Transsynaptic labeling and transcriptional control of zebrafish neural circuits.

Deciphering the connectome, the ensemble of synaptic connections that underlie brain function, is a central goal of neuroscience research. Here we report the in vivo mapping of connections between presynaptic and postsynaptic partners in zebrafish, by adapting the trans-Tango genetic approach that was first developed for anterograde transsynaptic tracing in Drosophila. Neural connections were visualized between synaptic partners in larval retina, brain and spinal cord and followed over development.

Convergent olfactory circuits for courtship in revealed by -Tango.

Animals exhibit sex-specific behaviors that are governed by sexually dimorphic circuits. One such behavior in male , courtship, is regulated by various sensory modalities, including olfaction. Here, we reveal how sexually dimorphic olfactory pathways in male flies converge at the third-order, onto lateral horn output neurons, to regulate courtship.

Opposing, spatially-determined epigenetic forces impose restrictions on stochastic olfactory receptor choice.

Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in the mouse genome in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development.

-Tango enables versatile retrograde circuit tracing in .

Transsynaptic tracing methods are crucial tools in studying neural circuits. Although a couple of anterograde tracing methods and a targeted retrograde tool have been developed in , there is still need for an unbiased, user-friendly, and flexible retrograde tracing system. Here, we describe -Tango, a method for transsynaptic, retrograde circuit tracing and manipulation in .

Transsynaptic labeling and transcriptional control of zebrafish neural circuits.

Deciphering the connectome, the ensemble of synaptic connections that underlie brain function is a central goal of neuroscience research. The trans-Tango genetic approach, initially developed for anterograde transsynaptic tracing in Drosophila, can be used to map connections between presynaptic and postsynaptic partners and to drive gene expression in target neurons. Here, we describe the successful adaptation of trans-Tango to visualize neural connections in a living vertebrate nervous system, that of the zebrafish.

Opposing, spatially-determined epigenetic forces impose restrictions on stochastic olfactory receptor choice.

Olfactory receptor (OR) choice represents an example of genetically hardwired stochasticity, where every olfactory neuron expresses one out of ~2000 OR alleles in a probabilistic, yet stereotypic fashion. Here, we propose that topographic restrictions in OR expression are established in neuronal progenitors by two opposing forces: polygenic transcription and genomic silencing, both of which are influenced by dorsoventral gradients of transcription factors NFIA, B, and X. Polygenic transcription of OR genes may define spatially constrained OR repertoires, among which one OR allele is selected for singular expression later in development.

Circuit analysis reveals a neural pathway for light avoidance in Drosophila larvae.

Understanding how neural circuits underlie behaviour is challenging even in the connectome era because it requires a combination of anatomical and functional analyses. This is exemplified in the circuit underlying the light avoidance behaviour displayed by Drosophila melanogaster larvae. While this behaviour is robust and the nervous system relatively simple, the circuit is only partially delineated with some contradictions among studies.

Complex representation of taste quality by second-order gustatory neurons in Drosophila.

Sweet and bitter compounds excite different sensory cells and drive opposing behaviors. However, it remains unclear how sweet and bitter tastes are represented by the neural circuits linking sensation to behavior. To investigate this question in Drosophila, we devised trans-Tango(activity), a strategy for calcium imaging of second-order gustatory projection neurons based on trans-Tango, a genetic transsynaptic tracing technique.

Coordination of two enhancers drives expression of olfactory trace amine-associated receptors.

Olfactory sensory neurons (OSNs) are functionally defined by their expression of a unique odorant receptor (OR). Mechanisms underlying singular OR expression are well studied, and involve a massive cross-chromosomal enhancer interaction network. Trace amine-associated receptors (TAARs) form a distinct family of olfactory receptors, and here we find that mechanisms regulating Taar gene choice display many unique features.

Transsynaptic mapping of mushroom body output neurons.

The mushroom body (MB) is a well-characterized associative memory structure within the brain. Analyzing MB connectivity using multiple approaches is critical for understanding the functional implications of this structure. Using the genetic anterograde transsynaptic tracing tool, Tango, we identified divergent projections across the brain and convergent downstream targets of the MB output neurons (MBONs).

Circuits that encode and guide alcohol-associated preference.

A powerful feature of adaptive memory is its inherent flexibility. Alcohol and other addictive substances can remold neural circuits important for memory to reduce this flexibility. However, the mechanism through which pertinent circuits are selected and shaped remains unclear.

Transsynaptic Mapping of Second-Order Taste Neurons in Flies by trans-Tango.

Mapping neural circuits across defined synapses is essential for understanding brain function. Here we describe trans-Tango, a technique for anterograde transsynaptic circuit tracing and manipulation. At the core of trans-Tango is a synthetic signaling pathway that is introduced into all neurons in the animal.

Identifying functional connections of the inner photoreceptors in Drosophila using Tango-Trace.

In Drosophila, the four inner photoreceptor neurons exhibit overlapping but distinct spectral sensitivities and mediate behaviors that reflect spectral preference. We developed a genetic strategy, Tango-Trace, that has permitted the identification of the connections of the four chromatic photoreceptors. Each of the four stochastically distributed chromatic photoreceptor subtypes make distinct connections in the medulla with four different TmY cells.

A critical period defined by axon-targeting mechanisms in the murine olfactory bulb.

The olfactory system remains plastic throughout life because of continuous neurogenesis of sensory neurons in the nose and inhibitory interneurons in the olfactory bulb. Here, we reveal that transgenic expression of an odorant receptor has non-cell autonomous effects on axons expressing this receptor from the endogenous gene. Perinatal expression of transgenic odorant receptor causes rerouting of like axons to new glomeruli, whereas expression after the sensory map is established does not lead to rerouting.

Alteration of genic 5-hydroxymethylcytosine patterning in olfactory neurons correlates with changes in gene expression and cell identity.

The modified DNA base 5-hydroxymethylcytosine (5hmC) is enriched in neurons where it may contribute to gene regulation and cellular identity. To determine how 5hmC influences gene expression in an in vivo neuronal population, we assessed the patterning and function of the base along the developmental lineage of the main olfactory epithelium-from multipotent stem cells through neuronal progenitors to mature olfactory sensory neurons (mOSNs). We find that 5hmC increases over gene bodies during mOSN development with substantial patterning occuring between the progenitor and mOSN stages.

An epigenetic trap stabilizes singular olfactory receptor expression.

The molecular mechanisms regulating olfactory receptor (OR) expression in the mammalian nose are not yet understood. Here, we identify the transient expression of histone demethylase LSD1 and the OR-dependent expression of adenylyl cyclase 3 (Adcy3) as requirements for initiation and stabilization of OR expression. As a transcriptional coactivator, LSD1 is necessary for desilencing and initiating OR transcription, but as a transcriptional corepressor, it is incompatible with maintenance of OR expression, and its downregulation is imperative for stable OR choice.

Nuclear aggregation of olfactory receptor genes governs their monogenic expression.

Gene positioning and regulation of nuclear architecture are thought to influence gene expression. Here, we show that, in mouse olfactory neurons, silent olfactory receptor (OR) genes from different chromosomes converge in a small number of heterochromatic foci. These foci are OR exclusive and form in a cell-type-specific and differentiation-dependent manner.

Aβ alters the connectivity of olfactory neurons in the absence of amyloid plaques in vivo.

The amyloid beta peptide aggregates into amyloid plaques at presymptomatic stages of Alzheimer's disease, but the temporal relationship between plaque formation and neuronal dysfunction is poorly understood. Here we demonstrate that the connectivity of the peripheral olfactory neural circuit is perturbed in mice overexpressing human APPsw (Swedish mutation) before the onset of plaques. Expression of human APPsw exclusively in olfactory sensory neurons also perturbs connectivity with associated reductions in odour-evoked gene expression and olfactory acuity.

Neurons expressing trace amine-associated receptors project to discrete glomeruli and constitute an olfactory subsystem.

Some chemoreceptors of the trace amine-associated receptor (TAAR) family detect innately aversive odors and are proposed to activate hardwired olfactory circuits. However, the wiring of TAAR neurons, the regulatory mechanisms of Taar gene choice, and the subcellular localization of TAAR proteins remain unknown. Here, we reveal similarities between neurons expressing TAARs and odorant receptors (ORs), but also unexpected differences.

Visualizing neuromodulation in vivo: TANGO-mapping of dopamine signaling reveals appetite control of sugar sensing.

Behavior cannot be predicted from a "connectome" because the brain contains a chemical "map" of neuromodulation superimposed upon its synaptic connectivity map. Neuromodulation changes how neural circuits process information in different states, such as hunger or arousal. Here we describe a genetically based method to map, in an unbiased and brain-wide manner, sites of neuromodulation under different conditions in the Drosophila brain.

An epigenetic signature for monoallelic olfactory receptor expression.

Constitutive heterochromatin is traditionally viewed as the static form of heterochromatin that silences pericentromeric and telomeric repeats in a cell cycle- and differentiation-independent manner. Here, we show that, in the mouse olfactory epithelium, olfactory receptor (OR) genes are marked in a highly dynamic fashion with the molecular hallmarks of constitutive heterochromatin, H3K9me3 and H4K20me3. The cell type and developmentally dependent deposition of these marks along the OR clusters are, most likely, reversed during the process of OR choice to allow for monogenic and monoallelic OR expression.

Analysis of dose to patient, spouse/caretaker, and staff, from an implanted trackable radioactive fiducial for use in the radiation treatment of prostate cancer.

Purpose: A fiducial tracking system based on a novel radioactive tracking technology is being developed for real-time target tracking in radiation therapy. In this study, the authors calculate the radiation dose to the patient, the spouse/caretaker, and the medical staff that would result from a 100 microCi Ir192 radioactive fiducial marker permanently implanted in the prostate of a radiation therapy patient.

Methods: Local tissue dose was calculated by Monte Carlo simulation.

The genetic design of signaling cascades to record receptor activation.

We have developed an experimental strategy to monitor protein interactions in a cell with a high degree of selectivity and sensitivity. A transcription factor is tethered to a membrane-bound receptor with a linker that contains a cleavage site for a specific protease. Activation of the receptor recruits a signaling protein fused to the protease that then cleaves and releases the transcription factor to activate reporter genes in the nucleus.

Interchromosomal interactions and olfactory receptor choice.

The expression of a single odorant receptor (OR) gene from a large gene family in individual sensory neurons is an essential feature of the organization and function of the olfactory system. We have used chromosome conformation capture to demonstrate the specific association of an enhancer element, H, on chromosome 14 with multiple OR gene promoters on different chromosomes. DNA and RNA fluorescence in situ hybridization (FISH) experiments allow us to visualize the colocalization of the H enhancer with the single OR allele that is transcribed in a sensory neuron.