The molecular targets of ivermectin and lotilaner in the human louse Pediculus humanus humanus: New prospects for the treatment of pediculosis

Control of infestation by cosmopolitan lice (Pediculus humanus) is increasingly difficult due to the transmission of parasites resistant to pediculicides. However, since the targets for pediculicides have no been identified in human lice so far, their mechanisms of action remain largely unknown. The macrocyclic lactone ivermectin is active against a broad range of insects including human lice. Isoxazolines are a new chemical class exhibiting a strong insecticidal potential. They preferentially act on the γ-aminobutyric acid (GABA) receptor made of the resistant to dieldrin (RDL) subunit and, to a lesser extent on glutamate-gated chloride channels (GluCls) in some species. Here, we addressed the pediculicidal potential of isoxazolines and deciphered the molecular targets of ivermectin and the ectoparasiticide lotilaner in the human body louse species Pediculus humanus humanus. Using toxicity bioassays, we showed that fipronil, ivermectin and lotilaner are efficient pediculicides on adult lice. The RDL (Phh-RDL) and GluCl (Phh-GluCl) subunits were cloned and characterized by two-electrode voltage clamp electrophysiology in Xenopus laevis oocytes. Phh-RDL and Phh-GluCl formed functional homomeric receptors respectively gated by GABA and L-glutamate with EC₅₀ values of 16.0 μM and 9.3 μM. Importantly, ivermectin displayed a super agonist action on Phh-GluCl, whereas Phh-RDL receptors were weakly affected. Reversally, lotilaner strongly inhibited the GABA-evoked currents in Phh-RDL with an IC₅₀ value of 40.7 nM, whereas it had no effect on Phh-GluCl. We report here for the first time the insecticidal activity of isoxazolines on human ectoparasites and reveal the mode of action of ivermectin and lotilaner on GluCl and RDL channels from human lice. These results emphasize an expected extension of the use of the isoxazoline drug class as new pediculicidal agents to tackle resistant-louse infestations in humans.     

Turnover of plant lineages shapes herbivore phylogenetic beta diversity along ecological gradients

Understanding drivers of biodiversity patterns is of prime importance in this era of severe environmental crisis. More diverse plant communities have been postulated to represent a larger functional trait‐space, more likely to sustain a diverse assembly of herbivore species. Here, we expand this hypothesis to integrate environmental, functional and phylogenetic variation of plant communities as factors explaining the diversity of lepidopteran assemblages along elevation gradients in the Swiss Western Alps. According to expectations, we found that the association between butterflies and their host plants is highly phylogenetically structured. Multiple regression analyses showed the combined effect of climate, functional traits and phylogenetic diversity in structuring butterfly communities. Furthermore, we provide the first evidence that plant phylogenetic beta diversity is the major driver explaining butterfly phylogenetic beta diversity. Along ecological gradients, the bottom up control of herbivore diversity is thus driven by phylogenetically structured turnover of plant traits as well as environmental variables.     

Carbohydrate moieties of rat MHC class I antigens

The rat major histocompatibility complex class I antigens RT1.A^u and RT1.E^u from the u haplotype and RT1.Aⁿ from the n haplotype were labeled with ¹⁴C-asparagine or with ³H-fucose, mannose, galactose, and N-acetylglucosamine. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis showed complete removal of radioactivity from the sugar-labeled antigen heavy chains by digestion with glycopeptidase F, an enzyme that removes N-linked glycans completely. High performance liquid chromatography analysis of the tryptic digests of the mixed sugar-labeled and asparagine-labeled antigens demonstrated that all the sugar-labeled peptides were coincident with asparagine-labeled peptides. The Aⁿ antigen showed three glycopeptides, each of which had different amounts of sugar radioactivity. The antigens A^u and E^u showed two glycopeptides with different amounts of radioactivity but at identical positions in the two antigens. Antigen E^u had an additional glycopeptide with a lower amount of radioactivity. The positions of the glycopeptides from the A^u and E^u antigens were different from those of the Aⁿ antigen. The peptide profiles of the ¹⁴C-asparagine-labeled A^u and E^u antigens demonstrated distinct differences between the molecules. The results of this study show that: (a) all the glycans on rat class I antigens are N-linked, as they are on H-2 and HLA class I antigens; (b) there are compositional differences among the glycans in each of the three antigens; (c) the glycosylation pattern of the rat class I antigens is similar to that of the mouse class I antigens, which contain two or three glycans, in contrast to that of the human class I antigens, which contain only one glycan; and (d) the antigens A^u and E^u from the same haplotype are more closely related to each other than they are to the Aⁿ antigen.     

Development of a yeast system to assay mutational specificity

We have developed a system wherein DNA alterations occurring in a target gene in the yeast Saccharomyces cerevisiae can be determined by DNA sequencing. The target gene, SUP4-o, an ochre suppressor allele of a yeast tyrosine tRNA gene, has been inserted into a shuttle vector (YCpMP2) which is maintained in yeast at a copy number of one per cell Mutations in SUP4-o are selected by virtue of their inactivation of suppressor activity. Rapid DNA preparations from these mutants are used to transform an appropriate bacterial strain. Since YCpMP2 also carries the M13 phage replication origin, superinfection of bacterial cells containing the plasmid with wild-type M13 phage yields single stranded YCpMP2 DNA suitable for dideoxynucleotide chain termination sequencing. We have used this system to examine mutations arising spontaneously in the SUP4-o gene. The spontaneous mutants occurred at a frequency of 3.2 X 10(-6)/viable cell, corresponding to a rate of 2.7 X 10(-7) events/cell division. Following bacterial transformation, 16% of the recovered plasmids tested displayed altered gel mobility consistent with loss of significant portions of the plasmid. Hybridization analysis of total yeast DNA and use of purified YCpMP2 revealed that these very large deletions were not generated in yeast but were associated with bacterial transformation. Among the SUP4-o mutants analyzed by DNA sequencing, we identified each type of single base pair substitution (transitions and transversions), small deletions of varying length (1-32 base pairs) and more extensive deletions of undetermined size. These results demonstrate that the SUP4-o system can be used to detect various types of mutation at numerous sites in a single eukaryotic gene and to characterize the DNA sequence changes responsible for the mutations selected.     

Ribosomal gene amplification does not occur in the oocytes of Locusta migratoria

It has been suggested that Locusta migratoria amplifies its ribosomal RNA genes in the growing oocytes (Kunz (1967) Chromosoma20, 332–370). Cloned ribosomal DNA of L. migratoria was used to analyze rDNA structure and number. The rDNA is localized on three chromosome pairs in six nucleolus organizers. It was found that all structural variants of the rRNA genes which have been described previously are represented in the same relative amounts in DNA from isolated oocytes as in somatic cells. Furthermore, the rRNA gene number is not increased in oocyte DNA, i.e., amplification does not occur. Therefore, the large number of multiple nucleoli seen in the growing oocytes has to be interpreted as the fully extended and fully active set of chromosomal rRNA genes. The total rRNA gene number was determined by dot blot hybridization to be about 3300 genes/haploid genome.     

Molecular diagnosis of Duchenne and Becker muscular dystrophies. Current data

Carrier diagnosis and prenatal diagnosis of Duchenne's muscular dystrophy (DMD) and Becker's muscular dystrophy (BMD) has become possible using some twenty RFLPs detected by more than a dozen Xp21 probes that are either intragenic or flanking the disease locus. Results from familial studies on 88 DMD and BM families stress important considerations concerning a priori and final risks, individuals necessary for the identification of the phase, and the different strategies that can be applied, regardless of whether the study concerns an on-going pregnancy or a carrier-status determination, and whether the patient is at high or low risk. Finally, multiple sources of difficulties in interpreting the results depend on a) the occurrence of new mutations that must be traced; b) the existence of meiotic recombination; c) the necessity, in some instances, of relying upon the sole identification of the paternal X. These considerations emphasize the characteristics and the important limitations of this type of methodology.     

TheRT1.G locus in the rat encodes a Qa/TL-like antigen

A new antigenic system in the rat homologous to theQa/TL antigen system in the mouse has been characterized. It was detected by antibodies raised in donor-recipient combinations that were matched for theRT1. A, B, D, E loci in the major histocompatibility complex (MHC): (R11×BN)F₁ anti-BN.1L(LEW), (R18×BN)F₁ anti-BN.1L, and BN.1LV1(F344) anti-BN.1L. Absorption analyses using these antisera and a variety of inbred, congenic and recombinant strains identified three alleles,RT1.G ^a ,G ^b ,G ^c , of whichG ^c is a null allele. The strain distribution of these alleles was determined, using 37 strains of rats representative of all of the prototypic haplotypes and a number of congenic and recombinant strains. The use of the congenic and recombinant strains showed that theRT1.G locus was linked to the MHC and that the most probable gene order wasA-E-G. Testcross analysis showed that the map distance betweenA andG was 1.4 cM(4/285 recombinants). The RT1.G antigen has a heavy chain ofM _r 46 000 and is present on both T and B cells.