Details

Autor(en) / Beteiligte

• Marrs, Glen Stanley

Titel

Developmental morphogenesis of PSD-95 containing synapses at dendritic spines and β-integrin dependent dendrite stabilization

Ort / Verlag

ProQuest Dissertations & Theses

Erscheinungsjahr

2005

Quelle

ProQuest Dissertations & Theses A&I

Beschreibungen/Notizen

• Neural communication and CNS function depends upon the proper developmental organization between synapses and their principal structural components. My investigations examined the formation and stabilization of excitatory synapses as well as dendritic structures that bear these synapses, specifically: the relation of developing excitatory postsynaptic structures to dendritic spines, factors regulating the formation and patterning of postsynaptic structures, and the adhesive stability of dendritic arbors. To study the development of postsynaptic densities (PSDs) in relation to dendritic spine formation, I utilized live confocal time-lapse imaging to record dynamic motility of a GFP fusion protein containing PSD95. PSDs were selectively associated with more stable dendritic spines, but were highly dynamic and mobile within semi-stable spine precursors. Formation of new PSDs occurred following stabilization of filopodial precursors to dendritic spines. PSD clusters were highly co-localized with presynaptic protein markers, suggesting that most fluorescent PSDs represent functional synaptic sites. These results support a model whereby synapses form concurrent with dendritic spine stabilization, and further indicate that developing synapses are highly dynamic structures. I next examined factors that potentially regulate the formation and patterning of PSDs and synapses. Specifically, I addressed whether glutamate neurotransmission was necessary for regulating the formation and spatial organization of PSDs at the hippocampal giant Mossy Fiber (MF) synapse. Chronic blockade of ionotropic or metabotropic glutamate receptors did not alter the spatial distribution or clustering of PSDs at MF synapses. These results indicate that assembly of the core PSD and patterning in the MF system occurs independently of glutamate neurotransmission. Finally, I examined what adhesive molecules participate in the maintenance of dendritic structure. Fluorescently labeled chick retinal ganglion cells (RGCs) were examined following disruption of adhesion complexes using highly target specific cell permeable peptides. Dendritic arbors appeared intact following inhibition of N-cadherin adhesion, but were retracted following disruption of β1-integrin adhesion. Furthermore, a peptide that disrupts β1-integrin adhesion (by initiating translocation of Fer tyrosine kinase from the N-cadherin complex) also resulted in RGC dendritic collapse. These results support a role for integrins in RGC dendritic stability, with classic cadherins potentially regulating dendrite maintenance through a β-catenin independent integrin signaling pathway.