Mechanisms underlying CD3ζ guided assembly of retinal circuits

University Of Utah, Salt Lake City UT

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Abstract

The mammalian nervous system is composed of billions of neurons, and the precise assembly of these neurons into circuits ensures proper functionality. In the retina, the diverse but precise wiring between bipolar cells (BCs) and retinal ganglion cells (RGCs) serve as the structural basis for circuit processing of visual signals from outer retina to the inner retina. Defects in these wirings lead to severe retinal diseases. The most common example of these diseases is glaucoma, which imputes a significant social and economic burden on the US population. A major obstacle to developing effective therapies to regenerate BC to RGC wirings is our poor understanding of the structure of these circuits and the mechanisms ensuring BCs and RGCs to wire up precisely. In this proposal, we illustrate the cellular strategy of function specific BC to RGC wiring and how CD3? selectively instruct RGCs to target various BC types for wiring. To illustrate the assembly of function-specific circuits, we developed a novel transcellular labeling technique to label BCs synaptically wired to function-specific RGCs. Our results on a specific type of DS-RGCs, BD-RGCs, are comparable to those from EM connectomic studies. Our results also show that two different RGC types synapse with distinct BC types, suggesting RGC type-specific wiring with BC types. These studies position us to examine more RGC types and to reveal the underlying mechanisms guiding the assemble of each RGC type with various BC types. Toward this end, we found that mutation of CD3?, a receptor for class I major histocompatibility complex (MHCI), eliminates synaptic connections of cone BCs to BD-RGCs but increase synaptic connections of cone BCs to J-RGCs, thus allowing RGC type-specific synaptic regulation. The defects in synaptic wiring of cone BCs to BD-RGCs in CD3? mutants significantly impair the light-evoked responses of BD-RGCs, suggesting that precise BC-RGC synaptic wirings are necessary to ensure function specificity of RGCs. To further test this idea, we will identify the BC types wired to additional 4 RGC types and the synaptic function of these RGCs to reveal the cellular strategy responsible for specifying RGC function. We will also examine how CD3? instructs synapse formation and function of these RGCs. To uncover the mechanisms underlying CD3?-mediated synaptic assembly, we showed that knockdown or overexpress CD3? in RGCs of wildtype mice or CD3? mutants only induced phenotypes in transduced RGCs, suggesting a cell-autonomous mechanism. To further expand our understanding of the mechanisms, we will perform a series analyses to determine whether CD3? is specifically required for the dendritic development of RGCs, whether it is sufficient for the dendritic development of RGCs, and whether it is required to maintain dendritic stability in adults. Thus, we will examine the roles of CD3? in the BCs to RGCs wiring using our newly generated molecular and genetic tools. Collectively, our studies seek to reveal the strategy and mechanisms that control RGCs type-specific circuit formation. These studies will constitute a significant step forward in understanding the mechanisms underlying the development of function-specific circuits.