Abstract
Subcellular neighborhoods, comprising specific ratios of organelles and proteins, serve a multitude of biological functions and are of particular importance in secretory cells. However, the role of subcellular neighborhoods in insulin vesicle maturation is poorly understood. Here, we present single-cell multiple distinct tomogram acquisitions of β cells for in situ visualization of distinct subcellular neighborhoods that are involved in the insulin vesicle secretory pathway. We propose that these neighborhoods play an essential role in the specific function of cellular material. In the regions where we observed insulin vesicles, a measurable increase in both the fraction of cellular volume occupied by vesicles and the average size (diameter) of the vesicles was apparent as sampling moved from the area near the nucleus toward the plasma membrane. These findings describe the important role of the nanometer-scale organization of subcellular neighborhoods on insulin vesicle maturation.
Highlights
Subcellular neighborhoods consist of groupings of specialized organelles and proteins that have one or more specific jobs to perform in the cell
To eliminate bias in future studies, regions/neighborhoods would be more appropriately sampled either randomly or systematically for more meaningful interpretation with better statistical representation and biological meaning. Combining with another whole-cell imaging method, soft x-ray tomography, can give us much better and comprehensive knowledge about the cellular architecture of the whole-cell [28]. These manually selected regions illustrate insulin vesicle maturation and trafficking in situ to serve as a pilot study toward deeper statistical analysis
We found that vesicles are larger, are packed more closely, and develop increasingly electron-dense crystalline cores as they move within the cell from the trans-Golgi to the plasma membrane (PM)
Summary
Subcellular neighborhoods consist of groupings of specialized organelles and proteins that have one or more specific jobs to perform in the cell. The temporal and spatial distribution of these neighborhoods is essential for a multitude of biological functions, including protein production, maturation, and transport [1]. Insulin is a peptide hormone produced by pancreatic cells that is released when blood glucose levels rise [2]. Insulin vesicle production and properly timed secretion are the most critical functions of cells, with loss or misregulation leading to diabetes mellitus [3, 4]. Glucose-induced insulin secretion is a complex process that requires the endoplasmic reticulum (ER), Golgi, mitochondrial, cytoskeletal, and membrane fusion machinery work synergistically. Fundamental questions remain about how these different components act together to orchestrate insulin secretion
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