Neutron RBEs for mouse skin at low doses per fraction

The effect of low doses of 240 kVp X rays or of 3 MeV neutrons has been investigated using skin reactions on mouse feet as the biological system. Eight or nine repeated small doses of radiation were used, followed by graded "top-up" doses to bring the reactions into a detectable range. By comparing dose-response curves, the RBE has been determined for neutron doses per fraction ranging from 0.25-1.0 Gy. The data are consistent with a limiting RBE of between 7 and 10 at very low doses. A review of other published RBE values for low doses per fraction shows a wide range of RBEs . Very few studies show a plateau value for the RBE. These findings are more consistent with dose-response data that fit a linear-quadratic model than with a multitarget single-hit model.     

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ObjectivesTo identify whether psychiatric disturbance in parentally bereaved children and surviving parents is related to service provision.DesignProspective case-control study.SettingTwo adjacent outer London health authorities. Participants45 bereaved families with children aged 2 to 16 years.ResultsParentally bereaved children and surviving parents showed higher than expected levels of psychiatric difficulties. Boys were more affected than girls, and bereaved mothers had more mental health difficulties than bereaved fathers. Levels of psychiatric disturbance in children were higher when parents showed probable psychiatric disorder. Service provision related to the age of the children and the manner of parental death. Children under 5 years of age were less likely to be offered services than older children even though their parents desired it. Children were significantly more likely to be offered services when the parent had committed suicide or when the death was expected. Children least likely to receive service support were those who were not in touch with services before parental death.ConclusionsService provision was not significantly related to parental wishes or to level of psychiatric disturbance in parents or children. There is a role for general practitioners and primary care workers in identifying psychologically distressed surviving parents whose children may be psychiatrically disturbed, and referring them to appropriate services.

Key messages

• Parentally bereaved children show high levels of psychological disturbance, with boys being more vulnerable than girls
• Surviving mothers show more psychiatric morbidity than surviving fathers
• Psychological distress in bereaved parents is associated with psychological difficulties in their children
• Service provision for bereaved children is not determined by mental health difficulties in either parents or children, or by parental wishes; it is influenced only by the manner of parental death and the age of the child
• The mismatch between need and service provision indicates a role for general practitioners and primary care workers in identifying distressed or disturbed families in need of public or voluntary service help

     

Stochastic processes influence stationary-phase decisions in Bacillus subtilis

It has recently been proposed that phenotypic variation in clonal populations of bacterial species results from intracellular "noise," i.e., random fluctuations in levels of cellular molecules, which would be predicted to be insensitive to selective pressure. To test this notion, we propagated five populations of Bacillus subtilis for 5,000 generations with selection for one phenotype: the decision to sporulate. In support of the noise hypothesis, we report that none of the populations responded to selection by improving their efficiency of sporulation, indicating that intracellular noise is independent of heritable genotype.     

Alternative N-terminal regions of Drosophila myosin heavy chain tune muscle kinetics for optimal power output

We assessed the influence of alternative versions of a region near the N-terminus of Drosophila myosin heavy chain on muscle mechanical properties. Previously, we exchanged N-terminal regions (encoded by alternative exon 3s) between an embryonic (EMB) isoform and the indirect flight muscle isoform (IFI) of myosin, and demonstrated that it influences solution ATPase rates and in vitro actin sliding velocity. Because each myosin is expressed in Drosophila indirect flight muscle, in the absence of other myosin isoforms, this allows for muscle mechanical and whole organism locomotion assays. We found that exchanging the flight muscle specific exon 3 region into the embryonic isoform (EMB-3b) increased maximum power generation (P(max)) and optimal frequency of power generation (f(max)) threefold and twofold compared to fibers expressing EMB, whereas exchanging the embryonic exon 3 region into the flight muscle isoform (IFI-3a) decreased P(max) and f(max) to approximately 80% of IFI fiber values. Drosophila expressing IFI-3a exhibited a reduced wing beat frequency compared to flies expressing IFI, which optimized power generation from their kinetically slowed flight muscle. However, the slower wing beat frequency resulted in a substantial loss of aerodynamic power as manifest in decreased flight performance of IFI-3a compared to IFI. Thus the N-terminal region is important in tuning myosin kinetics to match muscle speed for optimal locomotory performance.     

Mutations that affect flightin expression in Drosophila alter the viscoelastic properties of flight muscle fibers

Striated muscles across phyla share a highly conserved sarcomere design yet exhibit broad diversity in contractile velocity, force, power output, and efficiency. Insect asynchronous flight muscles are characterized by high-frequency contraction, endurance, and high-power output. These muscles have evolved an enhanced delayed force response to stretch that is largely responsible for their enhanced oscillatory work and power production. In this study we investigated the contribution of flightin to oscillatory work using sinusoidal analysis of fibers from three flightless mutants affecting flightin expression: 1) fln⁰, a flightin null mutant, 2) Mhc¹³, a myosin rod point mutant with reduced levels of flightin, and 3) Mhc⁶, a second myosin rod point mutant with reduced levels of phosphorylated flightin. Fibers from the three mutants show deficits in their passive and dynamic viscoelastic properties that are commensurate with their effect on flightin expression and result in a significant loss of oscillatory work and power. Passive tension and passive stiffness were significantly reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. The dynamic viscous modulus was significantly reduced in the three mutants, whereas the dynamic elastic modulus was reduced in fln⁰ and Mhc¹³ but not in Mhc⁶. Tension generation under isometric conditions was not impaired in fln⁰. However, when subjected to sinusoidal length perturbations, work-absorbing processes dominated over work-producing processes, resulting in no net positive work output. We propose that flightin is a major contributor to myofilament stiffness and a key determinant of the enhanced delayed force response to stretch in Drosophila flight muscles. flight muscles; muscle mutants; myosin     

The M. tuberculosis antigen 85 complex and mycolyltransferase activity

AIMS: The antigen 85 complex (Ag85) from Mycobacterium tuberculosis consists of three abundantly secreted proteins (FbpA, FbpB and FbpC2) which play a key role in the pathogenesis of tuberculosis and also exhibit cell wall mycolyltransferase activity. A related protein with similarity to the Ag85 complex was recently annotated in the M. tuberculosis genome as FbpC1. An investigation was carried out to determine whether FbpC1 may also possess mycolyltransferase activity, a characteristic feature of the Ag85 complex. METHODS AND RESULTS: Heterologous expression of FbpA, FbpC1 and FbpC2 was performed in Escherichia coli. Recombinant proteins were purified under non-denaturating conditions and used in an in vitro mycolyltransferase assay. CONCLUSIONS: In contrast to FbpA and FbpC2, recombinant FbpC1 did not possess in vitro mycolyltransferase activity and was not recognized by two monoclonal antibodies to the native Ag85. SIGNIFICANCE AND IMPACT OF THE STUDY: Mycolyltransferase activity is restricted to FbpA, FbpbB and FbpC2 only; the actual function of FbpC1 remains to be established.     

Population structure and food habits of white crappie Pomoxis annularis Rafinesque in a turbid Oklahoma reservoir

We assessed population structure and food habits of white crappie Pomoxis annuluris Rafinesque in Lake Carl Blackwell, a turbid reservoir in north-central Oklahoma, U.S.A. White crappie [ n = 8549; total length ( t.l. ) mean = 147 mm, s.d. = 28 mm, range = 73–445 mm] were collected with gillnets, frame nets, and hoop nets. Proportional stock density was 2, as 97% of the fish were under 200 mm t.l . Relative stock density was 96, 2, 1, and 1 for 'stock-quality', 'quality-preferred', 'preferred-memorable', and 'memorable-trophy' lengths. Total annual mortality rate was 54% for fish older than 2 years. Growth was poor and lower than the Oklahoma-Arkansas regional averages ( P <0.01). Relative weights were 79, 86, 106, 109, and 123 for fish in the stock-quality, quality-preferred, preferred-memorable, memorable-trophy, and trophy size categories. Ephemeroptera nymphs were an important dietary component for fish 150 mm t.l. or smaller. Gizzard shad Dorosoma cepedianum (Lesueur) was a major forage item, especially for fish greater than 150 mm t.l. ( P <0.01). Empirical information on prey availability indicates that the white crappie population is forage limited and that gizzard shad are not available in appropriate sizes or sufficient numbers to sustain the predator population. Poor fish condition, slow growth, and high mortality are probably the result of inadequate forage.     

Effect of population density and feeding rate on the fathead minnow (Pimephales promelas)

Juvenile fathead minnows ( Pimephales promelas ) were stocked in tanks at different densities and different ration levels, in two experiments, to determine effects on final population density, growth and fecundity. Length and weight of fish increased with increased food availability. Egg size was exponentially related to growth and perhaps directly to ration level. High population density appeared to limit growth and gamete development regardless of food abundance. Additionally, water volume appeared to limit numbers (tolerance density) of fish which can be supported in a specific volume of water.