A novel octopamine receptor with preferential expression in <i>Drosophila</i> mushroom bodies

Octopamine is a neuromodulator that mediates diverse physiological processes in invertebrates. In some insects, such as honeybees and fruit flies, octopamine has been shown to be a major stimulator of adenylyl cyclase and to function in associative learning. To identify an octopamine receptor mediating this function in Drosophila, putative biogenic amine receptors were cloned by a novel procedure using PCR and single-strand conformation polymorphism. One new receptor, octopamine receptor in mushroom bodies (OAMB), was identified as an octopamine receptor because human and Drosophila cell lines expressing OAMB showed increased cAMP and intracellular Ca2+ levels after octopamine application. Immunohistochemical analysis using an antibody made to the receptor revealed highly enriched expression in the mushroom body neuropil and the ellipsoid body of central complex, brain areas known to be crucial for olfactory learning and motor control, respectively. The preferential expression of OAMB in mushroom bodies and its capacity to produce cAMP accumulation suggest an important role in synaptic modulation underlying behavioral plasticity

Latrunculin A delays anaphase onset in fission yeast by disrupting an ase1-independent pathway controlling mitotic spindle stability

It has been proposed previously that latrunculin A, an inhibitor of actin polymerization, delays the onset of anaphase by causing spindle misorientation in fission yeast. However, we show that {Delta}mto1 cells, which are defective in nucleation of cytoplasmic microtubules, have profoundly misoriented spindles but are not delayed in the timing of sister chromatid separation, providing compelling evidence that fission yeast does not possess a spindle orientation checkpoint. Instead, we show that latrunculin A delays anaphase onset by disrupting interpolar microtubule stability. This effect is abolished in a latrunculin A-insensitive actin mutant and exacerbated in cells lacking Ase1, which cross-links antiparallel interpolar microtubules at the spindle midzone both before and after anaphase. These data indicate that both Ase1 and an intact actin cytoskeleton are required for preanaphase spindle stability. Finally, we show that loss of Ase1 activates a checkpoint that requires only the Mad3, Bub1, and Mph1, but not Mad1, Mad2, or Bub3 checkpoint proteins

Checkpoint proteins come under scrutiny

Details are emerging of the interactions between the kinetochore and various spindle checkpoint proteins that ensure that sister chromatids are equally divided between daughter cells during cell division

Spin orbit coupling in itinerant-electron magnetism

Imperial Users onl

Watching the hands of the Arabidopsis biological clock

Oligonucleotide and cDNA microarrays have been used to analyse the mRNA levels of 8,000 genes in Arabidopsis thaliana throughout the day/night cycle. Genes involved in signal transduction and in various metabolic pathways were found to be coordinately regulated by circadian rhythms and/or by light

Torsion and bending of nucleic acids studied by subnanosecond time-resolved fluorescence depolarization of intercalated dyes

Subnanosecond time‐resolved fluorescence depolarization has been used to monitor the reorientation of ethidium bromide intercalated in native DNA, synthetic polynucleotide complexes, and in supercoiled plasmid DNA. The fluorescence polarization anisotropy was successfully analyzed with an elastic model of DNA dynamics, including both torsion and bending, which yielded an accurate value for the torsional rigidity of the different DNA samples. The dependence of the torsional rigidity on the base sequence, helical structure, and tertiary structure was experimentally observed. The magnitude of the polyelectrolyte contribution to the torsional rigidity of DNA was measured over a wide range of ionic strength, and compared with polyelectrolyte theories for the persistence length. We also observed a rapid initial reorientation of the intercalated ethidium which had a much smaller amplitude in RNA than in DNA

A New Operation on Sequences: the Boustrouphedon Transform

A generalization of the Seidel-Entringer-Arnold method for calculating the alternating permutation numbers (or secant-tangent numbers) leads to a new operation on integer sequences, the Boustrophedon transform.Comment: very minor change: corrected typo in author list. June 24 2002: correction to a proof; additional reference

Robustness from flexibility in the fungal circadian clock

Background Robustness is a central property of living systems, enabling function to be maintained against environmental perturbations. A key challenge is to identify the structures in biological circuits that confer system-level properties such as robustness. Circadian clocks allow organisms to adapt to the predictable changes of the 24-hour day/night cycle by generating endogenous rhythms that can be entrained to the external cycle. In all organisms, the clock circuits typically comprise multiple interlocked feedback loops controlling the rhythmic expression of key genes. Previously, we showed that such architectures increase the flexibility of the clock's rhythmic behaviour. We now test the relationship between flexibility and robustness, using a mathematical model of the circuit controlling conidiation in the fungus Neurospora crassa. Results The circuit modelled in this work consists of a central negative feedback loop, in which the frequency (frq) gene inhibits its transcriptional activator white collar-1 (wc-1), interlocked with a positive feedback loop in which FRQ protein upregulates WC-1 production. Importantly, our model reproduces the observed entrainment of this circuit under light/dark cycles with varying photoperiod and cycle duration. Our simulations show that whilst the level of frq mRNA is driven directly by the light input, the falling phase of FRQ protein, a molecular correlate of conidiation, maintains a constant phase that is uncoupled from the times of dawn and dusk. The model predicts the behaviour of mutants that uncouple WC-1 production from FRQ's positive feedback, and shows that the positive loop enhances the buffering of conidiation phase against seasonal photoperiod changes. This property is quantified using Kitano's measure for the overall robustness of a regulated system output. Further analysis demonstrates that this functional robustness is a consequence of the greater evolutionary flexibility conferred on the circuit by the interlocking loop structure. Conclusions Our model shows that the behaviour of the fungal clock in light-dark cycles can be accounted for by a transcription-translation feedback model of the central FRQ-WC oscillator. More generally, we provide an example of a biological circuit in which greater flexibility yields improved robustness, while also introducing novel sensitivity analysis techniques applicable to a broader range of cellular oscillators

Time-resolved spectroscopy of macromolecules: Effect of helical structure on the torsional dynamics of DNA and RNA

The torsional rigidity of DNA and RNA is measured via the fluorescence depolarization technique