Corticotropin releasing factor binding protein (CRF-BP) was originally recognized as CRF sequestering protein. However, its differential subcellular localization in different brain nuclei suggests that CRF-BP may have additional functions. There is evidence that CRF-BP potentiates CRF and urocortin 1 actions through CRF type 2 receptors (CRF 2 R). CRF 2 R is a G protein-coupled receptor (GPCR) that is found mainly intracellularly as most GPCRs. The access of GPCRs to the cell surface is tightly regulated by escort proteins. We hypothesized that CRF-BP binds to CRF 2 R, exerting an escort protein role. We analyzed the colocalization of CRF-BP and CRF 2 R in cultured rat mesencephalic neurons, and the localization and interaction of heterologous expressed CRF-BP and CRF 2α R in yeast, human embryonic kidney 293, and rat pheochromocytoma 12 cells. Our results showed that CRF-BP and CRF 2 R naturally colocalize in the neurites of cultured mesencephalic neurons. Heterologous expression of each protein showed that CRF-BP was localized mainly in secretory granules and CRF 2α R in the endoplasmic reticulum. In contrast, CRF-BP and CRF 2α R colocalized when both proteins are coexpressed. Here we show that CRF-BP physically interacts with the CRF 2α R but not the CRF 2β R isoform, increasing CRF 2α R on the cell surface. Thus, CRF-BP emerges as a GPCR escort protein increasing the understanding of GPCR trafficking.T he corticotropin releasing factor (CRF) system plays a key role in the response and adaptation to stressful stimuli (1, 2) and in the interaction between stress and addiction (3). The CRF system acts on the hypothalamic-pituitary-adrenal axis (4, 5) and in different brain regions (1, 6). The CRF system includes four peptides, CRF type 1 (CRF 1 R) and type 2 (CRF 2 R), G protein-coupled receptors (GPCRs) (6-8), and CRF binding protein (CRF-BP) (9). CRF-BP was described as a circulating polypeptide in pregnant women (10, 11). CRF-BP binds CRF and urocortin with high affinity (12). Different functions have been proposed for CRF-BP (13). On one hand, CRF-BP exerts an inhibitory role by sequestering CRF peptide (9, 14-16). On other hand, a facilitatory role of CRF-BP on CRF-dependent neuronal plasticity depending on CRF 2 R in the rat ventral tegmental area (VTA) has been described (17, 18). Recently, it has been shown that CRF-BP and CRF 2 R are important for ethanol binge drinking behavior (19). The anatomical evidence showing that CRF-BP has different subcellular distribution depending on the neuronal context (20) further supports several roles for CRF-BP.Three isoforms of CRF 2 R have been reported, the α isoform being the most expressed in the brain (21). CRF 2α R is localized intracellularly in neurons of the rat dorsal raphe nucleus and that exposure to acute (22) and repeated stress (23) increases its presence in the plasma membrane. CRF 2α R overexpressed in human embryonic kidney (HEK293T) cells is associated with the endoplasmic reticulum (ER) (24). Schulz et al. (25) showed that CRF 2α R is retained in...

It has long been established that neuronal growth cone navigation depends on changes in microtubule (MT) and F-actin architecture downstream of guidance cues. However, the mechanisms by which MTs and F-actin are dually coordinated remain a fundamentally unresolved question. Here, we report that the well-characterized MT polymerase, XMAP215 (also known as CKAP5), plays an important role in mediating MT-F-actin interaction within the growth cone. We demonstrate that XMAP215 regulates MT-F-actin alignment through its N-terminal TOG 1-5 domains. Additionally, we show that XMAP215 directly binds to F-actin in vitro and co-localizes with F-actin in the growth cone periphery. We also find that XMAP215 is required for regulation of growth cone morphology and response to the guidance cue, Ephrin A5. Our findings provide the first strong evidence that XMAP215 coordinates MT and F-actin interaction in vivo. We suggest a model in which XMAP215 regulates MT extension along F-actin bundles into the growth cone periphery and that these interactions may be important to control cytoskeletal dynamics downstream of guidance cues. This article has an associated First Person interview with the first author of the paper.

Adult neurogenesis occurs in the subgranular zone of the hippocampal dentate gyrus and the subventricular zone of the lateral ventricles. This process is highly regulated by intrinsic and extrinsic factors, which may control the proliferation and/or maturation of neural progenitor cells. Adult-born neurons are integrated in preexisting networks and may have functional implications for adult brain. Here we attempt to summarize relevant findings concerning the physiological role of adult neurogenesis mainly focused on the subgranular zone, and to discuss the reduced neurogenesis observed during aging and the factors that have been involved in this phenomenon. Finally, we focus on hippocampal neurogenesis in Alzheimer's disease, reviewing animal models of the disease used for the study of this process and the conclusions that have been drawn in this context.

The Wnt signaling pathway plays important roles during different stages of neuronal development, including neuronal polarization and dendritic and axonal outgrowth. However, little is known about the identity of the Frizzled receptors mediating these processes. In the present study, we investigated the role of Frizzled-5 (Fzd5) on neuronal development in cultured Sprague-Dawley rat hippocampal neurons. We found that Fzd5 is expressed early in cultured neurons on actin-rich structures localized at minor neurites and axonal growth cones. At 4 DIV, Fzd5 polarizes towards the axon, where its expression is detected mainly at the peripheral zone of axonal growth cones, with no obvious staining at dendrites; suggesting a role of Fzd5 in neuronal polarization. Overexpression of Fzd5 during the acquisition of neuronal polarity induces mislocalization of the receptor and a loss of polarized axonal markers. Fzd5 knock-down leads to loss of axonal proteins, suggesting an impaired neuronal polarity. In contrast, overexpression of Fzd5 in neurons that are already polarized did not alter polarity, but decreased the total length of axons and increased total dendrite length and arborization. Fzd5 activated JNK in HEK293 cells and the effects triggered by Fzd5 overexpression in neurons were partially prevented by inhibition of JNK, suggesting that a non-canonical Wnt signaling mechanism might be involved. Our results suggest that, Fzd5 has a role in the establishment of neuronal polarity, and in the morphogenesis of neuronal processes, in part through the activation of the non-canonical Wnt mechanism involving JNK.

The formation and maintenance of microtubules requires their polymerisation, but little is known about how this polymerisation is regulated in cells. Focussing on the essential microtubule bundles in axons of Drosophila and Xenopus neurons, we show that the plus-end scaffold Eb1, the polymerase XMAP215/Msps and the lattice-binder Tau co-operate interdependently to promote microtubule polymerisation and bundle organisation during axon development and maintenance. Eb1 and XMAP215/Msps promote each other’s localisation at polymerising microtubule plus-ends. Tau outcompetes Eb1-binding along microtubule lattices, thus preventing depletion of Eb1 tip pools. The three factors genetically interact and show shared mutant phenotypes: reductions in axon growth, comet sizes, comet numbers and comet velocities, as well as prominent deterioration of parallel microtubule bundles into disorganised curled conformations. This microtubule curling is caused by Eb1 plus-end depletion which impairs spectraplakin-mediated guidance of extending microtubules into parallel bundles. Our demonstration that Eb1, XMAP215/Msps and Tau co-operate during the regulation of microtubule polymerisation and bundle organisation, offers new conceptual explanations for developmental and degenerative axon pathologies.