A-Kinase Anchoring Proteins (AKAPs) ensure the fidelity of second messenger signaling events by directing protein kinases and phosphatases toward their preferred substrates. AKAP150 brings protein kinase A (PKA), the calcium/calmodulin dependent phosphatase PP2B and protein kinase C (PKC) to postsynaptic membranes where they facilitate the phosphorylation dependent modulation of certain ion channels. Immunofluorescence and electrophysiological recordings were combined with behavioral analyses to assess whether removal of AKAP150 by gene targeting in mice changes the signaling environment to affect excitatory and inhibitory neuronal processes. Mislocalization of PKA in AKAP150 null hippocampal neurons alters the bidirectional modulation of postsynaptic AMPA receptors with concomitant changes in synaptic transmission and memory retention. AKAP150 null mice also exhibit deficits in motor coordination and strength that are consistent with a role for the anchoring protein in the cerebellum. Loss of AKAP150 in sympathetic cervical ganglion (SCG) neurons reduces muscarinic suppression of inhibitory M currents and provides these animals with a measure of resistance to seizures induced by the non-selective muscarinic agonist pilocarpine. These studies argue that distinct AKAP150-enzyme complexes regulate contextdependent neuronal signaling events in vivo.AMPA ͉ behavior ͉ KCNQ ͉ knockout S ophisticated systems have evolved to manage the spatial and temporal organization of signal transduction pathways. AKinase Anchoring Proteins (AKAPs) target various protein kinases and phosphatases to subcellular environments where they control the phosphorylation state of neighboring substrates (1). Movement of enzymes in and out of multiprotein complexes contributes to the temporal regulation of signaling. Hence genetic manipulation of AKAP expression impacts the specificity and magnitude of cellular regulation within the context of the whole organism. This is particularly evident in the central nervous system where the elongated and branched morphology of neurons creates many intracellular compartments where AKAPs synchronize neuronal events (2-4).AKAP79/150 is a family of three orthologs (human AKAP79, murine AKAP150, and bovine AKAP75) each initially defined on the basis of its ability to tether the type II PKA holoenzyme (4, 5). Additional binding partners were subsequently identified including PP2B and PKCs (6, 7). Thus, AKAP79/150 complexes can to respond to intracellular second messengers such as cAMP, calcium and phospholipids (7). Furthermore, the simultaneous anchoring of signal transduction and signal termination enzymes influences both forward and backward steps of a cellular event. For example, AKAP79/150 complexes can influence the phosphorylation and action of transmembrane proteins including G protein coupled receptors and adenylyl cyclases (8, 9). Loss of AKAP79/150 from heart cells contributes to the onset of angiotensin II-induced hypertension (10). Electrophysiological approaches have established a role for AKAP79...

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In vertebrate unfertilized eggs, metaphase arrest in Meiosis II is mediated by an activity known as cytostatic factor (CSF). CSF arrest is dependent upon Mos-dependent activation of the MAPK/Rsk pathway, and Rsk activates the spindle checkpoint kinase Bub1, leading to inhibition of the anaphase-promoting complex (APC), an E3 ubiquitin ligase required for the metaphase/anaphase transition. However, it is not known whether Bub1 is required for the establishment of CSF arrest or whether other pathways also contribute. Here, we show that immunodepletion of Bub1 from egg extracts blocks the ability of Mos to establish CSF arrest, and arrest can be restored by the addition of wild-type, but not kinase-dead, Bub1. The appearance of CSF arrest at Meiosis II may result from coexpression of cyclin E/Cdk2 with the MAPK/Bub1 pathway. Cyclin E/Cdk2 was able to cause metaphase arrest in egg extracts even in the absence of Mos and could also inhibit cyclin B degradation in oocytes when expressed at anaphase of Meiosis I. Once it has been established, metaphase arrest can be maintained in the absence of MAPK, Bub1, or cyclin E/Cdk2 activity. Both pathways are independent of each other, but each appears to block activation of the APC, which is required for cyclin B degradation and the metaphase/anaphase transition.

Bub1, an upstream component of the kinetochore attachment checkpoint, is activated during meiosis in Xenopus in a MAPK-dependent manner. Moreover, a single substrate of MAPK, p90(Rsk), is sufficient to activate Bub1 in vitro and in vivo. These results indicate that in vertebrate eggs, kinetochore attachment/spindle assembly checkpoint proteins, including Bub1, are downstream of p90(Rsk) and may be effectors of APC inhibition and CSF-dependent metaphase arrest by p90(Rsk).