Does the invasive horse-chestnut leaf mining moth, <Emphasis Type="Italic">Cameraria ohridella</Emphasis>, affect the native beech leaf mining weevil, <Emphasis Type="Italic">Orchestes fagi</Emphasis>, through apparent competition?

Apparent competition, through the action of shared natural enemies, is frequently suggested as a possible mechanism underlying the impact of invasive alien species on native species, but examples are rare, particularly in insects. A previous study showed that the beech leaf mining weevil, Orchestes fagi, was significantly less abundant close to horse-chestnut trees infested by the invasive horse-chestnut leaf mining moth, Cameraria ohridella, compared to control sites. Apparent competition through the sharing of natural enemies was proposed as a potential mechanism underlying this effect. To test the occurrence of apparent competition between the two leaf miner species, three observational studies and one experimental manipulation were carried out in Switzerland during 3 years. The total mortality, parasitism, predation and parasitoid diversity of larvae and pupae of O. fagi were compared between sites with and without horse-chestnut trees severely attacked by C. ohridella. Total mortality and predation rates of O. fagi were not significantly different between sites with and sites without C. ohridella. Despite a large overlap between the parasitoid complexes of the two leaf miners, parasitism of O. fagi was found to be positively influenced by the presence of horse-chestnuts infested by C. ohridella in only one of the four studies and only for 1 year. Similarly, parasitoid diversity was not higher near infested horse-chestnut trees compared to control sites. Thus, little evidence for apparent competition was found. Possible reasons, including possible insufficiencies in the experimental circumstances and design, are discussed.     

Biomimetic divalent ligands for the acute disruption of synaptic AMPAR stabilization

The interactions of the AMPA receptor (AMPAR) auxiliary subunit Stargazin with PDZ domain-containing scaffold proteins such as PSD-95 are critical for the synaptic stabilization of AMPARs. To investigate these interactions, we have developed biomimetic competing ligands that are assembled from two Stargazin-derived PSD-95/DLG/ZO-1 (PDZ) domain-binding motifs using 'click' chemistry. Characterization of the ligands in vitro and in a cellular FRET-based model revealed an enhanced affinity for the multiple PDZ domains of PSD-95 compared to monovalent peptides. In cultured neurons, the divalent ligands competed with transmembrane AMPAR regulatory protein (TARP) for the intracellular membrane-associated guanylate kinase resulting in increased lateral diffusion and endocytosis of surface AMPARs, while showing strong inhibition of synaptic AMPAR currents. This provides evidence for a model in which the TARP-containing AMPARs are stabilized at the synapse by engaging in multivalent interactions. In light of the prevalence of PDZ domain clusters, these new biomimetic chemical tools could find broad application for acutely perturbing multivalent complexes.     

Characterization of the Mycobacterium avium subsp. paratuberculosis laminin-binding/histone-like protein (Lbp/Hlp) which reacts with sera from patients with Crohn's disease

Mycobacterium avium subsp. paratuberculosis (Map) causes a chronic enteric disease in ruminants, called paratuberculosis or Johne's disease. The current model proposes that after ingestion by the host, Map crosses the intestinal barrier via internalization by the M cells. Experimental observations suggest, however, that Map may also transcytose the intestinal wall via the enterocytes, but the mechanisms involved in this process remain poorly understood. Cytoadherence assays performed on epithelial cells with Map revealed that the addition of laminin to the cell culture increases adhesion. A Map protein was isolated by heparin-Sepharose chromatography and identified as a laminin-binding protein like. The gene encoding this protein named Lbp/Hlp was identified in the Map genome sequence at locus MAP3024 (annotated Hup B). The deduced Map Lbp/Hlp amino acid sequence reveals 80% identity with that reported for other mycobacteria. The C-terminal domain involved in adhesion is mainly composed of arginine and lysine residues modified by methylation. In vitro tests demonstrated that recombinant Lbp/Hlp binds laminin, heparin, collagen and epithelial cells. Interestingly, we found that this adhesin corresponds to the antigen described as the target of pANCA and serum antibodies of patients with Crohn's disease.     

Role of the gap junctions in the contractile response to agonists in pulmonary artery from two rat models of pulmonary hypertension

Background

Pulmonary hypertension (PH) is characterized by arterial vascular remodelling and alteration in vascular reactivity. Since gap junctions are formed with proteins named connexins (Cx) and contribute to vasoreactivity, we investigated both expression and role of Cx in the pulmonary arterial vasoreactivity in two rat models of PH.

Methods

Intrapulmonary arteries (IPA) were isolated from normoxic rats (N), rats exposed to chronic hypoxia (CH) or treated with monocrotaline (MCT). RT-PCR, Western Blot and immunofluorescent labelling were used to study the Cx expression. The role of Cx in arterial reactivity was assessed by using isometric contraction and specific gap junction blockers. Contractile responses were induced by agonists already known to be involved in PH, namely serotonin, endothelin-1 and phenylephrine.

Results

Cx 37, 40 and 43 were expressed in all rat models and Cx43 was increased in CH rats. In IPA from N rats only, the contraction to serotonin was decreased after treatment with ^37-43Gap27, a specific Cx-mimetic peptide blocker of Cx 37 and 43. The contraction to endothelin-1 was unchanged after incubation with ⁴⁰Gap27 (a specific blocker of Cx 40) or ^37-43Gap27 in N, CH and MCT rats. In contrast, the contraction to phenylephrine was decreased by ⁴⁰Gap27 or ^37-43Gap27 in CH and MCT rats. Moreover, the contractile sensitivity to high potassium solutions was increased in CH rats and this hypersensitivity was reversed following ^37-43Gap27 incubation.

Conclusion

Altogether, Cx 37, 40 and 43 are differently expressed and involved in the vasoreactivity to various stimuli in IPA from different rat models. These data may help to understand alterations of pulmonary arterial reactivity observed in PH and to improve the development of innovative therapies according to PH aetiology.