Graphical abstract

BACKGROUND AND PURPOSE The cholinergic agonist levamisole is widely used to treat parasitic nematode infestations. This anthelmintic drug paralyses worms by activating a class of levamisole‐sensitive acetylcholine receptors (L‐AChRs) expressed in nematode muscle cells. However, levamisole efficacy has been compromised by the emergence of drug‐resistant parasites, especially in gastrointestinal nematodes such as Haemonchus contortus. We report here the first functional reconstitution and pharmacological characterization of H. contortus L‐AChRs in a heterologous expression system. EXPERIMENTAL APPROACH In the free‐living nematode Caenorhabditis elegans, five AChR subunit and three ancillary protein genes are necessary in vivo and in vitro to synthesize L‐AChRs. We have cloned the H. contortus orthologues of these genes and expressed them in Xenopus oocytes. We reconstituted two types of H. contortus L‐AChRs with distinct pharmacologies by combining different receptor subunits. KEY RESULTS The Hco‐ACR‐8 subunit plays a pivotal role in selective sensitivity to levamisole. As observed with C. elegans L‐AChRs, expression of H. contortus receptors requires the ancillary proteins Hco‐RIC‐3, Hco‐UNC‐50 and Hco‐UNC‐74. Using this experimental system, we demonstrated that a truncated Hco‐UNC‐63 L‐AChR subunit, which was specifically detected in a levamisole‐resistant H. contortus isolate, but not in levamisole‐sensitive strains, hampers the normal function of L‐AChRs, when co‐expressed with its full‐length counterpart. CONCLUSIONS AND IMPLICATIONS We provide the first functional evidence for a putative molecular mechanism involved in levamisole resistance in any parasitic nematode. This expression system will provide a means to analyse molecular polymorphisms associated with drug resistance at the electrophysiological level.

Background-Serum response factor (SRF) is a cardiac transcription factor involved in cell growth and differentiation. We have shown, using the Cre/loxP system, that cardiac-specific disruption of SRF gene in the embryonic heart results in lethal cardiac defects. The role of SRF in adult heart is unknown. Methods and Results-We disrupted SRF in the adult heart using a heart-specific tamoxifen-inducible Cre recombinase.This disruption led to impaired left ventricular function with reduced contractility, subsequently progressing to dilated cardiomyopathy, as demonstrated by serial echocardiography, including tissue Doppler imaging. The cytoarchitecture of cardiomyocytes was altered in the intercalated disks. All mutant mice died from heart failure 10 weeks after treatment. These functional and structural defects were preceded by early alterations in the cardiac gene expression program: major decreases in mRNA levels for cardiac ␣-actin, muscle creatine kinase, and calcium-handling genes. Conclusions-SRF is crucial for adult cardiac function and integrity. We suggest that the rapid progression to heart failure in SRF mutant mice results primarily from decreased expression of proteins involved in force generation and transmission, low levels of polymerized actin, and changes in cytoarchitecture, without hypertrophic compensation. These cardiac-specific SRF-deficient mice have the morphological and clinical features of acquired dilated cardiomyopathy in humans and may therefore be used as an inducible model of this disorder.