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Electrical synapses are neuronal gap junction (GJ) channels associated with a macromolecular complex called the electrical synapse density (ESD), which regulates development and dynamically modifies electrical transmission. However, the molecular mechanisms of ESD formation are not well understood. Using the Mauthner cell of zebrafish as a model, we previously found that the intracellular scaffolding protein ZO1b is a member of the ESD, localizing postsynaptically, where it is required for channel localization, electrical communication, neural network function, and behavior (Lasseigne et al., 2021). Here, we show that the complexity of the ESD is further diversified by the genomic structure of the ZO1b gene locus. The ZO1b gene is alternatively initiated at three transcriptional start sites resulting in isoforms with unique N-termini that we call ZO1b-Alpha, -Beta, and -Gamma. We demonstrate that ZO1b-Beta is localized to electrical synapses where it is necessary and sufficient for robust channel localization. Additionally, ZO1b-Gamma is also localized to synapses, yet plays a minor role in channel localization. By contrast, ZO1b-Alpha plays no role at the developmental stage examined. This study expands the notion of molecular complexity at the ESD, revealing that an individual genomic locus can contribute multiple independent isoforms to the macromolecular complex at the synapse with each differentially contributing to structural formation. We propose that ESD molecular complexity arises both from the diversity of unique genes and from distinct isoforms encoded by single genes, and that such proteomic diversity has critical impacts on the structure, function, and plasticity of electrical transmission. |
