Biology subjects

Michel, J. C.

Publications and source records attributed to Michel, J. C..

6 recordsLinked to original sources

bioRxiv2024

Electrical synapse molecular diversity revealed by proximity-based proteomic discovery

Neuronal circuits are composed of synapses that are either chemical, where signals are transmitted via neurotransmitter release and reception, or electrical, where signals pass directly through interneuronal gap junction channels. While the molecular complexity that controls chemical synapse structure and function is well appreciated, the proteins of electrical synapses beyond the gap-junction-forming Connexins are not well defined. Yet, electrical synapses are expected to be molecularly complex beyond the gap junctions. Connexins are integral membrane proteins requiring vesicular transport and membrane insertion/retrieval to achieve function, homeostasis, and plasticity. Additionally, electron microscopy of neuronal gap junctions reveals neighboring electron dense regions termed the electrical synapse density (ESD). To reveal the molecular complexity of the electrical synapse proteome, we used proximity-dependent biotinylation (TurboID) linked to neural Connexins in zebrafish. Proteomic analysis of developing and mature nervous systems identifies hundreds of Connexin-associated proteins, with overlapping and distinct representation during development and adulthood. The identified protein classes span cell adhesion molecules, cytoplasmic scaffolds, vesicular trafficking, and proteins usually associated with the post synaptic density (PSD) of chemical synapses. Using circuits with stereotyped electrical and chemical synapses, we define molecular sub-synaptic compartments of ESD localizing proteins, we find molecular heterogeneity amongst electrical synapse populations, and we examine the synaptic intermingling of electrical and chemical synapse proteins. Taken together, these results reveal a new complexity of electrical synapse molecular diversity and highlight a novel overlap between chemical and electrical synapse proteomes. Moreover, human homologs of the electrical synapse proteins are associated with autism, epilepsy, and other neurological disorders, providing a novel framework towards understanding neuro-atypical states.

neuroscience↗

bioRxiv2022

The disconnect2 mutation disrupts the tjp1b gene that is required for electrical synapse formation

To investigate electrical synapse formation in vivo we used forward genetics to disrupt genes affecting Mauthner cell electrical synapses in larval zebrafish. We identify the disconnect2 (dis2) mutation for its failure to localize neural gap junction channels at electrical synapses. We mapped this mutation to chromosome 25 and identified a splice-altering mutation in the tjp1b gene. We demonstrated that the dis2 mutation disrupts tjp1b function using complementation analysis with CRISPR generated mutants. We conclude that the dis2 mutation disrupts the tjp1b gene that is required for electrical synapse formation. DescriptionNeural networks are circuits of neurons wired together during development that provide an animal with specialized behavioral outputs. Dedicated adhesions called neuronal synapses create sites of communication between neurons and can be categorized as either electrical or chemical. This work identifies a new mutation in tjp1b that is shown to be required for electrical synapse formation.

genetics↗

bioRxiv2022

ZO1 scaffold isoforms differentially contribute to electrical synapse formation

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 proteomic makeup and molecular mechanisms utilized by the ESD that direct electrical synapse 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 GJ channel localization, electrical communication, neural network function, and behavior. 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 and ZO1b-Gamma are broadly expressed throughout the nervous system and localize to electrical synapses. By contrast, ZO1b-Alpha is expressed mainly non-neuronally and is not found at synapses. We generate mutants in all individual isoforms, as well as double mutant combinations in cis on individual chromosomes, and find that ZO1b-Beta is necessary and sufficient for robust GJ channel localization. ZO1b-Gamma, despite its localization to the synapse, plays an auxiliary role in channel localization. This study expands the notion of molecular complexity at the ESD, revealing that an individual genomic locus can contribute distinct isoforms to the macromolecular complex at electrical synapses. Further, independent scaffold isoforms have differential contributions to developmental assembly of the interneuronal GJ channels. We propose that ESD molecular complexity arises both from the diversity of unique genes and from distinct isoforms encoded by single genes. Overall, ESD proteomic diversity is expected to have critical impacts on the development, structure, function, and plasticity of electrical transmission.

neuroscience↗

bioRxiv2022

Neurobeachin controls the asymmetric subcellular distribution of electrical synapse proteins

The subcellular positioning of synapses and their specialized molecular compositions form the fundamental basis of neural circuits. Like chemical synapses, electrical synapses are constructed from an assortment of adhesion, scaffolding, and regulatory molecules, yet little is known about how these molecules localize at specified subcellular neuronal compartments. Here we investigated the relationship between the autism- and epilepsy-associated gene Neurobeachin, neuronal gap junction channelforming Connexins, and the scaffold ZO1. Using the zebrafish Mauthner circuit we found Neurobeachin localizes to the electrical synapse independent of ZO1 and Connexins. By contrast, we show Neurobeachin is required postsynaptically for the robust localization of ZO1 and Connexins. We demonstrate Neurobeachin binds ZO1 but not Connexins. Finally, we find Neurobeachin is required to restrict postsynaptic electrical synapse proteins to dendrites. These findings reveal a mechanism for the asymmetric synaptic localization of electrical synapse components providing a basis for the subcellular specialization of neuronal gap junctions.

neuroscience↗

bioRxiv2020

Electrical synaptic transmission requires a postsynaptic scaffolding protein

Electrical synaptic transmission relies on neuronal gap junctions containing channels constructed by Connexins. While at chemical synapses neurotransmitter-gated ion channels are critically supported by scaffolding proteins, it is unknown if channels at electrical synapses require similar scaffold support. Here we investigated the functional relationship between neuronal Connexins and Zonula Occludens 1 (ZO1), an intracellular scaffolding protein localized to electrical synapses. Using model electrical synapses in zebrafish Mauthner cells, we demonstrated that ZO1 is required for robust synaptic Connexin localization, but Connexins are dispensable for ZO1 localization. Disrupting this hierarchical ZO1/Connexin relationship abolishes electrical transmission and disrupts Mauthner-cell-initiated escape responses. We found that ZO1 is asymmetrically localized exclusively postsynaptically at neuronal contacts where it functions to assemble intercellular channels. Thus, forming functional neuronal gap junctions requires a postsynaptic scaffolding protein. The critical function of a scaffolding molecule reveals an unanticipated complexity of molecular and functional organization at electrical synapses.

neuroscience↗

bioRxiv2017

Asymmetry of an intracellular scaffold at vertebrate electrical synapses

Neuronal synaptic connections are electrical or chemical and together are essential to dynamically defining neural circuit function. While chemical synapses are well known for their biochemical complexity, electrical synapses are often viewed as comprised solely of neuronal gap junction channels that allow direct ionic and metabolic communication. However, associated with the gap junction channels are structures observed by electron microscopy called the Electrical Synapse Density (ESD). The ESD has been suggested to be critical for the formation and function of the electrical synapse, yet the biochemical makeup of these structures is poorly understood. Here we find that electrical synapse formation in vivo requires an intracellular scaffold called Tight Junction Protein 1b (Tjp1b). Tjp1b is localized to electrical synapses where it is required for the stabilization of the gap junction channels and for electrical synapse function. Strikingly, we find that Tjp1b protein localizes and functions asymmetrically, exclusively on the postsynaptic side of the synapse. Our findings support a novel model in which there is molecular asymmetry at the level of the intracellular scaffold that is required for building the electrical synapse. ESD molecular asymmetries may be a fundamental motif of all nervous systems and could support functional asymmetry at the electrical synapse.

neuroscience↗