Self-perpetuating protein aggregates transmit prion diseases in mammals and heritable traits in yeast. De novo prion formation can be induced by transient overproduction of the corresponding prion-forming protein or its prion domain. Here, we demonstrate that the yeast prion protein Sup35 interacts with various proteins of the actin cortical cytoskeleton that are involved in endocytosis. Sup35-derived aggregates, generated in the process of prion induction, are associated with the components of the endocytic/vacuolar pathway. Mutational alterations of the cortical actin cytoskeleton decrease aggregation of overproduced Sup35 and de novo prion induction and increase prion-related toxicity in yeast. Deletion of the gene coding for the actin assembly protein Sla2 is lethal in cells containing the prion isoforms of both Sup35 and Rnq1 proteins simultaneously. Our data are consistent with a model in which cytoskeletal structures provide a scaffold for generation of large aggregates, resembling mammalian aggresomes. These aggregates promote prion formation. Moreover, it appears that the actin cytoskeleton also plays a certain role in counteracting the toxicity of the overproduced potentially aggregating proteins.Prions are protein isoforms that cause transmissible neurodegenerative diseases in mammals (for review, see reference 50) and control heritable traits in fungi (for review, see references 10 to 12). Most known prions are self-perpetuating amyloid-like ordered fibrous protein aggregates which propagate the prion state by immobilizing the soluble protein molecules of the same amino acid sequence. Saccharomyces cerevisiae prion [PSI ϩ ] is an aggregate of the translation termination factor Sup35. The prion domain of Sup35 is rich in glutamine (Q) and asparagine (N) residues, resembling poly-Q proteins, such as huntingtin, which is involved in Huntington's disease (for review, see reference 53). While recent data shed light on the major steps of propagation of the preexisting [PSI ϩ ] aggregates in yeast cells (for review, see references 12 and 47), the mechanism of initial prion formation from nonprion protein remains a mystery. It has been shown that de novo formation of the [PSI ϩ ] prion is induced by transient overproduction of the Sup35 protein or its prion domain (14,19). This process is usually efficient only in cells containing other QNrich protein aggregates, such as [PIN ϩ ], a prion form of Rnq1 (20, 22). Likewise, preexisting QN-rich prions promote aggregation and aggregation-related toxicity of heterologous poly-Q proteins expressed in yeast cells (33,38). Possibly, preexisting QN-rich aggregates either provide initial nucleation centers for aggregation of other QN-rich proteins or sequester unknown antiaggregation factors.Assembly of amyloid fibers resembles the assembly of cytoskeletal structures such as actin filaments. The QN-rich domain of Sup35 was shown to interact with the actin assembly protein Sla1 in the two-hybrid assay (4). Deletion of SLA1 decreases de novo induction of [PSI ϩ ] ...

During cortical synaptic development, thalamic axons must establish synaptic connections despite the presence of the more abundant intracortical projections. How thalamocortical synapses are formed and maintained in this competitive environment is unknown. Here, we show that astrocyte-secreted protein hevin is required for normal thalamocortical synaptic connectivity in the mouse cortex. Absence of hevin results in a profound, long-lasting reduction in thalamocortical synapses accompanied by a transient increase in intracortical excitatory connections. Three-dimensional reconstructions of cortical neurons from serial section electron microscopy (ssEM) revealed that, during early postnatal development, dendritic spines often receive multiple excitatory inputs. Immuno-EM and confocal analyses revealed that majority of the spines with multiple excitatory contacts (SMECs) receive simultaneous thalamic and cortical inputs. Proportion of SMECs diminishes as the brain develops, but SMECs remain abundant in Hevin-null mice. These findings reveal that, through secretion of hevin, astrocytes control an important developmental synaptic refinement process at dendritic spines.DOI: http://dx.doi.org/10.7554/eLife.04047.001

BACKGROUND Development of treatments for obsessive-compulsive disorder (OCD) is hampered by a lack of mechanistic understanding about this prevalent neuropsychiatric condition. Although circuit changes such as elevated frontostriatal activity are linked to OCD, the underlying molecular signaling that drives OCD-related behaviors remains largely unknown. Here, we examine the significance of type 5 metabotropic glutamate receptors (mGluR5s) for behavioral and circuit abnormalities relevant to OCD. METHODS Sapap3 knockout (KO) mice treated acutely with an mGluR5 antagonist were evaluated for OCD-relevant phenotypes of self-grooming, anxiety-like behaviors, and increased striatal activity. The role of mGluR5 in the striatal circuit abnormalities of Sapap3 KO mice was further explored using two-photon calcium imaging to monitor striatal output from the direct and indirect pathways. A contribution of constitutive signaling to increased striatal mGluR5 activity in Sapap3 KO mice was investigated using pharmacologic and biochemical approaches. Finally, sufficiency of mGluR5 to drive OCD-like behavior in wild-type mice was tested by potentiating mGluR5 with a positive allosteric modulator. RESULTS Excessive mGluR5 signaling underlies OCD-like behaviors and striatal circuit abnormalities in Sapap3 KO mice. Accordingly, enhancing mGluR5 activity acutely recapitulates these behavioral phenotypes in wild-type mice. In Sapap3 KO mice, elevated mGluR5 signaling is associated with constitutively active receptors and increased and imbalanced striatal output that is acutely corrected by antagonizing striatal mGluR5. CONCLUSIONS These findings demonstrate a causal role for increased mGluR5 signaling in driving striatal output abnormalities and behaviors with relevance to OCD and show the tractability of acute mGluR5 inhibition to remedy circuit and behavioral abnormalities.