It is well established that auxiliary proteins play a critical role in the trafficking and function of voltage-gated ion channels. However, until recently it was thought that ionotropic neurotransmitter receptors operated independently of auxiliary subunits. This view changed with the discovery of the tetraspanning membrane protein stargazin, the protein that is mutated in the ataxic mouse stargazer. Cerebellar granule neurons (CGNs), in which stargazin is highly expressed, lack surface AMPA type glutamate receptors (AMPARs) in the stargazer mouse. In addition to controlling AMPAR trafficking, stargazin also controls AMPAR gating, thus establishing it as a bona fide AMPAR auxiliary subunit. Stargazin is a member of a family of proteins termed transmembrane AMPAR regulatory proteins (TARPs), which have both distinct and overlapping properties to stargazin (Coombs and Cull-Candy, 2009; Diaz, 2010; Jackson and Nicoll, 2011; Kato et al., 2010b; Straub and Tomita, 2011). Additional AMPAR auxiliary subunits, unrelated to TARPs, have been identified from a variety of screens (Wang et al., 2008; Zheng et al., 2004). Among these proteins are cornichon-2 and -3 (CNIH-2 and CNIH-3) (Schwenk et al., 2009). In expression
