Optogenetic delivery of trophic signals in a genetic model of Parkinson's disease

Invertebrate genetic models of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a common adult-onset neurodegenerative disease characterized by the progressive death of motor neurons in the cerebral cortex, brain stem, and spinal cord. The exact mechanisms underlying the pathogenesis of ALS remain unclear. The current consensus regarding the pathogenesis of ALS suggests that the interaction between genetic susceptibility and harmful environmental factors is a promising cause of ALS onset. The investigation of putative harmful environmental factors has been the subject of several ongoing studies, but the use of transgenic animal models to study ALS has provided valuable information on the onset of ALS. Here, we review the current common invertebrate genetic models used to study the pathology, pathophysiology, and pathogenesis of ALS. The considerations of the usage, advantages, disadvantages, costs, and availability of each invertebrate model will also be discussed.

Optimized design and in vivo application of optogenetically functionalized Drosophila dopamine receptors

Neuromodulatory signaling via G protein-coupled receptors (GPCRs) plays a pivotal role in regulating neural network function and animal behavior. The recent development of optogenetic tools to induce G protein-mediated signaling provides the promise of acute and cell type-specific manipulation of neuromodulatory signals. However, designing and deploying optogenetically functionalized GPCRs (optoXRs) with accurate specificity and activity to mimic endogenous signaling in vivo remains challenging. Here we optimize the design of optoXRs by considering evolutionary conserved GPCR-G protein interactions and demonstrate the feasibility of this approach using two Drosophila Dopamine receptors (optoDopRs). These optoDopRs exhibit high signaling specificity and light sensitivity in vitro. In vivo, we show receptor and cell type-specific effects of dopaminergic signaling in various behaviors, including the ability of optoDopRs to rescue the loss of the endogenous receptors. This work demonstrates that optoXRs can enable optical control of neuromodulatory receptor-specific signaling in functional and behavioral studies.

Optogenetic dissection of RET signaling reveals robust activation of ERK and enhanced filopodia-like protrusions of regenerating axons

RET (REarranged during Transfection) is a receptor tyrosine kinase that transduces various external stimuli into biological functions, such as survival and differentiation, in neurons. In the current study, we developed an optogenetic tool for modulating RET signaling, termed optoRET, combining the cytosolic region of human RET with a blue-light-inducible homo-oligomerizing protein. By varying the duration of photoactivation, we were able to dynamically modulate RET signaling. Activation of optoRET recruited Grb2 (growth factor receptor-bound protein 2) and stimulated AKT and ERK (extracellular signal-regulated kinase) in cultured neurons, evoking robust and efficient ERK activation. By locally activating the distal part of the neuron, we were able to retrogradely transduce the AKT and ERK signal to the soma and trigger formation of filopodia-like F-actin structures at stimulated regions through Cdc42 (cell division control 42) activation. Importantly, we successfully modulated RET signaling in dopaminergic neurons of the substantia nigra in the mouse brain. Collectively, optoRET has the potential to be developed as a future therapeutic intervention, modulating RET downstream signaling with light.

Shedding light on current trends in molecular optogenetics

Molecular optogenetics is a highly dynamic research field. In the past two years, the field was characterized by the development of new allosteric switches as well as the forward integration of optogenetics research towards application. Further, two areas of research have significantly gathered momentum, the use of optogenetics to control liquid-liquid phase separation as well as the application of optogenetic tools in the extracellular space. Here, we review these areas and discuss future directions.

Regenerative Strategies for Retinal Neurons: Novel Insights in Non-Mammalian Model Organisms

A detailed knowledge of the status of the retina in neurodegenerative conditions is a crucial point for the development of therapeutics in retinal pathologies and to translate eye research to CNS disease. In this context, manipulating signaling pathways that lead to neuronal regeneration offers an excellent opportunity to substitute damaged cells and, thus, restore the tissue functionality. Alternative systems and methods are increasingly being considered to replace/reduce in vivo approaches in the study of retina pathophysiology. Herein, we present recent data obtained from the zebrafish (Danio rerio) and the fruit fly Drosophila melanogaster that bring promising advantages into studying and modeling, at a preclinical level, neurodegeneration and regenerative approaches in retinal diseases. Indeed, the regenerative ability of vertebrate model zebrafish is particularly appealing. In addition, the fruit fly is ideal for regenerative studies due to its high degree of conservation with vertebrates and the broad spectrum of genetic variants achievable. Furthermore, a large part of the drosophila brain is dedicated to sight, thus offering the possibility of studying common mechanisms of the visual system and the brain at once. The knowledge acquired from these alternative models may help to investigate specific well-conserved factors of interest in human neuroregeneration after injuries or during pathologies.

Light-activated receptor tyrosine kinases: Designs and applications

Receptor tyrosine kinases (RTKs) are a large and essential membrane receptor family. The molecular mechanisms and physiological consequences of RTK activation depend on, for example, ligand identity, subcellular localization, and developmental or disease stage. In the past few years, genetically-encoded light-activated RTKs (Opto-RTKs) have been developed to dissect these complexities by providing reversible and spatio-temporal control over cell signaling. These methods have very recently matured to include highly-sensitive multi-color actuators. The new ability to regulate RTK activity with high precision has been recently harnessed to gain mechanistic insights in subcellular, tissue, and animal models. Because of their sophisticated engineering, Opto-RTKs may only mirror some aspects of natural activation mechanisms but nevertheless offer unique opportunities to study RTK signaling and physiology.

A neuropeptidergic circuit gates selective escape behavior of Drosophila larvae

Animals display selective escape behaviors when faced with environmental threats. Selection of the appropriate response by the underlying neuronal network is key to maximizing chances of survival, yet the underlying network mechanisms are so far not fully understood. Using synapse-level reconstruction of the Drosophila larval network paired with physiological and behavioral readouts, we uncovered a circuit that gates selective escape behavior for noxious light through acute and input-specific neuropeptide action. Sensory neurons required for avoidance of noxious light and escape in response to harsh touch, each converge on discrete domains of neuromodulatory hub neurons. We show that acute release of hub neuron-derived insulin-like peptide 7 (Ilp7) and cognate relaxin family receptor (Lgr4) signaling in downstream neurons are required for noxious light avoidance, but not harsh touch responses. Our work highlights a role for compartmentalized circuit organization and neuropeptide release from regulatory hubs, acting as central circuit elements gating escape responses.