acr-23 Encodes a monepantel-sensitive channel in Caenorhabditis elegans.

Monepantel is a member of the recently identified class of anthelmintics known as the amino-acetonitrile derivatives (AADs). Monepantel controls all major gastro-intestinal nematodes in sheep including those that are resistant to the classical anthelmintics. Previous studies have shown that the Caenorhabditis elegans acr-23 and the Haemonchus contortus Hco-mptl-1 genes may be prominent targets of monepantel. With this discovery it became possible to investigate the mode of action of monepantel in nematodes at the molecular level. In the present study, we show that a C. elegans mutant acr-23 strain is fully rescued by expressing the wild-type acr-23 gene. Moreover, we present a new mutant allele, and characterize acr-23 alleles genetically. We also show that acr-23 is expressed in body wall muscle cells, and provide therefore a possible explanation for the paralysis caused by monepantel. Furthermore, genetic evidence suggests that the chaperone RIC-3 is required for expression of full monepantel resistance. Finally, we present reconstitution of the C. elegans ACR-23 receptor in Xenopus laevis oocytes and provide direct evidence of its modulation by monepantel. Conversely, co-injection of the chaperone RIC-3 had no impact for channel reconstitution in X. laevis oocytes. These results reinforce the involvement of the ACR-23 family in the mode of action of monepantel and advance our understanding of this new class of anthelmintics.

The sperm-oocyte switch in the C. elegans hermaphrodite is controlled through steady-state levels of the fem-3 mRNA.

Post-transcriptional control regulates many aspects of germline development in the Caenorhabditis elegans hermaphrodite. This nematode switches from spermatogenesis to oogenesis and is, therefore, capable of self-fertilization. This sperm-oocyte switch requires 3' UTR-mediated repression of the fem-3 mRNA. Loss of fem-3 repression results in continuous spermatogenesis in hermaphrodites. Although several factors regulating fem-3 have been identified, little is known about the mechanisms that control fem-3. Here, we investigate the steady-state levels of the fem-3 transcript and the expression pattern of its protein product. We show that FEM-3 is exclusively present in germ cells that are committed to spermatogenesis. We found that in fem-3(gf)/+ heterozygotes, mutant fem-3 gain-of-function transcripts are more abundant than their wild-type counterpart. Furthermore, we show that the penetrance of the fem-3(gf) allele correlates with inefficient FBF binding and extended poly(A) tail size of fem-3 mRNAs. Finally, we show that wild-type and gain-of-function mutated fem-3 mRNAs associate equally well with polyribosomes. We propose that the fem-3 mRNA is regulated through stabilization rather than through translatability.