To Pinpoint the Location and the Orientation of Proteins Associated with Dense-Core Vesicles (DCVs) using CLEM

Abstract

Exocytosis of catecholamine (adrenaline and noradrenaline) from adrenal chromaffin cells is important for stress responses and insulin release from pancreatic beta cells is critical in regulating blood glucose levels. These exocytic processes are highly regulated by a dozens of key proteins in eukaryotic cells. While the origin, transport, and delivery of cargo-loaded vesicles (dense-core vesicles) and the proteins involved is well studied, how these proteins are organized with respect to dense-core vesicles (DCVs) at the nanoscale remains to be explored. Here, we directly image several proteins that are key regulators of the transport, docking, and priming of DCVs at the plasma membrane. Specifically, correlative super-resolution (dSTORM) light and platinum replica transmission electron microscopy (CLEM) imaging was performed on PC12 cells (a rat adrenal chromaffin-derived neuroendocrine cell line) that were transfected with proteins of interest. We aligned super-resolution dSTORM images of Rab proteins (Rab27a and Rab3a) and Rab effector proteins (granuphilin and Rabphilin) with corresponding TEM images of the plasma membrane and observed the precise correlation between proteins and vesicles at the plasma membrane. The nano-scale molecular architecture of DCVs generated from this correlative imaging will help us understand how key proteins guide the docking, priming, and fusion of DCVs in endocrine cells.