Voltage imaging in Drosophila using a hybrid chemical-genetic rhodamine voltage reporter

We combine a chemically-synthesized, voltage-sensitive fluorophore with a genetically encoded, self-labeling enzyme to enable voltage imaging in Drosophila melanogaster. Previously, we showed that a rhodamine voltage reporter (RhoVR) combined with the HaloTag self-labeling enzyme could be used to monitor membrane potential changes from mammalian neurons in culture and brain slice. Here, we apply this hybrid RhoVR-Halo approach in vivo to achieve selective neuron labeling in intact fly brains. We generate a Drosophila UAS-HaloTag reporter line in which the HaloTag enzyme is expressed on the surface of cells. We validate the voltage sensitivity of this new construct in cell culture before driving expression of HaloTag in specific brain neurons in flies. We show that selective labeling of synapses, cells, and brain regions can be achieved with RhoVR-Halo in either larval neuromuscular junction (NMJ) or in whole adult brains. Finally, we validate the voltage sensitivity of RhoVR-Halo in fly tissue via dual-electrode/imaging at the NMJ, show the efficacy of this approach for measuring synaptic excitatory post-synaptic potentials (EPSPs) in muscle cells, and perform voltage imaging of carbachol-evoked depolarization and osmolarity-evoked hyperpolarization in projection neurons and in interoceptive subesophageal zone neurons in fly brain explants following in vivo labeling. We envision the turn-on response to depolarizations, fast response kinetics, and two-photon compatibility of chemical indicators, coupled with the cellular and synaptic specificity of genetically-encoded enzymes, will make RhoVR-Halo a powerful complement to neurobiological imaging in Drosophila.

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Imaging Subthreshold Voltage Oscillation With Cellular Resolution in the Inferior Olive in vitro

Frontiers in Cellular Neuroscience ◽

10.3389/fncel.2020.607843 ◽

2020 ◽

Vol 14 ◽

Author(s):

Kevin Dorgans ◽

Bernd Kuhn ◽

Marylka Yoe Uusisaari

Keyword(s):

Inferior Olive ◽

Brain Slices ◽

Brain Regions ◽

Mammalian Brain ◽

Wide Field ◽

Voltage Imaging ◽

Subthreshold Oscillations ◽

Cellular Resolution

Voltage imaging with cellular resolution in mammalian brain slices is still a challenging task. Here, we describe and validate a method for delivery of the voltage-sensitive dye ANNINE-6plus (A6+) into tissue for voltage imaging that results in higher signal-to-noise ratio (SNR) than conventional bath application methods. The not fully dissolved dye was injected into the inferior olive (IO) 0, 1, or 7 days prior to acute slice preparation using stereotactic surgery. We find that the voltage imaging improves after an extended incubation period in vivo in terms of labeled volume, homogeneous neuropil labeling with saliently labeled somata, and SNR. Preparing acute slices 7 days after the dye injection, the SNR is high enough to allow single-trial recording of IO subthreshold oscillations using wide-field (network-level) as well as high-magnification (single-cell level) voltage imaging with a CMOS camera. This method is easily adaptable to other brain regions where genetically-encoded voltage sensors are prohibitively difficult to use and where an ultrafast, pure electrochromic sensor, like A6+, is required. Due to the long-lasting staining demonstrated here, the method can be combined, for example, with deep-brain imaging using implantable GRIN lenses.

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Sensitivity optimization of a rhodopsin-based fluorescent voltage indicator

10.1101/2021.11.09.467909 ◽

2021 ◽

Author(s):

Ahmed S Abdelfattah ◽

Jihong Zheng ◽

Daniel Reep ◽

Getahun Tsegaye ◽

Arthur Tsang ◽

...

Keyword(s):

Saturation Mutagenesis ◽

Voltage Sensitivity ◽

Voltage Imaging ◽

Neuronal Populations ◽

Lower Baseline ◽

Transmembrane Voltage ◽

Automated Patch Clamp ◽

Subthreshold Voltage ◽

Voltage Indicator

The ability to optically image cellular transmembrane voltage at millisecond-timescale resolution can offer unprecedented insight into the function of living brains in behaving animals. The chemigenetic voltage indicator Voltron is bright and photostable, making it a favorable choice for long in vivo imaging of neuronal populations at cellular resolution. Improving the voltage sensitivity of Voltron would allow better detection of spiking and subthreshold voltage signals. We performed site saturation mutagenesis at 40 positions in Voltron and screened for increased ΔF/F0 in response to action potentials (APs) in neurons. Using a fully automated patch-clamp system, we discovered a Voltron variant (Voltron.A122D) that increased the sensitivity to a single AP by 65% compared to Voltron. This variant (named Voltron2) also exhibited approximately 3-fold higher sensitivity in response to sub-threshold membrane potential changes. Voltron2 retained the sub-millisecond kinetics and photostability of its predecessor, with lower baseline fluorescence. Introducing the same A122D substitution to other Ace2 opsin-based voltage sensors similarly increased their sensitivity. We show that Voltron2 enables improved sensitivity voltage imaging in mice, zebrafish and fruit flies. Overall, we have discovered a generalizable mutation that significantly increases the sensitivity of Ace2 rhodopsin-based sensors, improving their voltage reporting capability.

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Long-wavelength Fluorophores for Voltage Sensing

10.26434/chemrxiv.7663124.v2 ◽

2019 ◽

Cited By ~ 1

Author(s):

Gloria Ortiz ◽

Pei Liu ◽

Su Naing ◽

Vikram Muller ◽

Evan Miller

Keyword(s):

Fluorescent Protein ◽

Voltage Sensitivity ◽

Porcine Liver ◽

Design Synthesis ◽

Fluorescent Indicators ◽

Voltage Imaging ◽

Chemical Genetic ◽

Green Fluorescent ◽

Oxygen Substitution

We present the design, synthesis, and applications of a new class of voltage-sensitive fluorescent indicators built on a modified carbofluorescein scaffold. Carbofluoresceins are an attractive target for responsive probes because they maintain oxygen substitution patterns at the 3' and 6' positions, similar to fluorescein, while simultaneously possessing excitation and emission profiles red-shifted nearly 50 nm compared to fluorescein. However, the high pKa of carbofluorescein dyes, coupled with their tendency to cyclize to non-fluorescent configurations precludes their use in voltage-imaging applications. Here, we overcome the limitations of carbofluoresceins via chlorination to lower the pKa by 2 units to 5.2 and sulfonation to prevent cyclization to the non-absorbing form. To achieve this, we devise a synthetic route to halogenated sulfonated carbofluoresceins from readily available, inexpensive starting materials. New, chlorinated sulfone carbofluoresceins have low pKa values (5.2) and can be incorporated into phenylenevinylene molecular wire scaffolds to create carboVoltage-sensitive Fluorophores (carboVF dyes). The best of the new carboVF dyes, carboVF2.1(OMe).Cl, possesses excitation and emission profiles >560 nm, displays high voltage sensitivity (>30% ΔF/F per 100 mV), and can be used in the presence of other blue-excited fluorophores like green fluorescent protein (GFP). Because carboVF2.1(OMe).Cl contains a phenolic oxygen, it can be incorporated into fluorogenic labeling strategies. Alkylation with a sterically bulky cyclopropylmethyl-derived acetoxymethyl ether renders carboVF weakly fluorescent; we show that fluorescence can be restored by the action of porcine liver esterase (PLE) both in vitro and on the surface of living cells and neurons. Together, these results suggest chlorinated sulfone carbofluoresceins can be promising candidates for hybrid chemical-genetic voltage imaging at wavelengths beyond typical fluorescein excitation and emission.

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Long-wavelength Fluorophores for Voltage Sensing

10.26434/chemrxiv.7663124.v1 ◽

2019 ◽

Author(s):

Gloria Ortiz ◽

Pei Liu ◽

Su Naing ◽

Vikram Muller ◽

Evan Miller

Keyword(s):

Fluorescent Protein ◽

Voltage Sensitivity ◽

Porcine Liver ◽

Design Synthesis ◽

Fluorescent Indicators ◽

Voltage Imaging ◽

Chemical Genetic ◽

Green Fluorescent ◽

Oxygen Substitution

We present the design, synthesis, and applications of a new class of voltage-sensitive fluorescent indicators built on a modified carbofluorescein scaffold. Carbofluoresceins are an attractive target for responsive probes because they maintain oxygen substitution patterns at the 3' and 6' positions, similar to fluorescein, while simultaneously possessing excitation and emission profiles red-shifted nearly 50 nm compared to fluorescein. However, the high pKa of carbofluorescein dyes, coupled with their tendency to cyclize to non-fluorescent configurations precludes their use in voltage-imaging applications. Here, we overcome the limitations of carbofluoresceins via chlorination to lower the pKa by 2 units to 5.2 and sulfonation to prevent cyclization to the non-absorbing form. To achieve this, we devise a synthetic route to halogenated sulfonated carbofluoresceins from readily available, inexpensive starting materials. New, chlorinated sulfone carbofluoresceins have low pKa values (5.2) and can be incorporated into phenylenevinylene molecular wire scaffolds to create carboVoltage-sensitive Fluorophores (carboVF dyes). The best of the new carboVF dyes, carboVF2.1(OMe).Cl, possesses excitation and emission profiles >560 nm, displays high voltage sensitivity (>30% ΔF/F per 100 mV), and can be used in the presence of other blue-excited fluorophores like green fluorescent protein (GFP). Because carboVF2.1(OMe).Cl contains a phenolic oxygen, it can be incorporated into fluorogenic labeling strategies. Alkylation with a sterically bulky cyclopropylmethyl-derived acetoxymethyl ether renders carboVF weakly fluorescent; we show that fluorescence can be restored by the action of porcine liver esterase (PLE) both in vitro and on the surface of living cells and neurons. Together, these results suggest chlorinated sulfone carbofluoresceins can be promising candidates for hybrid chemical-genetic voltage imaging at wavelengths beyond typical fluorescein excitation and emission.

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Long-wavelength Fluorophores for Voltage Sensing

10.26434/chemrxiv.7663124 ◽

2019 ◽

Author(s):

Gloria Ortiz ◽

Pei Liu ◽

Su Naing ◽

Vikram Muller ◽

Evan Miller

Keyword(s):

Fluorescent Protein ◽

Voltage Sensitivity ◽

Porcine Liver ◽

Design Synthesis ◽

Fluorescent Indicators ◽

Voltage Imaging ◽

Chemical Genetic ◽

Green Fluorescent ◽

Oxygen Substitution

We present the design, synthesis, and applications of a new class of voltage-sensitive fluorescent indicators built on a modified carbofluorescein scaffold. Carbofluoresceins are an attractive target for responsive probes because they maintain oxygen substitution patterns at the 3' and 6' positions, similar to fluorescein, while simultaneously possessing excitation and emission profiles red-shifted nearly 50 nm compared to fluorescein. However, the high pKa of carbofluorescein dyes, coupled with their tendency to cyclize to non-fluorescent configurations precludes their use in voltage-imaging applications. Here, we overcome the limitations of carbofluoresceins via chlorination to lower the pKa by 2 units to 5.2 and sulfonation to prevent cyclization to the non-absorbing form. To achieve this, we devise a synthetic route to halogenated sulfonated carbofluoresceins from readily available, inexpensive starting materials. New, chlorinated sulfone carbofluoresceins have low pKa values (5.2) and can be incorporated into phenylenevinylene molecular wire scaffolds to create carboVoltage-sensitive Fluorophores (carboVF dyes). The best of the new carboVF dyes, carboVF2.1(OMe).Cl, possesses excitation and emission profiles >560 nm, displays high voltage sensitivity (>30% ΔF/F per 100 mV), and can be used in the presence of other blue-excited fluorophores like green fluorescent protein (GFP). Because carboVF2.1(OMe).Cl contains a phenolic oxygen, it can be incorporated into fluorogenic labeling strategies. Alkylation with a sterically bulky cyclopropylmethyl-derived acetoxymethyl ether renders carboVF weakly fluorescent; we show that fluorescence can be restored by the action of porcine liver esterase (PLE) both in vitro and on the surface of living cells and neurons. Together, these results suggest chlorinated sulfone carbofluoresceins can be promising candidates for hybrid chemical-genetic voltage imaging at wavelengths beyond typical fluorescein excitation and emission.

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Long-range interhemispheric projection neurons show biased response properties and fine-scale local subnetworks in mouse visual cortex

10.1101/795922 ◽

2019 ◽

Author(s):

Kenta M. Hagihara ◽

Ayako W. Ishikawa ◽

Yumiko Yoshimura ◽

Yoshiaki Tagawa ◽

Kenichi Ohki

Keyword(s):

Long Range ◽

Brain Regions ◽

Projection Neurons ◽

Fine Scale ◽

Local Connectivity ◽

Cortical Projection ◽

Response Properties ◽

Brain Functions ◽

Mouse Visual Cortex

SummaryIntegration of information processed separately in distributed brain regions is essential for brain functions. This integration is enabled by long-range projection neurons, and further, concerted interactions between long-range projections and local microcircuits are crucial. It is not well known, however, how this interaction is implemented in cortical circuits. Here, to decipher this logic, using callosal projection neurons (CPNs) as a model of long-range projections, we found that CPNs exhibited distinct response properties and fine-scale local connectivity patterns. In vivo 2-photon calcium imaging revealed that CPNs showed a higher ipsilateral eye (with respect to their somata) preference, and that CPN pairs showed stronger signal/noise correlation than random pairs. Slice recordings showed CPNs were preferentially connected to CPNs, demonstrating the existence of projection target-dependent fine-scale subnetworks. Collectively, our results suggest that long-range projection target predicts response properties and local connectivity of cortical projection neurons.

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Visual projection neurons in the Drosophila lobula link feature detection to distinct behavioral programs

eLife ◽

10.7554/elife.21022 ◽

2016 ◽

Vol 5 ◽

Cited By ~ 94

Author(s):

Ming Wu ◽

Aljoscha Nern ◽

W Ryan Williamson ◽

Mai M Morimoto ◽

Michael B Reiser ◽

...

Keyword(s):

Visual Processing ◽

Feature Detection ◽

Brain Structures ◽

Brain Regions ◽

Projection Neurons ◽

Small Object ◽

Two Photon ◽

Visual Projection ◽

Anatomical Connection

Visual projection neurons (VPNs) provide an anatomical connection between early visual processing and higher brain regions. Here we characterize lobula columnar (LC) cells, a class of Drosophila VPNs that project to distinct central brain structures called optic glomeruli. We anatomically describe 22 different LC types and show that, for several types, optogenetic activation in freely moving flies evokes specific behaviors. The activation phenotypes of two LC types closely resemble natural avoidance behaviors triggered by a visual loom. In vivo two-photon calcium imaging reveals that these LC types respond to looming stimuli, while another type does not, but instead responds to the motion of a small object. Activation of LC neurons on only one side of the brain can result in attractive or aversive turning behaviors depending on the cell type. Our results indicate that LC neurons convey information on the presence and location of visual features relevant for specific behaviors.

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Faculty Opinions recommendation of Chemical genetic control of protein levels: selective in vivo targeted degradation.

Faculty Opinions – Post-Publication Peer Review of the Biomedical Literature ◽

10.3410/f.1018357.209534 ◽

2004 ◽

Author(s):

Dennis Hall

Keyword(s):

Genetic Control ◽

Chemical Genetic ◽

Protein Levels

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Growth Factor Therapy for Parkinson’s Disease: Alternative Delivery Systems

Journal of Parkinson s Disease ◽

10.3233/jpd-212662 ◽

2021 ◽

pp. 1-7

Author(s):

Sarah Jarrin ◽

Abrar Hakami ◽

Ben Newland ◽

Eilís Dowd

Keyword(s):

Parkinson’S Disease ◽

Gene Therapy ◽

Parkinson's Disease ◽

Growth Factors ◽

Growth Factor ◽

Ex Vivo ◽

Brain Regions ◽

Delivery Systems ◽

Alternative Delivery

Despite decades of research and billions in global investment, there remains no preventative or curative treatment for any neurodegenerative condition, including Parkinson’s disease (PD). Arguably, the most promising approach for neuroprotection and neurorestoration in PD is using growth factors which can promote the growth and survival of degenerating neurons. However, although neurotrophin therapy may seem like the ideal approach for neurodegenerative disease, the use of growth factors as drugs presents major challenges because of their protein structure which creates serious hurdles related to accessing the brain and specific targeting of affected brain regions. To address these challenges, several different delivery systems have been developed, and two major approaches—direct infusion of the growth factor protein into the target brain region and in vivo gene therapy—have progressed to clinical trials in patients with PD. In addition to these clinically evaluated approaches, a range of other delivery methods are in various degrees of development, each with their own unique potential. This review will give a short overview of some of these alternative delivery systems, with a focus on ex vivo gene therapy and biomaterial-aided protein and gene delivery, and will provide some perspectives on their potential for clinical development and translation.

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