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Optogenetics has been harnessed to shed new mechanistic light on current and future therapeutic strategies. This has been to date achieved by the regulation of ion flow and electrical signals in neuronal cells and neural circuits that are known to be affected by disease. In contrast, the optogenetic delivery of trophic biochemical signals, which support cell survival and are implicated in degenerative disorders, has never been demonstrated in an animal model of disease. Here, we reengineered the human and Drosophila melanogaster REarranged during Transfection (hRET and dRET) receptors to be activated by light, creating one-component optogenetic tools termed Opto-hRET and Opto-dRET. Upon blue light stimulation, these receptors robustly induced the MAPK/ERK proliferative signaling pathway in cultured cells. In PINK1B9 flies that exhibit loss of PTEN-induced putative kinase 1 (PINK1), a kinase associated with familial Parkinson’s disease (PD), light activation of Opto-dRET suppressed mitochondrial defects, tissue degeneration and behavioral deficits. In human cells with PINK1 loss-of-function, mitochondrial fragmentation was rescued using Opto-dRET via the PI3K/NF-кB pathway. Our results demonstrate that a light-activated receptor can ameliorate disease hallmarks in a genetic model of PD. The optogenetic delivery of trophic signals is cell type-specific and reversible and thus has the potential to inspire novel strategies towards a spatio-temporal regulation of tissue repair., Author summary The death of physiologically important cells and tissues underlies of a wide range of diseases, including the neurodegenerative disorder Parkinson’s disease. Currently, the two major strategies to counter cell degeneration are the injection of soluble growth factor peptides and growth factor gene therapy. Importantly, both strategies can lead to the undesired activation of healthy bystander cells or the non-natural permanent modification of cells and their internal signals. Here, we developed a light-based method to overcome these limitations. The use of optogenetics allowed delivering cell type-specific pro-survival signals in a genetic model of Parkinson’s disease. In Drosophila and human cells that exhibit loss of the PINK1 gene, akin to autosomal recessive Parkinson’s disease, we efficiently suppressed disease phenotypes using a light-activated tyrosine kinase receptor. This work demonstrates a ‘remote controlled’ and thus spatio-temporally precise strategy to interfere with degeneration and may open new avenues towards tissue repair in a variety of disease models, including but not limited to diseases of the brain.

Optogenetics has been harnessed to shed new mechanistic light on current therapies and to develop future treatment strategies. This has been to date achieved by the correction of electrical signals in neuronal cells and neural circuits that are affected by disease. In contrast, the optogenetic delivery of trophic biochemical signals, which support cell survival and thereby may modify progression of degenerative disorders, has never been demonstrated in an animal disease model. Here, we reengineered the human andDrosophila melanogasterREarranged during Transfection (hRET and dRET) receptors to be activated by light, creating one-component optogenetic tools termed Opto-hRET and Opto-dRET. Upon blue light stimulation, these receptors robustly induced the MAPK/ERK proliferative signaling pathway in cultured cells. In PINK1B9flies that exhibit loss of PTEN-induced putative kinase 1 (PINK1), a kinase associated with familial Parkinson’s disease (PD), light activation of Opto-dRET suppressed mitochondrial defects, tissue degeneration and behavioral deficits. In human cells with PINK1 loss-of-function, mitochondrial fragmentation was rescued using Opto-dRETviathe PI3K/NF-кB pathway. Our results demonstrate that a light-activated receptor can ameliorate disease hallmarks in a genetic model of PD. The optogenetic delivery of trophic signals is cell type-specific and reversible and thus has the potential to overcome limitations of current strategies towards a spatio-temporal regulation of tissue repair.Significance StatementThe death of physiologically important cell populations underlies of a wide range of degenerative disorders, including Parkinson’s disease (PD). Two major strategies to counter cell degeneration, soluble growth factor injection and growth factor gene therapy, can lead to the undesired activation of bystander cells and non-natural permanent signaling responses. Here, we employed optogenetics to deliver cell type-specific pro-survival signals in a genetic model of PD. InDrosophilaand human cells exhibiting loss of the PINK1 kinase, akin to autosomal recessive PD, we efficiently suppressed disease phenotypes using a light-activated tyrosine kinase receptor. This work demonstrates a spatio-temporally precise strategy to interfere with degeneration and may open new avenues towards tissue repair in disease models.

Nociception is an evolutionarily conserved mechanism to encode and process harmful environmental stimuli. Like most animals, Drosophila melanogaster larvae respond to a variety of nociceptive stimuli, including noxious touch and temperature, with stereotyped escape responses through activation of multimodal nociceptors. How behavioral responses to these different modalities are processed and integrated by the downstream network remains poorly understood. By combining trans-synaptic labeling, ultrastructural analysis, calcium imaging, optogenetics and behavioral analyses, we uncovered a circuit specific for mechanonociception but not thermonociception. Notably, integration of mechanosensory input from innocuous and nociceptive sensory neurons is required for robust mechanonociceptive responses. We further show that neurons integrating mechanosensory input facilitate primary nociceptive output by releasing short neuropeptide F, the Drosophila neuropeptide Y homolog. Our findings unveil how integration of somatosensory input and neuropeptide-mediated modulation can produce robust modality-specific escape behavior.

Dendritic arborization is highly regulated and requires tight control of dendritic growth, branching, cytoskeletal dynamics, and ion channel expression to ensure proper function. Abnormal dendritic development can result in altered network connectivity, which has been linked to neurodevelopmental disorders, including autism spectrum disorders (ASDs). How neuronal growth control programs tune dendritic arborization to ensure function is still not fully understood. UsingDrosophiladendritic arborization (da) neurons as a model, we identified the conserved Ste20-like kinase Tao as a negative regulator of dendritic arborization. We show that Tao kinase activity regulates cytoskeletal dynamics and sensory channel localization required for proper sensory function in both male and female flies. We further provide evidence for functional conservation of Tao kinase, showing that its ASD-linked human ortholog, Tao kinase 2 (Taok2), could replaceDrosophilaTao and rescue dendritic branching, dynamic microtubule alterations, and behavioral defects. However, several ASD-linked Taok2 variants displayed impaired rescue activity, suggesting that Tao/Taok2 mutations can disrupt sensory neuron development and function. Consistently, we show that Tao kinase activity is required in developing and as well as adult stages for maintaining normal dendritic arborization and sensory function to regulate escape and social behavior. Our data suggest an important role for Tao kinase signaling in cytoskeletal organization to maintain proper dendritic arborization and sensory function, providing a strong link between developmental sensory aberrations and behavioral abnormalities relevant for Taok2-dependent ASDs.SIGNIFICANCE STATEMENTAutism spectrum disorders (ASDs) are linked to abnormal dendritic arbors. However, the mechanisms of how dendritic arbors develop to promote functional and proper behavior are unclear. We identifiedDrosophilaTao kinase, the ortholog of the ASD risk gene Taok2, as a regulator of dendritic arborization in sensory neurons. We show that Tao kinase regulates cytoskeletal dynamics, controls sensory ion channel localization, and is required to maintain somatosensory functionin vivo. Interestingly, ASD-linked human Taok2 mutations rendered it nonfunctional, whereas its WT form could restore neuronal morphology and function inDrosophilalacking endogenous Tao. Our findings provide evidence for a conserved role of Tao kinase in dendritic development and function of sensory neurons, suggesting that aberrant sensory function might be a common feature of ASDs.

Sensory circuits are typically established during early development, yet how circuit specificity and function are maintained during organismal growth has not been elucidated. To gain insight we quantitatively investigated synaptic growth and connectivity in the Drosophila nociceptive network during larval development. We show that connectivity between primary nociceptors and their downstream neurons scales with animal size. We further identified the conserved Ste20-like kinase Tao as a negative regulator of synaptic growth required for maintenance of circuit specificity and connectivity. Loss of Tao kinase resulted in exuberant postsynaptic specializations and aberrant connectivity during larval growth. Using functional imaging and behavioral analysis we show that loss of Tao-induced ectopic synapses with inappropriate partner neurons are functional and alter behavioral responses in a connection-specific manner. Our data show that fine-tuning of synaptic growth by Tao kinase is required for maintaining specificity and behavioral output of the neuronal network during animal growth., It is unclear how circuit specificity and function are maintained during organismal growth. In this study, authors show that connectivity between primary nociceptors and their downstream neurons scales with animal size and that Ste20-like kinase Tao acts as a negative regulator of synaptic growth required for maintenance of circuit specificity and connectivity.

Multiple sclerosis (MS) is characterized by inflammatory insults that drive neuroaxonal injury. However, knowledge about neuron-intrinsic responses to inflammation is limited. By leveraging neuron-specific messenger RNA profiling, we found that neuroinflammation leads to induction and toxic accumulation of the synaptic protein bassoon (Bsn) in the neuronal somata of mice and patients with MS. Neuronal overexpression of Bsn in flies resulted in reduction of lifespan, while genetic disruption of Bsn protected mice from inflammation-induced neuroaxonal injury. Notably, pharmacological proteasome activation boosted the clearance of accumulated Bsn and enhanced neuronal survival. Our study demonstrates that neuroinflammation initiates toxic protein accumulation in neuronal somata and advocates proteasome activation as a potential remedy.

Thermo-nociception, the detection and behavioral response to noxious temperatures, is a highly conserved action to avoid injury and ensure survival. Basic molecular mechanisms of thermal responses have been elucidated in several model organisms and are of clinical relevance as thermal hypersensitivity (thermos-allodynia) is common in neuropathic pain syndromes. Drosophila larvae show stereotyped escape behavior upon noxious heat stimulation, which can be easily quantified and coupled with molecular genetic approaches. It has been successfully used to elucidate key molecular components and circuits involved in thermo-nociceptive responses. We provide a detailed and updated protocol of this previously described method ( Tracey et al., 2003 ) to apply a defined local heat stimulus to larvae using a fast-regulating hot probe.

Mapping brain function to brain structure is a fundamental task for neuroscience. For such an endeavour, the Drosophila larva is simple enough to be tractable, yet complex enough to be interesting. It features about 10,000 neurons and is capable of various taxes, kineses and Pavlovian conditioning. All its neurons are currently being mapped into a light-microscopical atlas, and Gal4 strains are being generated to experimentally access neurons one at a time. In addition, an electron microscopic reconstruction of its nervous system seems within reach. Notably, this electron microscope-based connectome is being drafted for a stage 1 larva - because stage 1 larvae are much smaller than stage 3 larvae. However, most behaviour analyses have been performed for stage 3 larvae because their larger size makes them easier to handle and observe. It is therefore warranted to either redo the electron microscopic reconstruction for a stage 3 larva or to survey the behavioural faculties of stage 1 larvae. We provide the latter. In a community-based approach we called the Ol1mpiad, we probed stage 1 Drosophila larvae for free locomotion, feeding, responsiveness to substrate vibration, gentle and nociceptive touch, burrowing, olfactory preference and thermotaxis, light avoidance, gustatory choice of various tastants plus odour-taste associative learning, as well as light/dark-electric shock associative learning. Quantitatively, stage 1 larvae show lower scores in most tasks, arguably because of their smaller size and lower speed. Qualitatively, however, stage 1 larvae perform strikingly similar to stage 3 larvae in almost all cases. These results bolster confidence in mapping brain structure and behaviour across developmental stages. The Gulbenkian/Melbourne group was supported by the Fundação para a Ciência e a Tecnologia (FCT; post-doctoral fellowship to M.J.A.-C.: SFRH/BPD/75993/2011; exploratory grant to M.J.A.-C. and C.K.M.: EXPL/BEX-BID/0497/2013). The Münster group was supported by the Cluster of Excellence Cells in Motion (CiM) and the CiM International Max Planck research school (CiM-IMPRS). The Barcelona group was supported by the Spanish Ministry of Economy and Competitiveness, 'Centro de Excelencia Severo Ochoa 2013-2017' (SEV-2012-0208), the CERCA Programme/Generalitat de Catalunya, the 'la Caixa' International PhD Programme, and the Spanish Ministry of Science and Innovation (BFU2011-26208). The LIN-GoLM group received support from the Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz, the State of Sachsen-Anhalt, the Center for Behavioral Brain Sciences Magdeburg and the Otto von Guericke Universität Magdeburg, as well as from the Deutsche Forschungsgemeinschaft (CRC 779 Motivated behaviour: B11; GE1091/4-1) and the European Commission (FP7-ICT project Miniature Insect Model for Active Learning MINIMAL). The Janelia group received support from the Howard Hughes Medical Institute. The Fribourg group was supported by a starter grant from the European Research Council (ERC-2012-StG 309832-PhotoNaviNet) and the Swiss National Science Foundation (31003A_169993). The Hamburg group was supported by the Deutsche Forschungsgemeinschaft (SPP 1926, Next generation optogenetics, SO1337/2-1), and the Landesforschungsförderung Hamburg (LFF-FV27). The LIN-MolSysBiol group received support from the Wissenschaftsgemeinschaft Gottfried Wilhelm Leibniz, the State of Sachsen-Anhalt, the Center for Behavioral Brain Sciences Magdeburg and the Deutsche Forschungsgemeinschaft (CRC 779 Motivated behaviour: B15; YA272/2-1). The Bonn group was supported by the Deutsche Forschungsgemeinschaft (PA 787/7-1) and Cluster of Excellence ImmunoSensation. The Konstanz group was supported by Deutsche Forschungsgemeinschaft (TH1584/1-1, TH1584/3-1), the Baden-Württemberg Stiftung and the Zukunftskolleg of the University of Konstanz.

Mapping brain function to brain structure is a fundamental task for neuroscience. For such an endeavour, the