Forum 10/05/2006

“Multi-resolution 3D Structure Studies of the Insulin-Secreting Pancreatic Beta Cell by Cellular Tomography”

Brad J. Marsh – Institute for Molecular Bioscience, Centre for Microscopy & Microanalysis, and School of Molecular & Microbial Sciences, The University of Queensland, Brisbane, Australia

The beta cells of the endocrine pancreas are the sole source of insulin in mammals.  Death of the beta cells, or their abnormal processing/trafficking/secretion of insulin results in the disease known as Diabetes.  We are focused on understanding these basic mechanisms from a structural cell biology perspective, so that we can identify how and where defects in these steps occur.  By necessity, this work has led us to develop techniques for the improved preservation and imaging of pancreatic beta cells in situ within “pancreatic islets” isolated from mice and humans.  This technology combines methods for preserving the physiological state/architecture of the beta cell as reliably as possible by ultra-rapid freezing/freeze-substitution with the technique of electron microscope (EM) tomography.

Images from thick slices cut from such cells tilted at many different angles in the EM are used to generate high resolution 3D reconstructions of large cellular volumes.  Cell tomograms generated in this way have already provided new insight into structure-function relationships among organelles of the insulin biosynthetic pathway and revealed novel connections between compartments that are normally spatially/functionally distinct. To complement our move toward true high-throughput cellular tomography, we have undertaken to reconstruct an entire mammalian (beta) cell in 3D at ≤5nm resolution.  This work requires the parallel development and implementation of new mathematical tools for extracting useful structural/biological information from the data in a rapid, reliable and quantifiable manner.  Such a “Visible Cell” atlas will provide a unique structural framework which should serve as a major informatics/3D visualization/educational resource for the molecular cell biology, Diabetes and computational simulation communities at both the national and international levels.

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