A Viral Toolbox of Genetically Encoded Fluorescent Synaptic Tags

Summary Fibronectin intrabodies generated with mRNA display (FingRs) are a recently developed tool for labeling excitatory or inhibitory synapses, with the benefit of not altering endogenous synaptic protein expression levels or synaptic transmission. Here, we generated a viral vector FingR toolbox that allows for multi-color, neuron-type-specific labeling of excitatory or inhibitory synapses in multiple brain regions. We screened various fluorophores, FingR fusion configurations, and transcriptional control regulations in adeno-associated virus (AAV) and retrovirus vector designs. We report the development of a red FingR variant and demonstrated dual labeling of excitatory and inhibitory synapses in the same cells. Furthermore, we developed cre-inducible FingR AAV variants and demonstrated their utility, finding that the density of inhibitory synapses in aspiny striatal cholinergic interneurons remained unchanged in response to dopamine depletion. Finally, we generated FingR retroviral vectors, which enabled us to track the development of excitatory and inhibitory synapses in hippocampal adult-born granule cells.
Graphical Abstract
Highlights • AAV FingR vectors globally label excitatory or inhibitory synapses in neurons • AAV FingRs dually label excitatory and inhibitory synapses in the same neuron • Cre-inducible FingR AAV vectors label synapses in defined neuron populations • Retroviral FingR vectors allow tracking of synaptic development in newborn neurons
Biological Sciences; Neuroscience; Techniques in Neuroscience