ER calcium handling, single cell processing, and neural circuit function in vivo

Summary Calcium is a critical second messenger in neurons, regulating neuronal processes from dendritic integration to synaptic transmission. The endoplasmic reticulum (ER) is the major intracellular calcium store in neurons, and aberrant ER calcium signaling is associated with many neurodegenerative disorders. However, it is unclear how ER calcium signaling regulates neuronal function and neural circuit stability. We aim to directly interrogate the link between ER calcium handling, single cell processing, and neural circuit function in vivo. To that end, we will take an imaging approach to simultaneously measure and manipulate physiological neuronal signals and ER calcium dynamics in the context of motion vision circuits in Drosophila. This versatile experimental system provides us with unique access to fundamental, understudied biological questions about the relationship between the ER and neuronal activity. First, the neurons that comprise Drosophila motion vision circuits exhibit a remarkable array of cytosolic calcium signals, reflecting their computational diversity. Our experimental system will allow us to investigate how calcium handling by the ER contributes to these diverse cytosolic calcium signals by comparing cytosolic and ER calcium signals across well-defined neuronal cell types in vivo. Second, neurons are extremely energetically demanding. We will leverage our in vivo imaging system to investigate the hypothesis that stimulus-evoked ER calcium signals allow neurons to upregulate ATP production in order to keep up with fluctuating energetic demands. Finally, tight control of cytosolic calcium concentration is critical for neuronal functions—including dendritic integration, synaptic plasticity, and neurotransmitter release—that control neural circuit activity and, ultimately, animal behavior. By conducting our experiments in neurons that perform specific computations critical for the function of well-defined motion vision circuits, we will be able to assess the consequences of ER manipulations not only on single cell processing, but also on large-scale neural circuit function and animal behavior. Altogether, we seek to integrate information across organizational scales—from molecules to neurons to neural circuits—to provide a mechanistic, molecular and cellular framework for understanding how ER calcium handling contributes to brain function and dysfunction.