Yoshida M et al. (2001) Biochem Biophys Res Commun "Important role of junctophilin in nematode motor function."

Yoshida M, Sugimoto A, Takeshima H, Ohshima Y

[Biochem Biophys Res Commun, 2001]

Junctional complexes between the plasma membrane and endoplasmic/sareoplasmic reticulum are shared by excitable cells and seem to be the structural ground for cross-talk between cell-surface and intracellular ionic channels. Our current studies have identified junctophilins (JPs) as members of a novel transmembrane protein family in the junctional membrane complex. Biochemical and gene-knockout studies have suggested that JPs contribute to the formation of the junctional membrane complex by spanning the intracellular store membrane and interacting with the plasma membrane. We report here invertebrate JPs in fruit fly and nematode. Three distinct JP subtype genes are found in the mammalian genome, while a single JP gene exists in either invertebrate genome. Mammalian and invertebrate JPs share characteristic structural features, although some intervening sequences are found in invertebrate JPs. A reporter assay indicated that the JP gene is predominantly activated in muscle cells in nematode. Nematodes, in which expression of JP was inhibited by RNA-mediated interference (RNAi), showed hypolocomotion. Taking account of the cell-type-specific expression and data from previous reports, the hypolocomotion is likely to be due to the deficiency of junctional membrane structures and the resulting reduction of Ca2+ signaling during excitation-contraction coupling in muscle cells.

Combes D et al. (2003) Eur J Neurosci "Multiple ace genes encoding acetylcholinesterases of Caenorhabditis elegans have distinct tissue expression."

Combes D, Fedon Y, Arpagaus M, Toutant JP

[Eur J Neurosci, 2003]

ace-1 and ace-2 genes encoding acetylcholinesterase in the nematode Caenorhabditis elegans present 35% identity in coding sequences but no homology in noncoding regions (introns, 5'- and 3'-untranslated regions). A 5'-region of ace-2 was defined by rescue of ace-1 ;ace-2 mutants. When green fluorescent protein (GFP) expression was driven by this regulatory region, the resulting pattern was distinct from that of ace-1 . This latter gene is expressed in all body-wall and vulval muscle cells (Culetto et al ., 1999), whereas ace-2 is expressed almost exclusively in neurons. ace-3 and ace-4 genes are located in close proximity on chromosome II (Combes et al ., 2000). These two genes were first transcribed in vivo as a bicistronic messenger and thus constitute an ace-3 ;ace-4 operon. However, there was a very low level of monocistronic mRNA of ace-4 (the upstream gene) in vivo , and no ACE-4 enzymatic activity was ever detected. GFP expression driven by a 5' upstream region of the ace-3 ;ace-4 operon was detected in several muscle cells of the pharynx (pm3, pm4, pm5 and pm7) and in the two canal associated neurons (CAN cells). A dorsal row of body-wall muscle cells was intensively labelled in larval stages but no longer detected in adults. The distinct tissue-specific expression of ace-1 , ace-2 and ace-3 (coexpressed only in pm5 cells) indicates that ace

Springer W et al. (2005) Hum Mol Genet "A Caenorhabditis elegans Parkin mutant with altered solubility couples alpha-synuclein aggregation to proteotoxic stress."

Springer W, Hoppe T, Schmidt E, Baumeister R

[Hum Mol Genet, 2005]

Mutations in the human parkin gene encoding an E3 ubiquitin ligase have been associated with early-onset recessive forms of Parkinson''s disease (PD). However, the molecular mechanisms by which mutations in the parkin gene cause PD are still under debate. Here, we identified and characterized the Caenorhabditis elegans parkin homolog, pdr-1. PDR-1 protein physically associates and cooperates with a conserved degradation machinery to mediate ubiquitin conjugation. Strikingly, in contrast to pdr-1 loss-of-function mutants, an in-frame deletion variant with altered solubility and intracellular localization properties is hypersensitive towards different proteotoxic stress conditions. Both endoplasmic reticulum-derived folding stress and cytosolic stress conferred by expression of mutant human alpha-synuclein resulted in severe developmental defects and lethality in pdr-1(lg103) mutant background. Furthermore, we show that the corresponding truncated protein PDR-1(Deltaaa24-247) aggregates in cell culture, but still interacts with its ubiquitylation co-enzymes. Thus, it might block the cellular degradation/detoxification machinery and therefore renders worms highly vulnerable to protein folding stress. In contrast to other complete gene knock-outs or RNAi models of Parkin function, this C. elegans model recapitulates Parkin insolubility and aggregation similar to several AR-JP linked Parkin mutations. We suggest that such Parkin variants that either confer a neomorphic function or a partial loss-of-function may help to further elucidate the biological function of Parkin in vivo and the pathogenic mechanisms resulting in AR-JP. Due to high-throughput capacity of C. elegans, this model is particularly well suited to identify genetic and chemical modifiers of toxicity.