Myoblast fusion is tightly regulated during development and regeneration of muscle fibers. BAI3 is a receptor that orchestrates myoblast fusion via Elmo/Dock1 signaling, but the mechanisms regulating its activity remain elusive. Here we report that mice lacking BAI3 display small muscle fibers and inefficient muscle regeneration after cardiotoxin-induced injury. We describe two proteins that repress or activate BAI3 in muscle progenitors. We find that the secreted C1q-like1–4 proteins repress fusion by specifically interacting with BAI3. Using a proteomic approach, we identify Stabilin-2 as a protein that interacts with BAI3 and stimulates its fusion promoting activity. We demonstrate that Stabilin-2 activates the GPCR activity of BAI3. The resulting activated heterotrimeric G-proteins contribute to the initial recruitment of Elmo proteins to the membrane, which are then stabilized on BAI3 through a direct interaction. Collectively, our results demonstrate that the activity of BAI3 is spatiotemporally regulated by C1qL4 and Stabilin-2 during myoblast fusion.

Amyloid-b peptide (Ab), especially its oligomeric form, is believed to play an important role in the pathogenesis of Alzheimer's disease (AD) The number of Alzheimer's disease (AD) patients has been increasing continuously and the cost for patient treatment and care has developed into a serious social burden (Mangialasche et al. In addition to the neurotoxicity, the role of Ab oligomer in synaptic functional disorders in AD has been paid much attention recently (Palop and Mucke 2010). For example, long-term potentiation (LTP) is believed to be involved in memory function, and Ab oligomers have been reported to exert an inhibitory effect on LTP in mouse hippocampal slices (Walsh et al. 2002;Shankar et al. 2008). On the other hand, the role of Ab oligomer as a ligand for some endogenous receptors has also been considered in-depth recently (Dinamarca et al. 2012). A number of proteins, such as cellular prion protein (PrP C ) and ephrin receptor B2 (EphB2), were identified as such receptors (Lauren et al. 2009;Cisse et al. 2011). Among these proteins, the role of PrP C in synaptic dysfunction in AD has been elucidated extensively. PrP C is a cell surface glycoprotein that undergoes a conformational change in prion disorders (Biasini et al. 2012). An antibody against PrP C restored LTP induction in hippocampal slices in the presence of Ab oligomers (Freir et al. 2011). Intraperitoneal administration Received January 6, 2015; revised manuscript received April 16, 2015; accepted April 30, 2015. Address correspondence and reprint requests to Dr Tohru Mizushima, Department of Drug Discovery and Development, Faculty of Pharmacy, Keio University, 1-5-30, Shibakoen, Minato-ku, Tokyo 105-8512, Japan. E-mail: mizushima-th@pha.keio.ac.jp Abbreviations used: ABTS, 2,2 0 -azino-bis(3-ethylbenzothiazoline-6-sulfonic acid); aCSF, artificial cerebrospinal fluid; AD, Alzheimer's disease; APP, b-amyloid precursor protein; Ab, amyloid b peptide; BSA, bovine serum albumin; DSS, dextran sulfate sodium; EphB2, ephrin receptor B2; FBS, fetal bovine serum; fEPSP, field excitatory postsynaptic potential; HFS, high-frequency stimulation; HRP, horseradish peroxidase; LTP, long-term potentiation; mGluR5, metabotropic glutamate receptor 5; PFA, paraformaldehyde; PrP C , cellular prion protein.

Nucleophilic transformations of azido-containing carbonyl compounds are disclosed. The phosphazide formation from azides and di(tert-butyl)(4-(dimethylamino)phenyl)phosphine (Amphos) enabled transformations of carbonyl groups with nucleophiles such as lithium aluminum hydride and organometallic...

Ephrin type‐B receptor 2 (EphB2) is a member of the receptor tyrosine kinase family and plays an important role in learning and memory functions. In patients with Alzheimer's disease ( AD ) and in mouse models of AD , a reduction in the hippocampal EphB2 level is observed. It was recently reported that normalization of the EphB2 level in the dentate gyrus rescues memory function in a mouse model of AD , suggesting that drugs that restore EphB2 levels may be beneficial in the treatment of AD . Amyloid β (Aβ) oligomers, which are believed to be key molecules involved in the pathogenesis of AD , induce EphB2 degradation through their direct binding to EphB2. Thus, compounds that inhibit the binding of Aβ oligomers to EphB2 may be beneficial. Here, we screened for such compounds from drugs already approved for clinical use in humans. Utilizing a cell‐free screening assay, we determined that dihydroergotamine mesilate, bromocriptine mesilate, cepharanthine, and levonorgestrel inhibited the binding of Aβ oligomers to EphB2 but not to cellular prion protein, another endogenous receptor for Aβ oligomers. Additionally, these four compounds did not affect the binding between EphB2 and ephrinB2, an endogenous ligand for EphB2, suggesting that the compounds selectively inhibited the binding of Aβ oligomers to EphB2. This is the first identification of compounds that selectively inhibit the binding of Aβ oligomers to EphB2. These results suggest that these four compounds may be safe and effective drugs for treatment of AD .

Changes in neural activity induced by learning and novel environments have been reported to lead to the formation of new synapses in the adult brain. However, the underlying molecular mechanism is not well understood. Here, we show that Purkinje cells (PCs), which have established adult-type monosynaptic innervation by climbing fibers (CFs) after elimination of weak CFs during development, can be reinnervated by multiple CFs by increased expression of the synaptic organizer C1ql1 in CFs or Bai3, a receptor for C1ql1, in PCs. In the adult cerebellum, CFs are known to have transverse branches that run in a mediolateral direction without forming synapses with PCs. Electrophysiological, Ca2+-imaging and immunohistochemical studies showed that overexpression of C1ql1 or Bai3 caused these CF transverse branches to elongate and synapse on the distal dendrites of mature PCs. Mature PCs were also reinnervated by multiple CFs when the glutamate receptor GluD2, which is essential for the maintenance of synapses between granule cells and PCs, was deleted. Interestingly, the effect of GluD2 knockout was not observed in Bai3 knockout PCs. In addition, C1ql1 levels were significantly upregulated in CFs of GluD2 knockout mice, suggesting that endogenous, not overexpressed, C1ql1-Bai3 signaling could regulate the reinnervation of mature PCs by CFs. Furthermore, the effects of C1ql1 and Bai3 overexpression required neuronal activity in the PC and CF, respectively. C1ql1 immunoreactivity at CF-PC synapses was reduced when the neuronal activity of CFs was suppressed. These results indicate that C1ql1-Bai3 signaling mediates CF synaptogenesis in mature PCs in concert with neuronal activity.