pharmacological treatment of mental disorders is currently decided based on "trial and error" strategy. Mitochondrial multifaceted dysfunction is assumed to be a major factor in the pathophysiology and treatment of schizophrenia (SZ) and bipolar disorder (BD). This study aimed to explore the feasibility of using a profile of mitochondrial function parameters as a tool to predict the optimal drug for an individual patient (personalized medicine). Healthy controls (n = 40), SZ (n = 48) and BD (n = 27) patients were recruited. Mental and global state of the subjects, six mitochondrial respiration parameters and 14 mitochondrial function-related proteins were assessed in fresh lymphocytes following in-vitro or in-vivo treatment with five antipsychotic drugs and two moodstabilizers. In healthy controls, hierarchal clustering shows a drug-specific effect profile on the different mitochondrial parameters following in-vitro exposure. Similar changes were observed in untreated SZ and BD patients with psychosis. Following a month of treatment of the latter patients, only responders showed a significant correlation between drug-induced in-vitro effect (prior to in-vivo treatment) and short-term in-vivo treatment effect for 45% of the parameters. Long-but not shortterm psychotropic treatment normalized mitochondria-related parameters in patients with psychosis. Taken together, these data substantiate mitochondria as a target for psychotropic drugs and provide a proof of concept for selective mitochondrial function-related parameters as a predictive tool for an optimized psychotropic treatment in a given patient. This, however, needs to be repeated with an expanded sample size and additional mitochondria related parameters. Schizophrenia (SZ) and bipolar-disorder (BD) share emotional and cognitive abnormalities and psychotic symptoms, commonly affecting young adults. Both disorders also share genetic risks and endophenotypes 1-3. The research domain criteria (RDoC), based on observable behavioral (symptoms) and neurobiological dimensions rather than traditional diagnostic measures 4 claims a lack of clear boundaries between SZ and BD. Henceforth, in the present study, we studied SZ and BD as a single entity 5. More than 40 different antipsychotic and mood stabilizing drugs are currently available. It has long been held that there is little difference in the therapeutic efficacy of antipsychotics other than clozapine and differences in clinical effects were mainly ascribed to variability in sedative and adverse effect profiles. The truth of this assertion

Emerging genetically-encoded Ca 2+-indicators (GECIs) are intensiometric reporters that increase in fluorescence when bound to Ca 2+ ; highly suited for studying calciumsignaling in many cell types, notably neurons. Today, major efforts are devoted toward optimizing red-emitting [red fluorescent protein (RFP)-based] GECIs (R-GECI), as these provide several advantages over GFP-based reporters, for instance, increased imaging depth, reduced photodamage by longer imaging wavelengths and, in principle, are better suited for use with prevalent blue-absorbing optogenetic tools (e.g., channelrhodopsin). However, excessive fluorescence from intersecting neighboring cells in very dense tissues, notably the brain, hinders the ability to collect signals from single cells and their processes. This challenge can be addressed by photoactivatable (PA) fluorescent proteins that can be rendered fluorescent on demand by user-defined targeted light. This allows activation and, thereby, collection of fluorescent signals exclusively from desired cells and their processes, while leaving all neighboring cells in the dark (i.e., non-fluorescent). Nevertheless, there are no PA R-GECIs. Here, we sought to develop PAR -GECIs. To do so, we initially explored a recently discovered phenomenon of Ca 2+-independent increases in fluorescence (i.e., artifacts) in an emerging R-GECI, which has led us to rationally engineer several functional PAR -GECIs. We also take advantage of our findings to quickly engineer a novel PA-RFP, namely, PA-mRuby3.

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We assessed the feasibility of using stop codons as means to obtain polycistronic expression in eukaryotic cells. We show robust bicistronic expression of different open reading frames (ORFs), when these are cloned in sequence and simply separated by stop codons (in or out of frame), in heterologous expression systems and primary neurons. We further find this method to support polycistronic expression of three stop codon separated ORFs in vivo, which guided us to develop a technicolor Genetically Encoded Functional Rainbow Indicators (GEFRIs) for monitoring cellular morphology and neuronal firing, concomitantly. These findings guided us to develop a new technique we denote SPLIT: Stop codon mediated Polycistronic Induction in HeTerologous expression systems, for rapid and easy development of fragmented proteins by the sole use of stop codons. We validated the SPLIT method by generating several new split-GFP variants, then engineer a palette of functional split-GCaMP6s variants and, lastly, generate a split ca2+-probe localized at ER and mitochondria junctions, denoted split-MEGIC. With the use of the probe, we show presence and activity of mito-ER contact sites within individual dendritic spines. Split MEGIC can thereby be imaged by two photon excitation in vivo in mice brains and, by standard confocal microscope in transgenic zebrafish larvae. Together, we explore non canonical translation mechanisms and show these to be highly pervasive in various cell types in vitro and in vivo. We harness translation reinitiation to express multiple ORFs, to engineer rainbow indicators and to swiftly produce functional split-proteins and probes.