Current understanding of the interactions between neurons, and between neurons and glia, required for the formation of neural circuits is incomplete. Fundamental gaps include identifying cell adhesion molecules that can generate the diversity needed to promote specific recognition between cells of the developing mammalian CNS, and elucidating associated signaling pathways that regulate several key steps, including elaboration of dendritic arbors and synaptogenesis. The long-term goal is to identify the molecular mechanisms that control the proper formation of neural circuits during development. The objective of this renewal application is to identify the molecular mechanisms by which the gamma-Pcdhs, a family of 22 cadherin superfamily adhesion molecules, regulate cortical dendrite arborization. The central hypothesis is that homophilic interactions between gamma-Pcdh tetramers on cortical neurons and astrocytes promote dendrite arborization by inhibiting a PKC signaling pathway. This hypothesis is based on extensive preliminary data generated by the applicant's laboratory during the prior funding period, and will be tested by pursuing 3 Specific Aims: 1) Determine the extent to which homophilic gamma -Pcdh interactions promote dendrite arborization in cortical neurons;2) Identify roles for astrocytic gamma -Pcdhs in cortica neuron dendrite arborization;and 3) Identify intracellular signaling mech- anisms regulating the gamma -Pcdhs'role in arborization.
Under Aim 1, a model resulting from preliminary in vitro assays--combinatorially diverse gamma -Pcdh cis-tetramers interact homophilically in trans--will be applied to cortical development. Neuronal gamma -Pcdh tetramer composition will be manipulated using transfection and several novel Pcdh- gamma knock-in transgenic mouse lines to directly address the role of interaction specificity in dendrite arborization.
Aim 2 build on preliminary data establishing astrocytic gamma -Pcdhs as key regulators of circuit form- ation in the spinal cord. Using astrocyte-restricted Cre transgenics with conditional Pcdh- gamma mutants and knock- ins in vivo, the role of astrocytic gamma -Pcdhs in dendrite arborization of cortical neurons will be delineated.
Aim 3 expands on preliminary data showing that a PKC signaling pathway is inhibited by the gamma -Pcdhs to promote dendrite arborization. A C-terminal residue shared by all gamma -Pcdhs has been identified that can be phosphorylated by PKC. We hypothesize that this disrupts the gamma -Pcdhs'ability to inhibit PKC signaling via inhibition of FAK, providing a signaling feedback mechanism. This will be tested using a series of point mutant and truncation Pcdh- gamma constructs in biochemical assays and neuronal cultures. The proposed research is significant, because it will identify molecular mechanisms that can account for diverse cell-cell interactions driving a key step in neural circuit formation, filling an important gap in current knowledge in the field. Such information will be critical to understanding, and eventually ameliorating, the many neurodevelopmental disorders that involve defective dendrite development and synaptogenesis.

Public Health Relevance

The proposed research is relevant to public health because it will identify molecular mechanisms that control neural circuit formation in the developing cerebral cortex, a process that goes awry in a plethora of impactful human disorders including autism spectrum disorders and intellectual disability. Identifying such mechanisms is a critical step towards understanding these disorders and, eventually, devising therapeutic approaches to their amelioration. Thus, the proposed research is relevant to the mission of NIH in that it will expand the neuroscience knowledge base towards the understanding of human disease and the processes of human development.

Agency
National Institute of Health (NIH)
Institute
National Institute of Neurological Disorders and Stroke (NINDS)
Type
Research Project (R01)
Project #
5R01NS055272-07
Application #
8703812
Study Section
Neurodifferentiation, Plasticity, and Regeneration Study Section (NDPR)
Program Officer
Talley, Edmund M
Project Start
2006-04-01
Project End
2017-05-31
Budget Start
2014-06-01
Budget End
2015-05-31
Support Year
7
Fiscal Year
2014
Total Cost
Indirect Cost
Name
University of Iowa
Department
Biology
Type
Schools of Arts and Sciences
DUNS #
City
Iowa City
State
IA
Country
United States
Zip Code
52242
Molumby, Michael J; Keeler, Austin B; Weiner, Joshua A (2016) Homophilic Protocadherin Cell-Cell Interactions Promote Dendrite Complexity. Cell Rep 15:1037-50
Bosch, Peter J; Fuller, Leah C; Sleeth, Carolyn M et al. (2016) Akirin2 is essential for the formation of the cerebral cortex. Neural Dev 11:21
Mah, Kar Men; Houston, Douglas W; Weiner, Joshua A (2016) The γ-Protocadherin-C3 isoform inhibits canonical Wnt signalling by binding to and stabilizing Axin1 at the membrane. Sci Rep 6:31665
Keeler, Austin B; Molumby, Michael J; Weiner, Joshua A (2015) Protocadherins branch out: Multiple roles in dendrite development. Cell Adh Migr 9:214-26
Keeler, Austin B; Schreiner, Dietmar; Weiner, Joshua A (2015) Protein Kinase C Phosphorylation of a γ-Protocadherin C-terminal Lipid Binding Domain Regulates Focal Adhesion Kinase Inhibition and Dendrite Arborization. J Biol Chem 290:20674-86
Blumberg, Mark S; Coleman, Cassandra M; Sokoloff, Greta et al. (2015) Development of twitching in sleeping infant mice depends on sensory experience. Curr Biol 25:656-62
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Garrett, Andrew M; Schreiner, Dietmar; Lobas, Mark A et al. (2012) ýý-protocadherins control cortical dendrite arborization by regulating the activity of a FAK/PKC/MARCKS signaling pathway. Neuron 74:269-76
Schreiner, Dietmar; Weiner, Joshua A (2010) Combinatorial homophilic interaction between gamma-protocadherin multimers greatly expands the molecular diversity of cell adhesion. Proc Natl Acad Sci U S A 107:14893-8
Garrett, Andrew M; Weiner, Joshua A (2009) Control of CNS synapse development by {gamma}-protocadherin-mediated astrocyte-neuron contact. J Neurosci 29:11723-31

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