A A c ci ir rc cu ui it t s su up pp po or rt ti in ng g c co on nc ce en nt tr ra at ti io on n--i in nv va ar ri ia an nt t o od do or r p pe er rc ce ep pt ti io on n i in n D Dr ro os so op ph hi il la a A Ab bs st tr ra ac ct t B Ba ac ck kg gr ro ou un nd d: : Most odors are perceived to have the same quality over a large concentration range, but the neural mechanisms that permit concentration-invariant olfactory perception are unknown. In larvae of the vinegar fly Drosophila melanogaster, odors are sensed by an array of 25 odorant receptors expressed in 21 olfactory sensory neurons (OSNs). We investigated how subsets of larval OSNs with overlapping but distinct response properties cooperate to mediate perception of a given odorant across a range of concentrations. R Re es su ul lt ts s: : Using calcium imaging, we found that ethyl butyrate, an ester perceived by humans as fruity, activated three OSNs with response thresholds that varied across three orders of magnitude. Whereas wild-type larvae were strongly attracted by this odor across a 500-fold range of concentration, individuals with only a single functional OSN showed attraction across a narrower concentration range corresponding to the sensitivity of each ethyl butyrate-tuned OSN. To clarify how the information carried by different OSNs is integrated by the olfactory system, we characterized the response properties of local inhibitory interneurons and projection neurons in the antennal lobe. Local interneurons only responded to high ethyl butyrate concentrations upon summed activation of at least two OSNs. Projection neurons showed a reduced response to odors when summed input from two OSNs impinged on the circuit compared to when there was only a single functional OSN.C Co on nc cl lu us si io on ns s: : Our results show that increasing odor concentrations induce progressive activation of concentration-tuned olfactory sensory neurons and concomitant recruitment of inhibitory local interneurons. We propose that the interplay of combinatorial OSN input and local interneuron activation allows animals to remain sensitive to odors across a large range of stimulus intensities. B Ba ac ck kg gr ro ou un nd dSensory information varies in two major dimensions -quality and quantity. For our perception of the external world to be stable and useful, the brain must construct a relatively consistent percept of quality independent of quantity. At extremes of input quantity, concentration-invariance of stimulus quality fails. In vision, colors lose their salience at low luminance, while very high luminance can blind the visual system. In olfaction, faint odors just above the sensory threshold often lack any semantically accessible quality, while high odor concentrations can take on an irritating quality [1]. Aside from these extremes of input quantity, sensory systems retain a remarkably stable percept of quality across a large range of sensory input quantity [2].Concentration-invariant quality perception is a general feature of olfactory systems [3][4][5]. Imagi...

Herpesviruses are large double-stranded DNA viruses that replicate in the nuclei of infected cells. Spatial control of viral replication and assembly in the host nucleus is achieved by the establishment of nuclear compartments that serve to concentrate viral and host factors. How these compartments are established and maintained remains poorly understood. Pseudorabies virus (PRV) is an alpha-herpesvirus often used to study herpesvirus invasion and spread in the nervous system. Here, we report that PRV and herpes simplex virus type 1 infection of neurons results in formation of actin filaments in the nucleus. Filamentous actin is not found in the nucleus of uninfected cells. Nuclear actin filaments appear physically associated with the viral capsids, as shown by serial block-face scanning electron micropscopy and confocal microscopy. Using a green fluorescent protein-tagged viral capsid protein (VP26), we show that nuclear actin filaments form prior to capsid assembly and are required for the efficient formation of viral capsid assembly sites. We find that actin polymerization dynamics (e.g., treadmilling) are not necessary for the formation of these sites. Green fluorescent protein-VP26 foci co-localize with the actin motor myosin V, suggesting that viral capsids travel along nuclear actin filaments using myosin-based directed transport. Viral transcription, but not viral DNA replication, is required for actin filament formation. The finding that infection, by either PRV or herpes simplex virus type 1, results in formation of nuclear actin filaments in neurons, and that PRV infection of an epithelial cell line results in a similar phenotype is evidence that F-actin plays a conserved role in herpesvirus assembly. Our results suggest a mechanism by which assembly domains are organized within infected cells and provide insight into how the viral infectious cycle and host actin cytoskeleton are integrated to promote the infection process.

dRabies virus (RABV) causes a fatal zoonotic encephalitis. Disease symptoms require replication and spread of the virus within neuronal cells; however, in infected animals as well as in cell culture the virus replicates in a broad range of cell types. Here we use a single-cycle RABV and a recombinant vesicular stomatitis virus (rVSV) in which the glycoprotein (G) was replaced with that of RABV (rVSV RABV G) to examine RABV uptake into the African green monkey kidney cell line BS-C-1. Combining biochemical studies and real-time spinning-disk confocal fluorescence microscopy, we show that the predominant entry pathway of RABV particles into BS-C-1 cells is clathrin dependent. Viral particles enter cells in pits with elongated structures and incomplete clathrin coats which depend upon actin to complete the internalization process. By measuring the time of internalization and the abundance of the clathrin adaptor protein AP2, we further show that the pits that internalize RABV particles are similar to those that internalize VSV particles. Pharmacological perturbations of dynamin or of actin polymerization inhibit productive infection, linking our observations on particle uptake with viral infectivity. This work extends to RABV particles the finding that clathrin-mediated endocytosis of rhabdoviruses proceeds through incompletely coated pits which depend upon actin. R abies virus (RABV) is the prototypical member of the zoonotic lyssavirus genus responsible for fatal encephalitis in animals and humans. A single-stranded negative-sense RNA virus, RABV encases its RNA genome in a bullet-shaped, enveloped particle that incorporates a single surface glycoprotein (G). RABV G mediates all internalization steps from cell binding to membrane fusion. In addition, G is a major determinant of RABV neurotropism (1). Conjugation or pseudotyping with the ectodomain of pathogenic RABV G or peptides derived from receptor-binding regions allows retargeting of biologically active molecules to the central nervous system (CNS) for drug delivery or as neurotracers (2, 3). Since a large part of RABV pathogenesis is reliant on the virus garnering access to neurons and the CNS, G is also a determining factor in RABV virulence. The pathogenicity of attenuated strains can be effectively increased by replacing the glycoprotein with one from a neurotropic, virulent strain (4).Like other rhabdoviruses, RABV gains access to the cellular interior by endocytosis and subsequent low pH-dependent fusion (5-7). Electron micrographs of viral particles in vesicles with electron-dense coats suggest that clathrin-coated pits mediate the uptake of RABV in both neuronal and nonneuronal cells (8, 9). However, static images cannot inform on the fate of such particles or the relevance of these interactions for subsequent infection. High-resolution live-imaging techniques permit tracking of viral uptake into coated pits (10-15). Fluorescence tagging of coatedpit components and quantitative analysis methods have revealed differences for the pits engaging fluoresc...

Parkinson's disease (PD) is a complex and highly variable neurodegenerative disease. Familial PD is caused by mutations in several genes with diverse and mostly unknown functions. It is unclear how dysregulation of these genes results in the relatively selective death of nigral dopaminergic neurons (DNs). To address this question, we modeled PD by knocking out the PD genes PARKIN (PRKN), DJ-1 (PARK7), and ATP13A2 (PARK9) in independent isogenic human pluripotent stem cell (hPSC) lines. We found increased levels of oxidative stress in all PD lines. Increased death of DNs upon differentiation was found only in the PARKIN knockout line. Using quantitative proteomics, we observed dysregulation of mitochondrial and lysosomal function in all of the lines, as well as common and distinct molecular defects caused by the different PD genes. Our results suggest that precise delineation of PD subtypes will require evaluation of molecular and clinical data.