Institute of Neuroscience Faculty
Assistant Professor, Department of Biology
Ph.D., University of Oregon
Postdoc, Fred Hutchinscon Cancer Research Center
Neural circuit wiring, synapse formation, and electrical synaptogenesis in zebrafish.
The human brain contains more connections between neurons than the Milky Way has stars! The brain is wired at a gross level into stereotyped neural circuits that underlie sensation, information processing, motor output, and ultimately, consciousness. Disrupted neural circuitry has been linked to many neurodevelopmental disorders, such as autism, epilepsy, and schizophrenia. How do the neurons of the brain connect and wire up into circuits? The goal of the research in the lab is to integrate genetics, biochemistry, cell biology, circuit function, and behavior, to understand how the brain creates functioning neural networks.
Neural circuits are defined by the connections made between neurons, and 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. While the last decade has provided much insight into the developmental genetic mechanisms of building chemical synapses, electrical synapse formation is still not 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.
Using zebrafish as a model system we have performed a forward genetic screen to identify mutations that cause defects in electrical synapse formation. Mapping mutations from forward genetic screens is challenging, particularly in large vertebrate genomes, but we have developed methods using on next generation sequencing which facilitate the identification of mutated genes (Genome Research). One of the mutations identified in the screen disrupted the autism-associated gene neurobeachin and we found that it was required for both electrical and chemical synapse formation, placing this gene as a critical lynchpin in all of synapse formation (Current Biology). We have also developed a novel CRISPR-based reverse genetic screening method to identify genes required for development – this was the first example that such an approach could be taken in a vertebrate (Nature Methods). The screen identified structural proteins that create the gap junction channel between the neurons and scaffolding that stabilize the synaptic structure. Ongoing work has revealed that electrical synapses can be asymmetric, with unique proteins on each side of the junction. This molecular asymmetry may underlie functional asymmetry and provide differential substrates for altering electrical synapse function.
Current projects focus on several diverse, but related, areas of electrical synaptogenesis:
1) Electrical synapse asymmetry – biochemistry, molecular biology, and genetics
How do the proteins of the synapse function at the molecular level to form the connection? What proteins interact and how do those interactions build the synapse? What other proteins are present at the synapse?
2) Electrical synapse formation – cell biology, development, and genetics
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?
3) Electrical synapse function – behavior and physiology
Does the 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?
4) Electrical and chemical synapse interactions – physiology, development, and genetics
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?
• Shah AN, Davey CF, Whitebirch AC, Moens CB^, Miller, AC^ (2015). Reverse genetic screening using CRISPRs in zebrafish. Nature Methods doi:10.1038/nmeth.3360.
• Finley JK, Miller AC, Herman TG (2015). Polycomb group genes are required to maintain a binary fate choice in the Drosophila eye. Neural Development 10(1):2.
• Miller AC, Voelker L, Shah AN, Moens CB (2015). Neurobeachin is required autonomously by the postsynaptic for electrical and chemical synapse formation. Current Biology 2015 25(1):16-28. o Featured in Dispatch by Pereda A. Current Biology 25(1):R38-41.
• Miller AC, Obholzer ND, Shah AN, Megason SG, Moens CB (2013). RNA-seq based mapping and candidate identification of mutations from forward genetic screens. Genome Research 23(4):679-86. o Highlighted by Burgess D. Nature Reviews Genetics 14(3), 154-155.
• Miller AC, Lyons E, Herman TG (2009). cis-inhibition of Notch by endogenous Delta biases the outcome of lateral inhibition. Current Biology 19(16), 1378-83. o Featured in Dispatch by del Alamo D and Schwisguth F. Current Biology 19(16):F683-4.
• Miller AC, Seymour H, King C, Herman TG (2008). Loss of seven-up from Drosophila R1/R6 photoreceptors reveals a stochastic fate choice that is normally biased by Notch. Development 135(4), 707-15
• Faumont S, Miller AC, and Lockery SR (2005). Chemosensory behavior of semi-restrained Caenorhabditis elegans. Journal of Neurobiology 65(2), 171-8.
• Miller AC*, Thiele TR*, Faumont S*, and Lockery SR (2005). Step-response analysis of chemotaxis in Caenorhabditis elegans. Journal of Neuroscience 25(13), 3369-78.
• Zariwala HA*, Miller AC*, Faumont S*, and Lockery SR (2003). Step response analysis of thermotaxis in Caenorhabditis elegans. Journal of Neuroscience 23(10), 4369-4377.
(* denotes co-first authorship, ^ denotes co-senior authorship)