GIT2 is dispensable for normal learning and memory function due to a predominant brain GIT2 splice variant that evades GIT/PIX complexes

G protein-coupled receptor kinase-interacting protein 2 (GIT2) and GIT1 are highly similar, sharing the same domain structure and many binding partners. The most important GIT partners are the p21-activated protein kinase-interacting exchange factor (PIX) proteins, since through homomeric and heteromeric interactions, GIT and PIX proteins form oligomeric GIT/PIX complexes. Oligomeric GIT/PIX complexes function both as regulators of small GTP-binding proteins and as scaffolds for signalling molecules, including p21-activated protein kinases (PAKs). Deficits in learning and memory have been demonstrated in GIT1 knockout mice, and it has been assumed that GIT2 also would affect learning and memory. Unexpectedly, we find that GIT2-deficient mice respond normally in multiple tests of learning and memory, and have normal hippocampal long-term potentiation. Further, we find no evidence that GIT2 regulates ADHD-like phenotypes. To investigate why GIT2 and GIT1 differ so markedly in the brain, we identified the major isoform of GIT2 in the brain as a previously uncharacterized splice variant, GIT2(ΔBCE). This variant cannot dimerize or form oligomeric complexes with PIX proteins, and is thus incapable of regulating PAK in synapses, compared to oligomeric GIT1/PIX complexes. Because localized activation of PAK in synapses is required for structural plasticity underlying cognitive performance, loss of monomeric GIT2(ΔBCE) in the brain does not influence these responses.