, 2006a; Wang et al., 2008). Since then, additional transmembrane proteins have been implicated in AMPAR function ( Jackson and Nicoll, 2011; Kalashnikova et al., 2010;

Schwenk et al., 2009, 2012; von Engelhardt et al., 2010). Two outstanding questions are posed by these studies. First, are there additional auxiliary SB203580 in vitro proteins that contribute to receptor function? Second, how do the auxiliary proteins contribute to synaptic transmission and behavior? In C. elegans, the GLR-1 AMPAR mediates glutamate-gated current in a subset of interneurons that control movement and the avoidance of noxious stimuli ( Hart et al., 1995; Maricq et al., 1995). Genetic and reconstitution studies have demonstrated that GLR-1 is part of a multiprotein synaptic complex required

for GLR-1-mediated currents and behavior ( Wang et al., 2008; Zheng et al., 2004). In addition to GLR-1, this complex contains SOL-1 and at least one of the TARPs, i.e., STG-1 and STG-2. SOL-1 is an evolutionarily conserved type I transmembrane protein that contains protein-protein interaction motifs called CUB-domains (complement, Urchin learn more EGF, BMP). SOL-1 was shown to regulate the rate of GLR-1 desensitization as well as its rate of recovery from desensitization ( Walker et al., 2006a, 2006b; Zheng et al., 2006). More recently, the CUB-domain-containing transmembrane proteins Neto1 and Neto2 were identified in mice. These proteins contribute to signaling mediated by NMDA (N-methyl-D-aspartate) and kainate iGluRs, respectively ( Ng et al., 2009; Zhang et al., 2009). However, C. elegans SOL-1 and the vertebrate Neto proteins and belong to two different classes of CUB domain proteins. Whereas SOL-1 contains four predicted CUB domains, Neto1 and Neto2 contain two CUB domains and a LDLa domain (low-density lipoprotein receptor

class A). This raises the question of whether multiple classes of CUB-domain proteins contribute to the function of specific iGluRs. In an earlier study (Zheng et al., 2006), we found that a secreted form of SOL-1 (s-SOL-1) that lacked the transmembrane domain was sufficient to rescue the behavioral and synaptic signaling defects of sol-1 mutants. Here, we show that coexpression of s-SOL-1 with GLR-1 and STG-1 in heterologous cells is not sufficient to reconstitute glutamate-gated current. This result led us to the hypothesis that an additional protein, which was missing in heterologous cells, is expressed in neurons and is required for s-SOL-1 function. Presumably, this protein is part of the GLR-1 receptor complex and recruits s-SOL-1 to the complex, thus contributing to receptor function. This model also suggests that the protein itself might have a modulatory role in GLR-1 function. To identify the putative interacting protein, we used an unbiased forward genetic strategy and discovered SOL-2, a CUB-domain transmembrane protein that is the homolog of the vertebrate Neto proteins, with two CUB domains and a LDLa domain.