Molecular, Genetic and Physiological Characterisation of Dystrobrevin-like (dyb-1) Mutants of Caenorhabditis elegans Kathrin Gieseler 1 , Marie-Christine Mariol 1 , Catherine Bessou 1 Martine Migaud 1 , Christopher J. Franks 2 , Lindy Holden-Dye 2 and Laurent Se  galat 1 * 1 CGMC, CNRS-UMR 5534 Universite  Lyon1, 43 bld du 11 Novembre, 69622 Villeurbanne cedex, France 2 School of Biological Sciences University of Southampton Bassett Crescent East Southampton, SO16 7PX, UK Dystrobrevins are protein components of the dystrophin complex, whose disruption leads to Duchenne muscular dystrophy and related diseases. The Caenorhabditis elegans dystrobrevin gene (dyb-1) encodes a protein 38 % identical with its mammalian counterparts. The C. elegans dystrobre- vin is expressed in muscles and neurons. We characterised C. elegans dyb-1 mutants and showed that: (1) their behavioural phenotype resembles that of dystrophin (dys-1) mutants; (2) the phenotype of dyb-1 dys-1 double mutants is not different from the single ones; (3) dyb-1 mutants are more sensitive than wild-type animals to reductions of acetylcholinesterase levels and have an increased response to acetyl- choline; (4) dyb-1 mutations alone do not lead to muscle degeneration, but synergistically produce a progressive myopathy when combined with a mild MyoD/hlh-1 mutation. All together, these ®ndings further sub- stantiate the role of dystrobrevins in cholinergic transmission and as functional partners of dystrophin. # 2001 Academic Press Keywords: dystrobrevin; dystrophin; Duchenne muscular dystrophy; nematode *Corresponding author Introduction Dystrophin is the protein that is absent or mutated in Duchenne and Becker muscular dystro- phies (DMD and BMD). DMD and BMD are pro- gressive diseases consisting of skeletal and cardiac myopathies, combined with electroretinopathy (Ahn & Kunkel, 1993). Dystrophin has two related proteins in mammals, utrophin (Love et al., 1989) and DRP2 (Roberts et al., 1996). Neither the func- tion of dystrophin nor that of the related proteins utrophin and DRP2 is clearly known (Michalak & Opas, 1997). Dystrophin is associated with several proteins to form the transmembrane dystrophin glycoprotein complex (DGC), which spans the muscle sarcolemma. The full-length dystrophin cDNA encodes a 427 kDa protein divided into four structural domains; an N-terminal actin-binding domain, a large central rod region consisting of spectrin-like repeats, a cysteine-rich region (CR) and a C-terminal domain comprising numerous motifs (WW domain, EF hands, ZZ domain, and two leucine heptad repeats) (Koenig et al., 1987). Utrophin and DRP2 share the same structural fea- tures (Tinsley et al., 1992; Roberts et al., 1996). The analysis of dystrophin function has been compli- cated by the overlapping expression pattern of these closely related molecules, as well as by the presence of multiple transcripts generated by the dystrophin gene (Ahn & Kunkel, 1993; Michalak & Opas, 1997). In addition, the study of dystrophin function is hindered by the relative mildness of the mouse model of DMD (mdx). Dystrobrevins form a family of proteins that are members of the DGC (Michalak & Opas, 1997; Sanes et al., 1998). Dystrophin and a-dystrobrevin co-localise at the sarcolemma (Metzinger et al., 1997). Dystrobrevins are unique in being both homologous to dystrophin and a dystrophin- associated protein. In mammals, dystrobrevins are encoded by two genes giving rise to multiple splice E-mail address of the corresponding author: segalat@maccgmc.univ-lyon1.fr Abbreviations used: DMD, Duchenne muscular dystrophy; BMD, Becker muscular dystrophy; DGC, dystrophin glycoprotein complex; gfp, green ¯uorescent protein. doi:10.1006/jmbi.2001.4480 available online at http://www.idealibrary.com on J. Mol. Biol. (2001) 307, 107±117 0022-2836/01/010107±11 $35.00/0 # 2001 Academic Press