A quantitative analysis of the molecular organization of dendritic spines from hippocampal neurons
by Martin Sebastian Helm
Date of Examination:2019-03-26
Date of issue:2019-08-20
Advisor:Prof. Dr. Silvio O. Rizzoli
Referee:Prof. Dr. Silvio O. Rizzoli
Referee:Prof. Dr. Nils Brose
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Abstract
English
Dendritic spines are the major excitatory postsynaptic compartment in the brain. Despite its essential function in synaptic transmission and plasticity, we are still lacking a comprehensive and quantitative understanding of its molecular composition. However, this knowledge is crucial to appreciate the minute regulatory details that affect learning and memory. Here, I investigated the molecular architecture of dendritic spines in absolute quantitative terms and on the nanoscale. I report the localization and abundance of 105 postsynaptic proteins, differentiating between spine classes. Surprisingly, the investigated spine types show highly similar morphology as well as molecular composition. I found that proteins belonging of the same pathway do localize with each other and that their abundance is equally correlated. Using pharmacological treatment, I also show that the organization of dendritic spines is relatively stable during homeostatic plasticity, with only minor changes. Interestingly, the copy number of a given protein on the postsynapse correlated with its copy number in the presynapse, corroborating a tight link between both compartments. In addition, I report the neuronal proteome of pure hippocampal excitatory neurons in absolute values. This revealed that the abundance of a protein decreases with its size, probably because larger proteins do attract damage faster, or because it is energetically costly to produce large proteins. Also, the copy number distribution of mitochondria is highly different to all other investigated compartments, most likely due to its highly specialized function and prokaryotic origin. In total, the database I provide is the most extensive quantitative description of dendritic spines to date. It provides the foundation for highly detailed in silico modelling approaches and will be an important reference tool for synaptic function.
Keywords: dendritic spine; postsynaptic density; super-resolution microscopy; quantitative biochemistry; modelling