling

Wnt and Hedgehog family proteins are secreted signalling molecules (morphogens) that act at both long and short range to control growth and patterning during development. Both proteins are covalently modified by lipid, and the mechanism by which such hydrophobic molecules might spread over long distances is unknown. Here we show that Wingless, Hedgehog and glycophosphatidylinositol-linked proteins copurify with lipoprotein particles, and co-localize with them in the developing wing epithelium of Drosophila. In larvae with reduced lipoprotein levels, Hedgehog accumulates near its site of production, and fails to signal over its normal range. Similarly, the range of Wingless signalling is narrowed. We propose a novel function for lipoprotein particles, in which they act as vehicles for the movement of lipid-linked morphogens and glycophosphatidylinositol-linked proteins.