The two ADF-H domains of twinfilin play functionally distinct roles in interactions with actin monomers

Twinfilin is a ubiquitous and abundant actin monomer-binding protein that is composed of two ADF-H domains. To elucidate the role of twinfilin in actin dynamics, we examined the interactions of mouse twinfilin and its isolated ADF-H domains with G-actin. Wild-type twinfilin binds ADP-G-actin with higher affinity (K(D) = 0.05 microM) than ATP-G-actin (K(D) = 0.47 microM) under physiological ionic conditions and forms a relatively stable (k(off) = 1.8 s(-1)) complex with ADP-G-actin. Data from native PAGE and size exclusion chromatography coupled with light scattering suggest that twinfilin competes with ADF/cofilin for the high-affinity binding site on actin monomers, although at higher concentrations, twinfilin, cofilin, and actin may also form a ternary complex. By systematic deletion analysis, we show that the actin-binding activity is located entirely in the two ADF-H domains of twinfilin. Individually, these domains compete for the same binding site on actin, but the C-terminal ADF-H domain, which has >10-fold higher affinity for ADP-G-actin, is almost entirely responsible for the ability of twinfilin to increase the amount of monomeric actin in cosedimentation assays. Isolated ADF-H domains associate with ADP-G-actin with rapid second-order kinetics, whereas the association of wild-type twinfilin with G-actin exhibits kinetics consistent with a two-step binding process. These data suggest that the association with an actin monomer induces a first-order conformational change within the twinfilin molecule. On the basis of these results, we propose a kinetic model for the role of twinfilin in actin dynamics and its possible function in cells.     

The relationship of the heart rate deflection point to the ventilatory threshold in trained cyclists

The purpose of this study was to assess the relationship of the heart rate deflection point (HRDP) to the ventilatory threshold (VT) in trained cyclists. Twenty-one endurance-trained cyclists (mean +/- SD: Vo(2)max = 67.6 +/- 4.7 ml x kg x min(-1)) completed a maximal cycle ergometer test of volitional fatigue using a ramped protocol. Ventilatory variables (Ve, Vo(2), Vco(2)) and power were measured online with averages reported every 20 seconds. Heart rate (HR) was recorded every 20 seconds using a Polar monitor. VT was calculated using the excess CO(2) elimination curve. The first derivative of a logistic growth curve fit to the HR-power data produced the HRDP. No significant differences (p > 0.01) existed between HR values at HRDP (171.7 +/- 9.6 b x min(-1)) and VT (169.8 +/- 9.9 b x min(-1)) or between Vo(2) values at HRDP (53.6 +/- 4.2 ml x kg x min(-1)) and VT (52.2 +/- 4.8 ml x kg x min(-1)). But power values at HRDP (318.7 +/- 30.7 W) were significantly different (p < 0.01) from those at VT (334.8 +/- 36.7 W). There were significant relationships between HRDP and VT for the physiological variables of HR (r = 0.92, p < 0.001), Vo(2) (r = 0.72, p < 0.001), and power (r = 0.77, p < 0.001). These findings indicate that HR and Vo(2) at HRDP are not significantly different from the values at VT in trained cyclists. HR values derived from HRDP may be used to set parameters for training intensity. Variability in the speed/power-HRDP relationship across detrained/trained states may be used to evaluate training programs.     

Ecology,development and pathogenicity of Buddenbrockia plumatellae Schröder, 1910 (Myxozoa,Malacosporea) (syn. Tetracapsula bryozoides) and establishment of Tetracapsuloides n. gen. for Tetracapsula bryosalmonae

Buddenbrockia plumatellae, an enigmatic worm-like myxozoan, was observed as continuously writhing free and attached 'worms' and as free mature spores in the coelom of the freshwater bryozoans Plumatella fungosa, Hyalinella punctata, and Fredericella sp. 'Worm' numbers could double every three days. 'Worms' and spores could be expelled from colonies by external pressure. Some mature 'worms' exited actively, entraining release of free spores, and gradually ceased movement outside the host. Bryozoans sealed off infected regions of the colony. Infected colonies grew slowly, produced no statoblasts, and eventually regressed and died. Transmission was not achieved and prevalence was low. Electron microscopy of 'worms' revealed a single layer of mural cells on a fibrous basal lamina overlying four longitudinal muscle blocks and an inner sheet of two types of proliferating cells, an organization indicative of the bilaterian ancestry of the Myxozoa. Primary type A cells were attached directly by striated tubules to mural cells at positions between muscle blocks. Secondary type A cells had a secretory function. Type B cells underwent meiosis and subsequently developed to typical malacosporean myxozoan spores filling the internal cavity of the 'worms'. External tubes were formed during capsulogenesis in 'worms' from Fredericella sp. Tetracapsula bryozoides is synonymised with Buddenbrockia plumatellae and a new genus is proposed for Tetracapsula bryosalmonae.     

In Situ Microspatial Imaging Using Two-Photon and Confocal Laser Scanning Microscopy of Bacteria and Extracellular Polymeric Secretions (EPS) Within Marine Stromatolites

The combination of a hydrophilic embedding resin, Nanoplast, with fluorescent probes, and subsequent imaging using two-photon and confocal laser scanning microscopy (2P-LSM and CLSM) has allowed in imaging of the in situ microspatial arrangements of microbial cells and their extracellular polymeric secretion (EPS) within marine stromatolites. Optical sectioning by 2P-LSM and CLSM allowed imaging of endolithic cyanobacteria cells, Solentia sp., seen within carbonate sand grains. 2P-LSM allowed very clear imaging with a high resolution of bacteria using DAPI, which normally require UV excitation and reduced photo-bleaching of fluorescent probes.     

Breaking barriers through collaboration: the example of the Cell Migration Consortium

Understanding complex integrated biological processes, such as cell migration, requires interdisciplinary approaches. The Cell Migration Consortium, funded by a Large-Scale Collaborative Project Award from the National Institute of General Medical Science, develops and disseminates new technologies, data, reagents, and shared information to a wide audience. The development and operation of this Consortium may provide useful insights for those who plan similarly large-scale, interdisciplinary approaches.     

Reproductive Parameters and Maternal Investment in Mandrills (Mandrillus sphinx)

We report on 14 years of reproductive data for semifree-ranging mandrills (Mandrillus sphinx) in Gabon, and we explore relationships between female rank, age and parity, and reproductive strategies. Most births (61% of 132) occurred during the wet season in Gabon, between January and March. Female rank and parity were unrelated to the timing of parturition. Gestation lengths average 175 days (SE = ±1 day; N = 61) and were similar irrespective of female rank, parity, or sex of offspring. Birth sex ratio did not differ significantly from unity (52% male), and was unrelated to maternal rank or parity. Stillbirths and neonatal mortality tended to be more common among lower-ranking females than among either mid-ranking or dominant females. Median age at first birth is 4.71 years, at a median body mass of 7.6 kg, ca 5 years before females attain their adult body mass (median 12 kg). Age at first reproduction is significantly correlated with dominance rank, with dominant females giving birth on average 1.3 years earlier than lower-ranking females do. Interbirth intervals (IBI) average 405 days (range 184–1159 days, N = 103), and are independent of the sex of the offspring. Infant death within 6 months shortened IBI to 305 days. Increasing age and parity are also associated with short IBI, as is higher rank. Maternal rank and parity appear to influence reproductive success in female mandrills, but there is no apparent differential maternal investment by sex.     

‘And whose bright presence’ – an appreciation of Robert Hill and his reaction

The Hill reaction, its elucidation, and significance is briefly described. Hill oxidants, the role of the methemoglobin reducing factor and its relation to ferredoxin, and the part played by chloroplast envelopes are discussed. This revised version was published online in June 2006 with corrections to the Cover Date.     

Biochemistry,genetics and physiology of microbial styrene degradation

The last few decades have seen a steady increase in the global production and utilisation of the alkenylbenzene, styrene. The compound is of major importance in the petrochemical and polymer-processing industries, which can contribute to the pollution of natural resources via the release of styrene-contaminated effluents and off-gases. This is a cause for some concern as human over-exposure to styrene, and/or its early catabolic intermediates, can have a range of destructive health effects. These features have prompted researchers to investigate routes of styrene degradation in microorganisms, given the potential application of these organisms in bioremediation/biodegradation strategies. This review aims to examine the recent advances which have been made in elucidating the underlying biochemistry, genetics and physiology of microbial styrene catabolism, identifying areas of interest for the future and highlighting the potential industrial importance of individual catabolic pathway enzymes.