Compartmentalization of Pancreatic Secretory Zymogen Granules as Revealed by Low-Voltage Transmission Electron Microscopy

Abstract

SummaryLow-voltage (5-kV) transmission electron microscopy revealed a novel aspect of the pancreatic acinar cell secretory granules not previously detected by conventional (80-kV) transmission electron microscopy. Examination of ultra-thin (30-nm) sections of non-osmicated, stain-free pancreatic tissue sections by low-voltage electron microscopy revealed the existence of granules with non-homogeneous matrix and sub-compartments having circular or oval profiles of different electron densities and sizes. Such partition is completely masked when observing tissues after postfixation with osmium tetroxide by low-voltage transmission electron microscopy at 5 kV and/or when thicker sections (70 nm) are examined at 80 kV. This morphological partition reflects an internal compartmentalization of the granule content that was previously predicted by morphological, physiological, and biochemical means. It corresponds to the segregation of the different secretory proteins inside the granule as demonstrated by high-resolution immunocytochemistry and reflects a well-organized aggregation of the secretory proteins at the time of granule formation in the trans-Golgi. Such partition of the granule matrix undergoes changes under experimental conditions known to alter the secretory process such as stimulation of secretion or diabetes. (J Histochem Cytochem 59:899-907, 2011)

MAPK Signaling Is Required for Dedifferentiation of Acinar Cells and Development of Pancreatic Intraepithelial Neoplasia in Mice

“…Normal acinar cells have 2 very distinct features when observed under transmission electron microscopy; first, the nucleus is round and located basally, and, second, the cytoplasm is filled with large zymogen granules. 26,27 In contrast, PanIN cells had few small zymogen granules in their cytoplasm, highly atypical nuclei, and microvilli on their luminal edge (Figure 5 A , bottom row). At 1.5 days of MEK1/2 inhibition, we observed rare cells presenting with an increased number of zymogen granules (Figure 5 B , bottom row).…”

In vitro secretion of zymogens by bovine pancreatic acini and ultra-structural analysis of exocytosis

“…Examination of cells at high magnification employing electron microscopy as a tool had a remarkable impact on cell biology [33] , as this examination aids in visualizing both the surface and ultra-structure of the cells. The secretory granule is spherical and surrounded by an intact, thick bi-layered membrane when the ultra-structure is visualized under TEM.…”

Perspectives on low voltage transmission electron microscopy as applied to cell biology

“…In what concern the pancreatic secretory granules, we revealed the presence of a partition within its matrix. This partition pattern appears to be specific to the granules of the pancreatic acinar cells since secretory granules of endocrine islet cells within the same tissue sections or granules of other endocrine glands prepared according to the same protocol, do not display such patterns when examined by LVTEM (Bendayan et al, ). On the other hand, when osmicated pancreatic tissue is examined by low voltage, the granules appeared very dense without any internal substructure; they appear however delineated by a well defined membrane (Fig.…”

“…In recent years transmission electron microscope operating at 5 kV accelerating voltage (Delong et al, ), was employed for analysis of polymer‐based materials and the benefit of increased image contrast in organic materials analyzed by low voltage TEM was demonstrated (Drummy et al, ). We have recently modified tissue preparation procedures to enable the use of low voltage transmission electron microscopy (LVTEM) in cell biology (Bendayan et al, ). Modifications consist in eliminating the use of heavy metals in the fixation and counterstaining steps and in preparing ultra‐thin tissue sections not thicker than 40 nm.…”

“…In previous studies we reported results pertaining to secretory granules of the pancreatic cells. LVTEM allowed revealing substructures in the granules reflecting their internal compartmentalization (Bendayan et al, ). These observations reinforced previous predictions as well as biochemical, physiological, and morphological data, indicating that indeed the content of the granules is expected to be segregated (Gingras and Bendayan, ).…”