The development of axons and dendrites is controlled by small GTP-binding proteins of the Rho family, but the upstream signaling mechanisms responsible for such regulation remain unclear. We have now investigated the role of the transmembrane protein cluster of differentiation 47 (CD47) in this process with hippocampal neurons. CD47-deficient neurons manifested markedly impaired development of dendrites and axons, whereas overexpression of CD47 promoted such development. Interaction of SH2 domain-containing protein tyrosine phosphatase substrate-1 (SHPS-1) with CD47 also induced the formation of dendritic filopodia and spines. These effects of CD47 were prevented by inhibition of either cell division cycle 42 (Cdc42) or Rac. In CD47-deficient neurons, autophosphorylation of Src was markedly reduced. In addition, overexpression of CD47 promoted the autophosphorylation of Src. Inhibition of Src family kinases indeed prevented CD47-promoted dendritic development. Inhibition of either FGD1-related Cdc42-guanine nucleotide exchange factor (GEF) (FRG) or Vav2, which is a GEF for Cdc42 and Rac and is activated by Src, also prevented the effects of CD47 on dendritic development. These results indicate that CD47 promotes development of dendrites and axons in hippocampal neurons in a manner dependent, at least in part, on activation of Cdc42 and Rac mediated by Src as well as by FRG and Vav2.

No abstract

A characteristic subset of microglia expressing CD11c appears in response to brain damage. However, the functional role of CD11c+ microglia, as well as the mechanism of its induction, are poorly understood. Here we report that the genetic ablation of signal regulatory protein α (SIRPα), a membrane protein, induced the emergence of CD11c+ microglia in the brain white matter. Mice lacking CD47, a physiological ligand of SIRPα, and microglia-specific SIRPα-knockout mice exhibited the same phenotype, suggesting that an interaction between microglial SIRPα and CD47 on neighbouring cells suppressed the emergence of CD11c+ microglia. A lack of SIRPα did not cause detectable damage to the white matter, but resulted in the increased expression of genes whose expression is characteristic of the repair phase after demyelination. In addition, cuprizone-induced demyelination was alleviated by the microglia-specific ablation of SIRPα. Thus, microglial SIRPα suppresses the induction of CD11c+ microglia that have the potential to accelerate the repair of damaged white matter.

Favipiravir was initially developed as an antiviral drug against influenza and is currently used in clinical trials against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection (COVID-19). This agent is presumably involved in RNA chain termination during influenza virus replication, although the molecular interactions underlying its potential impact on the coronaviruses including SARS-CoV-2, SARS-CoV, and Middle East respiratory syndrome coronavirus (MERS-CoV) remain unclear. We performed in silico studies to elucidate detailed molecular interactions between favipiravir and the SARS-CoV-2, SARS-CoV, MERS-CoV, and influenza virus RNA-dependent RNA polymerases (RdRp). As a result, no interactions between favipiravir ribofuranosyl-5′-triphosphate (F-RTP), the active form of favipiravir, and the active sites of RdRps (PB1 proteins) from influenza A (H1N1)pdm09 virus were found, yet the agent bound to the tunnel of the replication genome of PB1 protein leading to the inhibition of replicated RNA passage. In contrast, F-RTP bound to the active sites of coronavirus RdRp in the presence of the agent and RdRp. Further, the agent bound to the replicated RNA terminus in the presence of agent, magnesium ions, nucleotide triphosphate, and RdRp proteins. These results suggest that favipiravir exhibits distinct mechanisms of action against influenza virus and various coronaviruses.

28A characteristic subset of microglia expressing CD11c appears in response to brain 29 damage. However, the functional role of CD11c + microglia, as well as the mechanism of 30 its induction, are poorly understood. Here we report that the genetic ablation of signal 31 regulatory protein α (SIRPα), a membrane protein, induced CD11c + microglia in the 32 brain white matter. Mice lacking CD47, a physiological ligand of SIRPα, and 33 microglia-specific SIRPα knockout mice exhibited the same phenotype, suggesting the 34 interaction between microglial SIRPα and CD47 on neighbouring cells suppressed the 35 emergence of CD11c + microglia. A lack of SIRPα did not cause detectable damage in 36 the white matter, but resulted in the increased expression of genes characteristic of the 37 repair phase after demyelination. In addition, cuprizone-induced demyelination was 38 alleviated by the microglia-specific ablation of SIRPα. Thus, microglial SIRPα 39 suppresses the induction of CD11c + microglia that have the potential to accelerate the 40 repair of damaged white matter. 41 (Safaiyan et al., 2016). It was also shown that demyelination markedly induced CD11c + 63 microglia, even in the adult brain (Remington et al., 2007), which was suppressed in 64 mutant mice lacking Trem2 or Cx3Cr1 (Lampron et al., 2015; Poliani et al., 2015), i.e. 65 functional molecules that promote phagocytosis. Of note, the clearance of myelin debris 66 was markedly impaired in these mutant mice (Cantoni et al., 2015; Lampron et al., 67 2015; Poliani et al., 2015). CD11c + microglia also accumulate around amyloid plaques Results 94 Emergence of CD11c + microglia in the brain white matter of SIRPα-deficient mice 95To examine the role of SIRPα in microglial activation, brains of SIRPα knockout (KO) 96 mice were subjected to immunohistochemical analysis using antibodies specific to Iba1, 97 a microglia marker, and to CD68, a marker for phagocytically active microglia ( Figure 98 1A). In the brains of SIRPα KO mice, numbers of Iba1 + as well as Iba1 + /CD68 + cells 99 were significantly increased in the white matter, such as the fimbria, compared with 100 wild-type (WT) control mice, suggesting the activation of microglia in these regions 101 (Figures 1A and 1B). Activation of microglia in the white matter was similar to the 102 phenotype reported in aged mice, in which numbers of CD11c + microglia were reported 103 to be increased (Kaunzner et al., 2012). Next we examined the effect of the genetic 104 ablation of SIRPα on the expression of CD11c on microglia by using CD11c-EYFP 105 transgenic (Tg) mice (Lindquist et al., 2004), in which the expression of CD11c is 106 detected with a reporter gene. In SIRPα KO:CD11c-EYFP Tg mice, Iba1 + cells and 107 EYFP + cells were markedly increased in the white matter, including the corpus callosum, 108 external capsule, fimbria, and internal capsule, compared with control 109 SIRPα +/+ :CD11c-EYFP Tg mice (Figure 1C). Most EYFP + cells in the white matter of 110 SIRPα KO mice were Iba1 positive, suggesting th...