Response of rat skin to high-dose unidirectional x-ray microbeams: a histological study

There is growing interest in evaluating microbeam radiation therapy as a potential clinical modality. Microbeam radiation therapy uses arrays of parallel, microscopically thin (<100 microm) planes of synchrotron-generated X rays (microplanar beams, or microbeams). Due to the relatively low beam energies involved in microbeam radiation therapy (a median beam energy of 120 keV was used in the present study), the dose penetration of microbeams in tissue is lower than that used in conventional radiotherapy. This lower energy necessitates using a significantly elevated dose to the skin's surface during clinical microbeam therapy to ensure an adequate dose distribution in the target tumor. The findings of the present study, using a rat skin model, indicated that the skin had an extremely high tolerance to microbeam radiation at doses considerably in excess of those that were therapeutically effective in preclinical studies. A histological study was undertaken to evaluate the biological mechanisms underlying this high tolerance. The irradiation configuration employed single-exposure, unidirectional microbeams 90 microm wide, with 300 microm beam spacing on-center. The in-beam skin-surface absorbed doses were in the range 835-1335 Gy. Monte Carlo simulations of the dose distribution indicated that the "valley" dose, i.e. the radiation leakage between adjacent microbeams, was about 2.5% of the in-beam dose. The high tolerance of the rats' skin to microbeams and the rapid regeneration of the damaged segments of skin were attributed to the surviving clonogenic cells situated between the adjacent microplanar beams. In the epidermis, clonogenic cells in the hair follicular epithelium appeared to play a key role in the regeneration process.     

Selective constraint on noncoding regions of hominid genomes

An important challenge for human evolutionary biology is to understand the genetic basis of human–chimpanzee differences. One influential idea holds that such differences depend, to a large extent, on adaptive changes in gene expression. An important step in assessing this hypothesis involves gaining a better understanding of selective constraint on noncoding regions of hominid genomes. In noncoding sequence, functional elements are frequently small and can be separated by large nonfunctional regions. For this reason, constraint in hominid genomes is likely to be patchy. Here we use conservation in more distantly related mammals and amniotes as a way of identifying small sequence windows that are likely to be functional. We find that putatively functional noncoding elements defined in this manner are subject to significant selective constraint in hominids.     

Pacific treefrogs use temporal integration to differentiate advertisement from encounter calls

Male Pacific treefrogs, Hyla regilla, use advertisement and encounter calls in their reproductive communication. Encounter calls are produced when a male hears either advertisement or encounter calls at amplitudes that exceed his aggressive threshold for that call type, and they are believed to play a role in male spacing in a chorus. Aggressive thresholds of males for advertisement and encounter calls are plastic; males resume advertisement calling (i.e. accommodate) after repeated exposure to either advertisement or encounter calls that exceed their aggressive thresholds for that call type. Presentation of one call type does not elevate a male's aggressive threshold for the other call type, indicating that discrete neural ‘channels’ exist for processing advertisement versus encounter calls. Because these calls are spectrally highly similar, it is likely that they are differentiated in the central auditory system on the basis of their different temporal structure; pulses are repeated in advertisement and encounter calls at rates of approximately 100 pulses/s and 30 pulses/s, respectively. The present study tested whether consecutive advertisement-type interpulse intervals (IPIs) are required to activate the filter for advertisement calls. Males were accommodated to synthetic stimuli that differed in the proportion of advertisement versus encounter IPIs. Aggressive thresholds of males for the encounter call and advertisement call (monophasic type) were elevated 450% and 58%, respectively, following accommodation to a stimulus that had nine of each IPI type, arranged in an alternating sequence. Aggressive thresholds for the monophasic advertisement call were elevated 151%, however, when males were accommodated with stimuli that had two sets of eight to nine consecutive advertisement IPIs; consistent with previous work, aggressive thresholds for the encounter call were not significantly elevated. Aggressive thresholds for the advertisement call are typically elevated approximately four-fold following accommodation with that call type. These findings are consistent, therefore, with the hypothesis that several consecutive advertisement IPIs are required to activate the ‘advertisement channel’; if consecutive advertisement IPIs were not required, the stimulus that consisted of the same number of advertisement and encounter IPIs should have induced comparable elevations of the aggressive thresholds of males for advertisement and encounter calls. Selective filters for the advertisement call, therefore, appear to integrate information across many consecutive ‘correct’ IPIs. This integration process may contribute to a female's call preference.Copyright 2002 The Association for the Study of Animal Behaviour. Published by Elsevier Science Ltd. All rights reserved .     

Wake dynamics and locomotor function in fishes: interpreting evolutionary patterns in pectoral fin design

The great anatomical diversification of paired fins within theActinopterygii (ray-finned fishes) can be understood as a suiteof evolutionary transformations in design. At a broad taxonomicscale, two clear trends exist in the morphology of the anteriorlysituated pectoral fins. In comparing basal to more derived clades,there are general patterns of (i) reorientation of the pectoralfin base from a nearly horizontal to more vertical inclination,and (ii) migration of the pectoral fin from a ventral to mid-dorsalbody position. As yet, the functional significance of thesehistorical trends in pectoral fin design remains largely untestedby experiment. In this paper we test the proposal that variationin pectoral fin structure has an important influence on themagnitude and orientation of fluid forces generated during maneuveringlocomotion. Using digital particle image velocimetry for quantitativewake visualization, we measure swimming forces in ray-finnedfishes exhibiting the plesiomorphic and apomorphic pectoralfin anatomy. Our experiments focus on rainbow trout (Oncorhynchusmykiss), a lower teleost with pectoral fins positioned ventrallyand with nearly horizontally inclined fin bases, and bluegillsunfish (Lepomis macrochirus), a relatively derived perciformfish with more vertically oriented pectoral fins positionedmid-dorsally on the body. In support of hypotheses arising fromour prior wake studies and previously untested models in theliterature, we find that the pectoral fins of sunfish generatesignificantly higher forces for turning and direct braking forcescloser to the center of mass of the body than the pectoral finsof trout. These results provide insight into the hydrodynamicimportance of major evolutionary transformations in pectoralfin morphology within the Actinopterygii.     

The dual-specific active site of 7,8-diaminopelargonic acid synthase and the effect of the R391A mutation

7,8-diaminopelargonic acid (DAPA) synthase (EC 2.6.1.62) is a pyridoxal phosphate (PLP)-dependent transaminase that catalyzes the transfer of the alpha-amino group from S-adenosyl-L-methionine (SAM) to 7-keto-8-aminopelargonic acid (KAPA) to form DAPA in the antepenultimate step in the biosynthesis of biotin. The wild-type enzyme has a steady-state kcat value of 0.013 s(-1), and the K(m) values for SAM and KAPA are 150 and <2 microM, respectively. The k(max) and apparent K(m) values for the half-reaction of the PLP form of the enzyme with SAM are 0.016 s(-1) and 300 microM, respectively, while those for the reaction with DAPA are 0.79 s(-1) and 1 microM. The R391A mutant enzyme exhibits near wild-type kinetic parameters in the reaction with SAM, while the apparent K(m) for DAPA is increased 180-fold. The 2.1 A crystal structure of the R391A mutant enzyme shows that the mutation does not significantly alter the structure. These results indicate that the conserved arginine residue is not required for binding the alpha-amino acid SAM, but it is important for recognition of DAPA.     

Role of iron in adriamycin biochemistry

Adriamycin forms a chelate with Fe(III) that exhibits complex redox chemistry. The drug ligand is able to directly reduce the bound Fe(III) with the concomitant production of a one-electron oxidized drug radical. This Fe(II) can reduce oxygen to hydrogen peroxide and cleave the peroxide to yield the hydroxyl radical. In addition, the drug X Fe complex can catalyze the transfer of electrons from reduced glutathione to molecular oxygen to yield superoxide, hydrogen peroxide, and hydroxyl radicals. The adriamycin X Fe complex binds to DNA to form a ternary drug X Fe X DNA complex, which is also able to catalyze the thiol-dependent reduction of oxygen and the formation of hydroxyl radical from hydrogen peroxide. As a consequence of this chemistry, the adriamycin X Fe complex can cleave DNA on the addition of glutathione or hydrogen peroxide. Although less well defined, the adriamycin X Fe complex can bind to cell membranes and cause oxidative destruction of these membranes in the presence of thiols or hydrogen peroxide.     

Assessing the spatial variability of density dependence in waterfowl populations

Population models commonly assume that the demographic parameters are spatially invariant, but there is considerable evidence that population growth rate (r) and the strength of density dependence (β) can vary over a species' range. To address this issue we developed a spatially explicit Gompertz population model based on the spatially varying coefficients approach to assess the spatial variation in population drivers. The model was fit to spatially stratified time series population estimates of the mallard Anas platyrhynchos in western North America. We included precipitation during the previous year and spring maximum temperature in the current year as environmental factors in the density dependent population model. Because density dependent models can give biased estimates for time series of abundance data, we fit a naïve model without informative priors and a model where we constrained the mean and variance of r to biologically realistic values that were derived via a comparative demography approach. In the naïve model, r and β were not separately identifiable and their values were overestimated, leading to unrealistic population growth. The naïve model also implied spatial variation in population r and the return time to equilibrium [1?(– β)] across the survey area. In contrast, in the informative model, r and the return time to equilibrium did not vary markedly among populations and were generally equal across populations. The effects of the climatic factors were similar across models. Population growth rates in the Prairie‐pothole region were positively correlated with precipitation, while in Alaska rates were positively correlated with spring temperature. Although it has been argued in the past that adding ecological realism could help avoid the pitfalls associated with density dependent models, our results demonstrate that imposing constraints on the population parameters is still the best course of action.     

Orchid Fleck Virus Infecting Orchids in Paraguay: First Report and Use of Degenerate Primers for its Detection

The presence of Orchid fleck virus (OFV) in Paraguay was confirmed in orchid plants collected during a survey carried out in 2013. Leaves displayed ringspot and fleck symptoms, and in infected tissues, non‐enveloped, short, rodlike viral particles were observed. Partial OFV N and L genes were amplified using specific and degenerate primers, respectively; the nucleotide sequences demonstrated high identities (98%) with other OFV isolates. Degenerate primers for the L gene were designed considering conserved regions within all of the available OFV sequences and those from the closely related isolates citrus leprosis virus nuclear type (CiLV‐N) and citrus necrotic spot virus. Degenerate primers were also successfully used for the detection of CiLV‐N from infected citrus samples.