Electrical Synapse Formation

Neural circuits are defined by the connections made between neurons. The connections, termed synapses, come in two flavors: chemical, where transmission is mediated by neurotransmitters and receptors, and electrical, where neurons directly communicate with one another through gap junction channels. The latter are less well understood. However, it is known that electrical synapses are used by all animals both during development and in adulthood, and are found in sensory, central, and motor circuits. The goal of this project is to unlock the molecular mechanisms underlying electrical synaptogenesis.We use the zebrafish Mauthner circuit as a model system and utilize both forward and reverse genetic techniques to identify mutations that cause defects in electrical synapse formation. One of the mutations identified disrupted the autism-associated gene neurobeachin and, surprisingly, we found that it was required for both electrical and chemical synapse formation. This places neurobeachin as a critical lynchpin in all of synapse formation (Current Biology). We develop resources that help to speed the discovery of gene function in zebrafish. In one, we created a faster way to identify mutations from forward genetic screens (Genome Research). In another we developed a novel CRISPR-based reverse genetic screening method. This was the first example that such an approach could be taken in a vertebrate (Nature Methods). Ongoing work has revealed that electrical synapses can be asymmetric, with unique proteins on each side of the junction. We now want to understand the functional consequences of such asymmetry. Current projects focus on:

1) Electrical synapses

- Asymmetry

We have found that gap junction proteins are asymmetrically distributed at Mauthner synapses. How do the proteins of the synapse function at the molecular level to form this asymmetric connection? What proteins interact and how do those interactions build the synapse? What other proteins are present at the synapse and do they function asymmetrically?

- Formation

How are proteins trafficked to the synapse? How are they captured and stabilized once present? What are the cytoskeletal structures and motor proteins that facilitate movement? How long do proteins remain at the synapse and are they responsive to neuronal activity?

- Function

Does the molecular composition of the electrical synapse change based on circuit activity? Do molecular asymmetries produce effects on synapse function? How are molecular asymmetries integrated into circuit level function and behavioral output?

2) Synaptic balance

- Neural circuit prepatterning

How are early-forming electrical synapses required for subsequent chemical synapse formation? What gap junction channels and scaffolds mediate early circuit activity? How are some early-forming electrical synapses removed as neural circuits mature? How are others retained?

- Electrical and chemical synapse interactions

How does Neurobeachin control both electrical and chemical synapse formation? How do electrical synapses contribute to E/I balance in the brain? How does a single neuron 'choose' to make electrical synapses with some targets, but chemical with others?

3) Cell Atlas of zebrafish using scRNA-seq

- Development

How does gene expression change across development in an entire vertebrate? What are all the cell types? What are all the developmental trajectories?

- Adult

What are all the cell types and all the cell states present in the adult vertebrate? How similar are these tissues to those found in other animals (mouse, human)?

- Bioinformatic tools

How can we efficiently categorize cell types across a complex vertebrate? How can we integrate new data into existing?

- ZFIN integration

What is the best way to make all of the data accessible and useful to the community?