Differential activation of myotube nuclei following exposure to an acetylcholine receptor-inducing factor

A glycoprotein purified from chick brain, of relative molecular mass 42,000, increases the rate of appearance of acetylcholine receptors (AChRs) on the surface of chick myotubes. RNase protection assays have shown that this AChR-inducing activity (ARIA) increases the amount of mRNA encoding the alpha-subunit of the AChR, with little or no effect on the amounts of gamma- and delta-mRNAs2. Here, we report that the mRNAs encoding the alpha- and gamma-subunits of the receptor detected by in situ hybridization are concentrated around nuclei in cultured myotubes. Consistent with previous results, ARIA selectively increased the amount of alpha-subunit mRNA, but we now find that all nuclei were not activated to the same extent, with a substantial number not responding at all. Assuming that ARIA is released by motor nerve terminals, our results indicate that only a subset of muscle nuclei are capable of contributing to the accumulation of AChRs at developing neuromuscular junctions.     

Spike train dynamics predicts theta-related phase precession in hippocampal pyramidal cells

According to the temporal coding hypothesis, neurons encode information by the exact timing of spikes. An example of temporal coding is the hippocampal phase precession phenomenon, in which the timing of pyramidal cell spikes relative to the theta rhythm shows a unidirectional forward precession during spatial behaviour. Here we show that phase precession occurs in both spatial and non-spatial behaviours. We found that spike phase correlated with instantaneous discharge rate, and processed unidirectionally at high rates, regardless of behaviour. The spatial phase precession phenomenon is therefore a manifestation of a more fundamental principle governing the timing of pyramidal cell discharge. We suggest that intrinsic properties of pyramidal cells have a key role in determining spike times, and that the interplay between the magnitude of dendritic excitation and rhythmic inhibition of the somatic region is responsible for the phase assignment of spikes.     

The c-myc oncogene driven by immunoglobulin enhancers induces lymphoid malignancy in transgenic mice

Transgenic mice bearing the cellular myc oncogene coupled to the immunoglobulin mu or kappa enhancer frequently develop a fatal lymphoma within a few months of birth. Since the tumours represent represent both immature and mature B lymphocytes, constitutive c-myc expression appears to be highly leukaemogenic at several stages of B-cell maturation. These myc mice should aid study of lymphoma development, B-cell ontogeny and immunoglobulin regulation.     

Complete genome sequence of the model actinomycete Streptomyces coelicolor A3(2)

Streptomyces coelicolor is a representative of the group of soil-dwelling, filamentous bacteria responsible for producing most natural antibiotics used in human and veterinary medicine. Here we report the 8,667,507 base pair linear chromosome of this organism, containing the largest number of genes so far discovered in a bacterium. The 7,825 predicted genes include more than 20 clusters coding for known or predicted secondary metabolites. The genome contains an unprecedented proportion of regulatory genes, predominantly those likely to be involved in responses to external stimuli and stresses, and many duplicated gene sets that may represent 'tissue-specific' isoforms operating in different phases of colonial development, a unique situation for a bacterium. An ancient synteny was revealed between the central 'core' of the chromosome and the whole chromosome of pathogens Mycobacterium tuberculosis and Corynebacterium diphtheriae. The genome sequence will greatly increase our understanding of microbial life in the soil as well as aiding the generation of new drug candidates by genetic engineering.