Our long-term goal is to find out how axons in the vertebrate brain determine when and where to form synapses. We focus on laminar specificity, a fundamental determinant of connectivity throughout the brain, whereby neuronal processes confine their arbors and synapses to specific laminae within a target area. Our object of study is the retinal ganglion cell (RGC), because it is relatively accessible, has a well-defined function, and displays exquisite laminar specificity: axons of distinct RGC subsets synapse in specific sublaminae of the optic tectum's retinorecipient lamina (RRL), and their dendrites arborize in specific sublaminae of the inner plexiform layer (IPL), where they receive inputs from lamina-specified subsets of amacrine and bipolar cells. In work supported by this grant, we have identified several molecules likely to regulate laminar selectivity in retina, and now propose to investigate the mechanisms by which they act: (i) We found that four related immunoglobulin superfamily (IgSF) adhesion molecules, Sidekicks-1, Sidekick-2, Dscam and DscamL are critical determinants of an IgSF code that underlies some aspects of sublaminar specificity in the IPL. We will now assess their mechanisms of action and use transgenic methods to mark and manipulate the cells in which they are expressed. (ii) In a search for additional IgSF molecules in retina, we found that JAM-B is expressed by a subset of RGCs, generated mice in which these cells are indelibly labeled, and showed that JAM-B marks a unique population of lamina-specified cells sensitive to upward motion. We will now follow the development of this population, and ask whether JAM-B helps determine their structure or function. (iii) A family of ~60 protocadherins, has been proposed to mediate synaptic specificity in the retina and elsewhere. We previously demonstrated synaptic defects in mice lacking all 22 genes of the gamma protocadherin cluster, but analysis was complicated by neonatal lethality. We have now obtained conditional mutants that are healthy but have defects in retina, so we can directly assess its role. Finally, we will return to studies of laminar targeting in tectum, to determine the relationship between lamina-specific choices made by dendrites and axons of single cells. We will assess roles of Type II cadherins in tectum, and use a novel multicolor transgenic strategy to document laminar patterns of RGC axonal arbors in mouse superior colliculus. Using these strategies we hope to elucidate mechanisms that promote lamina-specific synapse formation and, by extension, synaptic specificity generally. NARRATIVE During development, neurons connect with each other in very specific ways, forming the complex circuits that underlie our mental activities. Our long-term goal is to find some of the cells and molecules that determine when and where these connections, called synapses, form. We are focusing on a particular process called laminar specificity, whereby neuronal processes confine their arbors and synapses to specific slab-like laminae within a target area. Our object of study is the retinal ganglion cell (RGC), the neuronal type that carries visual information from the eye to the brain: it is relatively accessible, has a well-defined function, and displays exquisite laminar specificity both in terms of receiving synapses in the retina and making them in a brain area called the optic tectum or superior colliculus. In work supported by this grant, we have identified several molecules likely to regulate laminar selectivity in retina, and now propose to investigate the ways in which they act. They include a set of four related synaptic proteins called Sidekick-1, Sidekick-2, Dscam and DscamL;a distant relative called JAM-B;and a remarkable family of ~60 closely related genes called protocadherins. In addition, we will study laminar targeting in tectum, so we can determine the relationship between lamina-specific choices made by dendrites and axons of single cells. Using these strategies we hope eventually to elucidate mechanisms that promote lamina- specific synapse formation and, by extension, defects in specificity that may underlie behavioral disorders.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS029169-22
Application #
8231533
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Talley, Edmund M
Project Start
1991-01-01
Project End
2013-02-28
Budget Start
2012-03-01
Budget End
2013-02-28
Support Year
22
Fiscal Year
2012
Total Cost
$536,107
Indirect Cost
$215,414
Name
Harvard University
Department
Microbiology/Immun/Virology
Type
Schools of Arts and Sciences
DUNS #
082359691
City
Cambridge
State
MA
Country
United States
Zip Code
02138
Duan, Xin; Krishnaswamy, Arjun; De la Huerta, Irina et al. (2014) Type II cadherins guide assembly of a direction-selective retinal circuit. Cell 158:793-807
Lilley, Brendan N; Krishnaswamy, Arjun; Wang, Zhi et al. (2014) SAD kinases control the maturation of nerve terminals in the mammalian peripheral and central nervous systems. Proc Natl Acad Sci U S A 111:1138-43
Hong, Y Kate; Park, SuHong; Litvina, Elizabeth Y et al. (2014) Refinement of the retinogeniculate synapse by bouton clustering. Neuron 84:332-9
Sümbül, Uygar; Song, Sen; McCulloch, Kyle et al. (2014) A genetic and computational approach to structurally classify neuronal types. Nat Commun 5:3512
Lilley, Brendan N; Pan, Y Albert; Sanes, Joshua R (2013) SAD kinases sculpt axonal arbors of sensory neurons through long- and short-term responses to neurotrophin signals. Neuron 79:39-53
Kay, Jeremy N; Chu, Monica W; Sanes, Joshua R (2012) MEGF10 and MEGF11 mediate homotypic interactions required for mosaic spacing of retinal neurons. Nature 483:465-9
Samuel, Melanie A; Zhang, Yifeng; Meister, Markus et al. (2011) Age-related alterations in neurons of the mouse retina. J Neurosci 31:16033-44
Kay, Jeremy N; Voinescu, P Emanuela; Chu, Monica W et al. (2011) Neurod6 expression defines new retinal amacrine cell subtypes and regulates their fate. Nat Neurosci 14:965-72
Hong, Y Kate; Kim, In-Jung; Sanes, Joshua R (2011) Stereotyped axonal arbors of retinal ganglion cell subsets in the mouse superior colliculus. J Comp Neurol 519:1691-711
Kay, Jeremy N; De la Huerta, Irina; Kim, In-Jung et al. (2011) Retinal ganglion cells with distinct directional preferences differ in molecular identity, structure, and central projections. J Neurosci 31:7753-62

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