Sequence differences between histones of procyclic Trypanosoma brucei brucei and higher eukaryotes

Four histones, a, b, c, d from procyclic Trypanosoma brucei brucei, which show similarities with the amino acid composition of the core histones H3, H2A, H2B and H4, were isolated and cleaved with Endoproteinase Glu-C. The fragments were separated by FPLC reversed phase chromatography and a subset of the fragments (a5, a9, b6, c8, d3, d9, d11) was subjected to sequence analysis. A 54-71% identity was found in the sequences of the fragment c8 and the C-terminal half of H2B and of three fragments of protein d covering the N-terminal half as well as the C-terminal region of H4. The amino acid sequence of the fragment a9 showed a 57 and 54% identity with H3 sequences of Saccharomyces cerevisiae and Xenopus laevis. Neither the a5 nor the b6 sequence could be aligned with histone sequences of other eukaryotes. The significant differences of 21-48% between the T. b. brucei, histone sequences and those of calf thymus histones, which are more pronounced than the differences of Tetrahymena pyriformis and the higher eukaryote, resulted partially from replacements of amino acids with different properties and indicate specific patterns of histone-histone and/or histone-DNA contact sites in the nucleosome of T. b. brucei. These differences, together with the lack of a functional histone H1, may be sufficient to explain the lack of a salt-dependent formation of the nucleosome filament into the 30 nm fibre, which reflects alternative methods of organizing and processing the genetic information in the nucleus of the protozoan parasite and which may be of chemotherapeutic significanc

Determination of Acaricide Resistance in Rhipicephalus (Boophilus) microplus (Acari: Ixodidae) Field Populations of Argentina, South Africa, and Australia With the Larval Tarsal Test

Infestations with ticks have an important economic impact on the cattle industry worldwide and resistance to acaricides has become a widespread phenomenon. To optimize their treatment strategy, farmers need to know if and against which classes potential acaricide-resistance does occur. Bioassays are used to assess the resistance level and pattern of Rhipicephalus (Boophilus) microplus populations. The objective of the current study was to assess the susceptibility of field populations originating from Argentina (8), South Africa (3), and Australia (2) using the Larval Tarsal Test. Nine acaricidal compounds from five major classes were tested: organosphosphates, synthetic pyrethroids (SP), macrocyclic lactones, phenylpyrazols, and amidines. The resistance ratios at concentrations inducing 50 and 90% mortality were used to detect established and emerging resistance. This study confirmed the newly reported presence of amitraz resistance in populations from Argentina. In addition, resistance to SP appeared to be widespread (88%) in the Argentinean farms, which had been selected based on the observation of lack of treatment efficacy by farmers. In South Africa one of the three populations was found to be resistant to SP and to a phenylpyrazol compound (pyriprol). Furthermore, resistance to organosphosphates and SP was observed in Australia. Finally, the Larval Tarsal Test proved to be a suitable test to evaluate the susceptibility of R. microplus field populations to the most relevant acaricidal classe

Genetically discrete populations of Trypanosoma congolense from livestock on the Kenyan coast

Twenty-seven stocks of Nannomonas trypanosomes isolated from livestock in 1982 on a ranch at Kilifi on the Kenyan coast were characterized by isoenzyme electrophoresis and by the abilities of the parasite's DNA to hybridize to two repetitive sequence DNA probes. Allthe Kilifi stocks which were examined had isoenzyme patterns which were markedly different from the 75 patterns previously described from 78 stocks of Trypanosoma congolense. On average only 15% of the enzyme bands present in the Kilifi stocks were present in those stocks of T. congolense which had previously been surveyed for isoenzymes. The DNA from all the Kilifi stocks which had been examined for isoenzymes hybridized with only the repetitive sequence probe isolated from a clone of a Kilifi stock. In contrast, the DNA from all 27 Kilifi stocks failed to hybridize with a repetitive sequence probe isolated from a clone from a different stock of T. congolense. Thus, the trypanosomes in all the Kilifi stocks examined were both phenotypically and genotypically discrete. These genetically discrete trypanosomes have also been detected in 2 stocks isolated from livestock from another location on the Kenyan coast. The results show that there is a wide range of genetic heterogeneity within the trypanosomes currently classified as T. congolense. We suggest that the limits of this genetic heterogeneity could represent incipient speciatio

Distribution patterns of three sodium channel mutations associated with pyrethroid resistance in Rhipicephalus (Boophilus) microplus populations from North and South America, South Africa and Australia

AbstractResistance to synthetic pyrethroids (SP) in the cattle tick Rhipicephalus (Boophilus) microplus is widespread throughout its distribution area. Three single nucleotide substitutions identified in Domains II and III of the sodium channel gene of R. (B.) microplus are known to be associated with target site pyrethroid resistance. We developed a multiplex PCR using allele-specific primers to amplify wild type or mutated genotypes of the three mutations simultaneously. This assay was used to screen tick samples originating from Brazil, Argentina, Mexico, South Africa and Australia whose phenotype to flumethrin and cypermethrin had been determined by the use of the Larval Tarsal test (LTT) or the Larval Packet Test (LPT). These mutations were found to have distinct geographical distributions and result in different resistance phenotypes. The L64I Domain II mutation conferring resistance to several SP compounds was found in all the Brazilian, Argentinean and Australian populations and in one South African population, with frequencies between 38% and 100% in flumethrin and cypermethrin resistant populations. In contrast, this mutation was not found in samples from Mexico, while the Domain III mutation was found exclusively in this country. The G72V Domain II flumethrin-specific mutation was found in a single Australian population, with a very low resistant allele frequency (3%). The homozygous resistant RR genotype of the L64I Domain II mutation correlated significantly with the survival rates at the discriminating doses of flumethrin and cypermethrin. This survey shows the widespread distribution of the L64I Domain II mutation and provides evidence of its geographic separation from the Domain III mutation

Cosmic magnetic fields from velocity perturbations in the early Universe

We show, using a covariant and gauge-invariant charged multifluid perturbation scheme, that velocity perturbations of the matter-dominated dust Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of cosmic magnetic fields. Moreover, using cosmic microwave background (CMB) constraints, it is argued that these fields can reach strengths of between 10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them plausible seed field candidates.Comment: 11 pages, 1 figure, IOP style, minor changes and typos correcte

On pelvic reference lines and the MR evaluation of genital prolapse: a proposal for standardization using the Pelvic Inclination Correction System

Five midsagittal pelvic reference lines have been employed to quantify prolapse using MRI. However, the lack of standardization makes study results difficult to compare. Using MRI scans from 149 women, we demonstrate how use of existing reference lines can systematically affect measurements in three distinct ways: in oblique line systems, distances measured to the reference line vary with antero-posterior location; soft issue-based reference lines can underestimate organ movement relative to the pelvic bones; and systems defined relative to the MR scanner are affected by intra- and interindividual differences in the pelvic inclination angle at rest and strain. Thus, we propose a standardized approach called the Pelvic Inclination Correction System (PICS). Based on bony structures and the body axis, the PICS system corrects for variation in pelvic inclination, at rest of straining, and allows for the standardized measurement of organ displacement in the direction of prolaps

Perfect magnetohydrodynamics as a field theory

We propose the generally covariant action for the theory of a self-coupled complex scalar field and electromagnetism which by virtue of constraints is equivalent, in the regime of long wavelengths, to perfect magnetohydrodynamics (MHD). We recover from it the Euler equation with Lorentz force, and the thermodynamic relations for a prefect fluid. The equation of state of the latter is related to the scalar field's self potential. We introduce 1+3 notation to elucidate the relation between MHD and field variables. In our approach the requirement that the scalar field be single valued leads to the quantization of a certain circulation in steps of $\hbar$; this feature leads, in the classical limit, to the conservation of that circulation. The circulation is identical to that in Oron's generalization of Kelvin's circulation theorem to perfect MHD; we here characterize the new conserved helicity associated with it. We also demonstrate the existence for MHD of two Bernoulli-like theorems for each spacetime symmetry of the flow and geometry; one of these is pertinent to suitably defined potential flow. We exhibit the conserved quantities explicitly in the case that two symmetries are simultaneously present, and give examples. Also in this case we exhibit a new conserved MHD circulation distinct from Oron's, and provide an example.Comment: RevTeX, 16 pages, no figures; clarifications added and typos corrected; version to be published in Phys. Rev.

Primordial magnetic fields from second-order cosmological perturbations: Tight coupling approximation

We explore the possibility of generating large-scale magnetic fields from second-order cosmological perturbations during the pre-recombination era. The key process for this is Thomson scattering between the photons and the charged particles within the cosmic plasma. To tame the multi-component interacting fluid system, we employ the tight coupling approximation. It is shown that the source term for the magnetic field is given by the vorticity, which signals the intrinsically second-order quantities, and the product of the first order perturbations. The vorticity itself is sourced by the product of the first-order quantities in the vorticity evolution equation. The magnetic fields generated by this process are estimated to be $\sim 10^{-29}$Gauss on the horizon scale at the recombination epoch. Although our rough estimate suggests that the current generation mechanism can work even on smaller scales, more careful investigation is needed to make clear whether it indeed works in a wide range of spatial scales.Comment: 10pages, minor corrections, accepted for publication in Class. Quant. Gra