Reconstructing neural circuits using multiresolution correlated light and electron microscopy.

Correlated light and electron microscopy (CLEM) can be used to combine functional and molecular characterizations of neurons with detailed anatomical maps of their synaptic organization. Here we describe a multiresolution approach to CLEM (mrCLEM) that efficiently targets electron microscopy (EM) imaging to optically characterized cells while maintaining optimal tissue preparation for high-throughput EM reconstruction. This approach hinges on the ease with which arrays of sections collected on a solid substrate can be repeatedly imaged at different scales using scanning electron microscopy. We match this multiresolution EM imaging with multiresolution confocal mapping of the aldehyde-fixed tissue. Features visible in lower resolution EM correspond well to features visible in densely labeled optical maps of fixed tissue. Iterative feature matching, starting with gross anatomical correspondences and ending with subcellular structure, can then be used to target high-resolution EM image acquisition and annotation to cells of interest. To demonstrate this technique and range of images used to link live optical imaging to EM reconstructions, we provide a walkthrough of a mouse retinal light to EM experiment as well as some examples from mouse brain slices.

Alteration in synaptic nanoscale organization dictates amyloidogenic processing in Alzheimer's disease.

Despite intuitive insights into differential proteolysis of amyloid precursor protein (APP), the stochasticity behind local product formation through amyloidogenic pathway at individual synapses remain unclear. Here, we show that the major components of amyloidogenic machinery namely, APP and secretases are discretely organized into nanodomains of high local concentration compared to their immediate environment in functional zones of the synapse. Additionally, with the aid of multiple models of Alzheimer's disease (AD), we confirm that this discrete nanoscale chemical map of amyloidogenic machinery is altered at excitatory synapses. Furthermore, we provide realistic models of amyloidogenic processing in unitary vesicles originating from the endocytic zone of excitatory synapses. Thus, we show how an alteration in the stochasticity of synaptic nanoscale organization contributes to the dynamic range of C-terminal fragments ß (CTFß) production, defining the heterogeneity of amyloidogenic processing at individual synapses, leading to long-term synaptic deficits as seen in AD.

Real-time nanoscale organization of amyloid precursor protein.

Despite an intuitive understanding of the role of APP in health and disease, there exist few attempts to dissect its molecular localization at excitatory synapses. Though the biochemistry involved in the enzymatic processing of APP is well understood, there is a void in understanding the nonuniformity of the product formation in vivo. Here, we employed multiple paradigms of single molecules and ensemble based nanoscopic imaging to reveal that APP molecules are organized into regulatory nanodomains that are differentially compartmentalized in the functional zones of an excitatory synapse. Furthermore, with the aid of high density single particle tracking, we show that the lateral diffusion of APP in live cells dictates an equilibrium between these nanodomains and their nano-environment, which is affected in a detrimental variant of APP. Additionally, we incorporate this spatio-temporal detail 'in silico' to generate a realistic nanoscale topography of APP in dendrites and synapses. This approach uncovers a nanoscale heterogeneity in the molecular organization of APP, depicting a locus for differential APP processing. This holistic paradigm, to decipher the real-time heterogeneity of the substrate molecules on the nanoscale, could enable us to better evaluate the molecular constraints overcoming the ensemble approaches used traditionally to understand the kinetics of product formation.