One of the enduring mysteries of the brain is how its function can be both highly reliable, dependably controlling life-and-death decisions, and plastic, rapidly adapting to new stimuli, while maintaining these adaptations over broad timescales. Nervous system function rests on neural circuits that drive thought and behavior. Communication in neural circuits occurs at chemical synapses through neurotransmitters released by presynaptic neurons and taken up by postsynaptic partners. Thus, the assembly and modulation of synapses are foundational to nervous system function. Underscoring their critical role, synaptic dysfunction has emerged as a major component of neurological disorders ranging from intellectual disability to neurodegeneration.

Through in vivo studies in Drosophila, our lab has focused on understanding synapse formation, function, and plasticity. The remarkable conservation of synapses and synaptic genes across species coupled with the accessibility of Drosophila to genetic, imaging, in vivo cell biological, electrophysiological, and behavioral studies allow us to gain generalizable insight and advance mechanistic understanding of synapses in their endogenous contexts.

Our research focuses on two overarching goals: (i) elucidating genes and mechanisms that regulate synapse formation and plasticity and (ii) understanding how synapses are organized and reorganized for specific functions. In parallel, we have developed new gene editing tools to advance the study of synapses in vivo.

I. REGULATION OF SYNAPSE FORMATION AND FUNCTION
Aberrant synapses are a hallmark of neurodevelopmental disorders and new causative genes are being identified on a regular basis. Yet often their function in the nervous system is unknown, highlighting critical gaps in our knowledge. To identify conserved, uncharacterized regulators of synapse formation and function, we have conducted in vivo CRISPR-based screens. Our studies have revealed unexpected mechanisms for genes linked to neurodevelopmental disorders. We are currently focusing on regulators of gene expression at multiple levels.

Regulation of coordinated synaptic gene expression: Synapses are complex intercellular structures specialized for the rapid transmission of information. Building a functional synapse necessitates the interactions of hundreds of proteins across two cells. In collaboration with Dr. Erica Larschan at Brown, we have identified a critical role for DEAF1 in the coordinated repression of ~500 synaptic genes outside developmental windows of synaptogenesis to prevent excess synapse formation. Disruption of DEAF1 causes DEAF1-Associated Neurodevelopmental Disorder (DAND). We are currently collaborating with Dr. Sofia Lizarraga at Brown to translate our findings to human iPSC-derived neurons and brain organoids.

RNA modification and synapse formation & function: Posttranscriptional modification of RNAs has emerged as a key regulator of protein synthesis. tRNAs are central components of the translational machinery that decode mRNA by linking codons to corresponding amino acids and are the most heavily modified RNA. Post-transcriptional tRNA modification regulates tRNA structure, stability, codon recognition, and decoding speed. Because tRNA modifications determine which codons are efficiently decoded, the dynamic modulation of tRNA modifications can modulate which mRNAs are efficiently translated based on differential codon usage.

We have discovered roles for tRNA-modifying enzymes in regulating synapse formation and plasticity. In recent years, at least 10 tRNA modifying enzymes have been linked to neurodevelopmental disorders, underscoring their critical importance in nervous system development. In collaboration with Dragony Fu’s lab (University of Rochester), we are combining in vivo phenotypic and mechanistic studies in Drosophila with studies in iPSC-derived neurons and brain organoids. Through our collaboration with Juan Alfonzo’s lab at Brown, we are conducting systematic studies of the dynamic regulation of tRNA modifications in nervous system development and their impact on translation.

Regulation of activity-dependent synapse formation at membrane contact sites: The formation and function of synaptic connections require coordinating a host of cellular activities, placing a high demand on intracellular communication. This high demand coupled with the polarized structure and long distances between synapses and the cell body present unique challenges for neurons. Sites of close apposition between cellular organelles, called membrane contact sites (MCSs), have emerged as key signaling hubs for coordinating an array of cellular activities. MCS disruption underlies a number of neurological disorders, indicating critical roles in the nervous system.

In our screens, we identified the MCS tethering protein PDZD8 as a regulator of activity-dependent synapse formation. PDZD8, which has been implicated in a rare intellectual disability, is an intrinsic endoplasmic reticulum (ER) lipid transfer protein found at ER-late endosome/lysosome (LEL) and ER-mitochondrial MCSs. We discovered that PDZD8 functions at neuronal ER-LEL MCSs to promote lysosome maturation and accelerate autophagy during periods of high demand, such as intense or prolonged neuronal activity. Through a collaboration with Arash Bashirullah’s lab (University of Houston), we are studying how a second MCS protein, bulk lipid transporter BLTP2, regulates nervous system development and function.

II. DETERMINANTS OF DYNAMIC SYNAPTIC PROPERTIES
We have a long-standing interest in understanding how synapses are molecularly and spatially organized to achieve specific properties. At chemical synapses, neurotransmitter release occurs when action potentials drive the opening of voltage-gated Ca²⁺ channels and trigger Ca²⁺-dependent fusion of neurotransmitter-filled synaptic vesicles. Synaptic strength, or the likelihood of neurotransmitter release in response to an action potential, is dynamic and varies considerably between neuronal connections, enabling complex communication and broadening the capacity of circuits to reliably transmit information and respond to changing inputs.

Determining how diversity in synaptic strength is established is a major goal of the field. Our studies have revealed local regulators of dynamic synapse organization; molecular and nanoscale organizational parameters underlying diverse presynaptic release properties; and how these parameters are dynamically modulated to maintain reliable communication.

We have generated a full complement of Drosophila lines with functional endogenously tagged calcium channel subunits, allowing us and others to investigate of calcium channel dynamics in vivo. With these tools, we demonstrated that calcium channel abundance and stoichiometry at synaptic terminals predicts synaptic strength and can be rapidly modulated. Through collaborative studies with Dion Dickman’s lab (University of Southern California), we are conducting comprehensive studies of how channel complex composition contributes to diversifying synaptic properties and plasticity across the nervous system. Through our collaboration with Heather Broihier’s lab (Case Western Reserve University), we have investigated the coordinated development of pre- and post-synaptic compartments. In collaboration with Karla Kaun’s lab at Brown, we are investigating the role of alternative splicing in modulating neural circuits underlying reward memory in response to alcohol.

GENE EDITING TOOLS
Genetic and molecular techniques to manipulate the genomes of organisms are invaluable tools for understanding gene function. In collaboration with the Wildonger and Harrison labs, we developed CRISPR-Cas9 gene editing in Drosophila. We have prioritized the rapid, open dissemination of the CRISPR tools and methods we develop and have distributed thousands of plasmids and fly lines through nonprofit repositories. We created a web tool for identifying and evaluating CRISPR targets that is widely used by researchers around the world. We have developed a pipeline for in vivo CRISPR genetic screens and are currently focused on developing approaches to observe endogenous proteins in subsets of their patterns in dense tissues such as the brain.

NIH NINDS Landis Award for Outstanding Mentorship, 2021

NIH NINDS Landis Award for Outstanding MentorshipMcKnight Foundation Technological Innovations in Neuroscience Award, 2014-2016

NIH NINDS K99/R00 Pathway to Independence Award, 2008-2012                     

DeLill Nasser Award for Professional Development in Genetics, 2008                               

Jane Coffin Childs Memorial Fund Postdoctoral Fellowship, 2004-2007                     

Spencer T. and Ann W. Olin Medical Scientist Fellow, 2002

Carney Institute for Brain Science
Giuliani RNA Center
Trainer, Neuroscience Graduate Program
Trainer, Molecular Biology, Cell Biology and Biochemistry Graduate Program
Trainer, Therapeutic Sciences
Trainer, Center for Cellular & Molecular Biology

Communication in the nervous system occurs primarily through chemical synapses. In this seminar style course, we explore the cellular and molecular underpinnings of synapse formation, neurotransmission, synaptic plasticity, and neural circuit function through deep interrogation of primary literature and activities based on open questions in the field and the latest approaches for addressing them. Students build a solid foundation for deep understanding and critical evaluation of primary literature; experimental design and interpretation; and scientific communication while broadening their understanding of approaches in modern neuroscience through an emphasis on how the field investigates synapses and circuits across distinct levels of interrogation.