Scans of these gels confirmed the appearance of a protein the size of Kal8 (Fig. cortices of Kal7KOmice showed a deficit in Cdk5, a kinase known to phosphorylate Kal7 and play an essential role in synaptic function. The early stages of excitatory synaptic development proceeded normally in cortical neurons prepared from Kal7KOmice, with decreased excitatory synapses apparent only after 21 d invitro. Expression of exogenous Kal7 in Kal7KOneurons rescued this deficit. Kal7 plays an essential role in synaptic structure and function, affecting a subset of cognitive processes. Keywords:dendritic spine, hippocampus, Golgi method, LTP, passive avoidance, stress, PSD, Cdk5 == Introduction == Alterations in the placement, prevalence, and structure of dendritic spines, RSV604 racemate the site of most glutamatergic, excitatory endings in the brain, play a critical role in the synaptic plasticity underlying learning and memory (Yuste and Bonhoeffer, 2001;Ehlers, 2002;Dunaevsky and Mason, 2003;Craig et al., 2006;Knott et al., 2006;Araya et al., 2007;Craig and Kang, 2007;McAllister, 2007). Spines switch in response to stimuli generating long-term potentiation (LTP) or long-term depressive disorder (Geinisman et al., 2000;Mezey et al., 2004).In vivo, learning tasks, memory tasks, electroconvulsive shock, and exposure to hormones, cocaine, or ethanol alter spine morphology and function (Robinson et al., 2001;Fukazawa et al., 2003;Norrholm et al., 2003;Li et al., 2004;Knott et al., 2006;Lisman and Raghavachari, 2006;Jelks et al., 2007;McAllister, 2007). Inherited conditions associated with mental retardation and neurologic/psychiatric abnormalities are often associated with spine abnormalities and have revealed key functions for small GTP binding proteins of the Rho family (Meredith et al., 2000;Norrholm and Ouimet, 2000;Ramakers, 2000;Hill et al., 2006;Tabuchi et al., 2007). Variations in spine size and shape affect signal transmission by AMPA and NMDA receptors localized to the postsynaptic density (PSD). The PSD is usually a complex, 1.1 GDa molecular machine, with its many components arrayed in a tightly controlled but dynamic manner; proteomic methods (Bque et al., 2006;Collins et al., 2006;Elias et al., 2006;Sheng and Hoogenraad, 2007) reveal the presence of 300 copies of PSD-95 and 1520 tetrameric NMDA and AMPA receptors in the typical cortical PSD. Kalirin-7 (Kal7) is the only Rho GDP/GTP exchange factor (RhoGEF) recognized in purified PSDs (Penzes et al., 2001;Collins et al., 2006;Sheng and Hoogenraad, 2007). Cyclin-dependent kinase 5 (Cdk5), a Ser/Thr kinase localized to RB1 the PSD and known to phosphorylate several proteins crucial to synaptic function (Morabito et al., 2004;Cheung et al., 2006;Cheung and Ip, 2007;Zhang et al., 2008), also phosphorylates Kal7, altering its effects on spine morphology (Xin et al., 2008). Kal7 is usually colocalized with PSD-95, RSV604 racemate AMPA and NMDA receptors at excitatory synapses around the dendritic spines of CA1 hippocampal pyramidal neurons and the dendritic shafts of hippocampal GABAergic interneurons (Ma et al., 2008). Expression of Kal7 increases during the time of maximal synaptogenesis in the hippocampus (Ma et al., 2003,2008).In vitrostudies point to an important role for Kal7 in synaptic function. Exogenous Kal7 caused spine formation in aspiny GABAergic interneurons, whereas decreased expression of endogenous Kal7 caused the loss of excitatory synapses (Ma et al., RSV604 racemate 2008). The interactions of Kal7 with postsynaptic density-95 (PSD-95)/Discs large (Dlg)/zona occludens-1 (ZO-1) (PDZ) domain name proteins such as AF-6 (Xie et al., 2008) and PSD-95 (Penzes et al., 2001), coupled with the actions of the Sec14p, spectrin-like, and GEF domains it shares with the larger isoforms of Kalirin (Schiller et al., 2005,2008), all contribute to its actions. Becausein vitrostudies do not usually accurately indicatein vivofunction (Varoqueaux et al., 2006;Chubykin et al., 2007;Tabuchi et al., 2007), we designed a mouse lacking the unique exon that defines Kal7. Despite the presence of 69 RhoGEFs (Rossman et al., 2005), lack of this isoform of Kalirin results in a decreased quantity of dendritic spines and excitatory synapses. In RSV604 racemate addition to morphological changes, mice lacking Kal7 and Kal7 (Fig. 1A) exhibit decreased anxiety-like behavior, deficits in hippocampal-dependent learning, and diminished long-term potentiation. The decreased levels of Cdk5 found in PSDs purified from Kal7KOmice may contribute to many of these deficits. == Physique 1. == Kal7 knock-out strategy.A, The major isoforms of Kalirin are shown; alternate splicing of three RSV604 racemate different 3-untranslated regions generates Kal7, Kal8,.