2020 — 2021 |
Duan, Xin |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Mechanisms Underlying Type Ii Cadherin Guided Assembly of Retinal Circuits @ University of California, San Francisco
In the eye, complex retinal circuits are wired together for precise neural computation. The diverse but precise wiring between interneurons and retinal ganglion cells serve as the structural basis for circuit processing of different visual features. These parallel circuits are wired up precisely, as defects may lead to several eye diseases and neurological disorders. To investigate the mechanisms behind how diverse neuronal types precisely integrate into distinct parallel retinal circuits, we developed methods that allow for targeted genetic access of the unique On-Off direction-selective circuit, which conveys direction-selectivity signals, as the ideal model system. Our previous studies now position us to examine the role of Type II Cadherins (Cdhs) in assembling this circuit as individual proteins or in combinations. We showed that two Cdhs, Cdh9 and Cdh8, instruct parallel ON and OFF bipolar cell input to ON vs. OFF sublaminae of the ON-OFF direction-selective circuit, thus allowing precise segregation of ON and OFF channels. However, the molecular mechanisms underlying this assembly remain elusive. To investigate the molecular mechanisms underlying the differential functions of Cdh9 vs. Cdh8, we will perform a series of anatomical and functional analyses. We will identify the specific portion of the cadherin molecule, extracellular versus intracellular domains, that are responsible for their distinct functions, as well as the specific timing of their actions in forming synapses between bipolar cells and ganglion cells. We also found that Cdh9 from bipolar neurons heterophilically recognizes the two closely-related Cdhs, Cdh6 and Cdh10, from postsynaptic Ventral-pointing ON-OFF direction-selective ganglion cells (ooDSGCs) and starburst amacrine cells (SACs). We will use this established genetic system to reveal how combinatorial Cdhs act together to wire up parallel direction-selective circuits. We will examine genetically and functionally how Cdh6-9-10 single, double, and triple combinations pattern the Ventral-ooDSGC interaction with SACs. To further expand our understanding of the combinatorial cadherin code in neuronal patterning, we will test the role of Cdh11, which is identified as a Nasal-pointing ooDSGC enriched gene through molecular profiling. Thus, we will generate new molecularly and genetically targeted methods to examine the roles of Cdh11 and its closely related Cdh8 in the wiring of Nasal-pointing direction-selective circuits. Furthermore, we established an in utero injection system to ectopically introduce individual Type II Cdhs onto Ventral-ooDSGCs or Nasal-ooDSGCs to pinpoint combinatorial Cdhs in regulating DS-circuit patterning. Collectively, our studies seek to reveal how Cdh combinations control the formation of parallel but distinct DS circuits. Comprehensive studies on Type II Cdh function would be a major advance for a long-standing question in mammalian neural development. These studies will be a major step forward in understanding how multiple genes interact to specify the wiring of complex neural circuits. The identified mechanisms will have significant relevance to selective circuit wiring throughout the central nervous system.
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2021 |
Duan, Xin Scanziani, Massimo (co-PI) [⬀] |
R01Activity Code Description: To support a discrete, specified, circumscribed project to be performed by the named investigator(s) in an area representing his or her specific interest and competencies. |
Mapping Retinotectal Circuits For Visual-Evoked Innate Behaviors @ University of California, San Francisco
PROJECT SUMMARY The precise assembly of neural circuits ensures accurate neurological function and behavior. For example, to communicate specific aspects of the visual world to the brain, retinal ganglion cells (RGCs) find and form synaptic contacts with specific postsynaptic partners out of the heterogeneous neuronal population of retino-recipient areas in the brain. One such area is the superior colliculus (SC), which receives direct retinal inputs and sends commands for direct innate behaviors such as escape or prey capture. What are the molecular determinants for selective RGC to SC neuron wiring? How are parallel retinotectal circuits sorted onto different SC laminae and neuronal relays? How are distinct retinotectal circuits linked to defined visual evoked behaviors? This proposed study aims to answer these questions in the mouse visual system. To accomplish this goal, first, we will map out parallel retinotectal circuits. We have established an integrated anterograde-tracing and sequencing platform, Trans-Seq, that defines the outputome of a genetically- defined RGC subtype. We applied Trans-Seq to all RGC subtypes globally, ?-RGCs, and On-Off direction- selective-ganglion-cells and reconstructed their differential outputomes onto superficial superior-collicular (sSC) neuron subtypes. We propose to apply Trans-Seq to other major RGC subtypes representing different visual features. The proposed studies will determine retinotectal circuit convergence and divergence at neuron subtype resolution. Second, we aim to understand cellular and molecular mechanisms regulating specific retinotectal circuit wiring. We have analyzed ?-RGC specific outputomes and revealed a selective sSC neuron subtype, Nephronectin-positive-wide-field neurons (NPWFs). The ?-RGC-to-NPWF circuit was genetically validated using imaging, electrophysiology, and retrograde tracing. We propose to study how Nephronectin mediates ?-RGC selective axonal lamination onto the deep sSC layer and whether Nephronectin determines the subsequent synaptic specificity from ?-RGCs to NPWFs. We will also investigate what molecular mechanisms mediate Nephronectin binding and lead to a selective mammalian retinotectal circuit assembly. Third, we will link specific retinotectal circuits to defined visual evoked behaviors. We propose to combine genetic and optogenetic tools established above to determine whether the ?-RGC-to-NPWF circuit contributes to visual evoked innate behaviors, such as looming triggered defense responses. We will also examine whether molecular determinants for connectivity, such as Nephronectin, regulate this behavioral output via these retinotectal circuits. Our circuit mapping platform builds a precise connectivity map at neuronal subtype resolution. Further, this work will align the precise neuronal wiring diagram to innate visual evoked behaviors, informing future functional and behavioral analysis. The new knowledge gained here may include molecular principles underlying mammalian circuit wiring relevant beyond the visual system.
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