A transplantable acinar cell tumor of the rat pancreas has been examined by light and electron microscopy. The tumor cells, though highly cytodifferentiated and characterized by the presence of abundant rough-surfaced endoplasmic reticulum, elements of the Golgi complex, and zymogen granules, undergo mitosis in a manner similar to that seen in the developing pancreas. Cells in the parenchyma of the tumor grow as disarrayed cords and sheets, are randomly oriented with respect to each other, and do not form acinar structures. However, when in contact with the adventitial surface of blood vessels, the tumor cells palisade and form a polarized layer of cells with their zymogen granule-rich poles oriented away from the vessel lumen. Only in this area of the tumor is a basal lamina present that underlies the basal plasmalemma of the reoriented epithelial cells. Freeze-fracture electron microscopy of tumor cells in the parenchyma shows extensive disruption of tight junctions whose sealing strands are randomly distributed over the entire plasmalemma. Gap junctions are infrequent and when present are often enclosed by tight-junctional strands. Intramembrane particles are randomly distributed over the cell surface. Both the absence of basal lamina and derangement of the junctional complexes may account in part for the altered morphogenesis of this tumor.The pancreatic acinar cell has for many years been used in the study of the biosynthesis, packaging, and discharge of secretory proteins. Though many of the steps leading to the discharge of digestive enzymes and proenzymes have been identified (1, 2), the details of controls involved in the release mechanism are still obscure.The role of tissue organization and its influence upon cell function has been under consideration in our laboratory (3-5). One approach to this problem has been to examine the developing rat pancreas in an attempt to correlate the concomitant events of histogenesis and cytodifferentiation with secretagogue response (6). In this paper we characterize morphologically a pancreatic acinar cell tumor, first described by Reddy and Rao (7, 8), that shows a high level of cytodifferentiation without organization into acinar structures. This system, therefore, provides an opportunity to study the relationship between epithelial organization and the stimulated release of secretory proteins. We report here on the morphologic features of the tumor obtained from passages 14 through 20 using light and electron microscopy and freeze-fracture techniques. With this morphotogic baseline, we describe in the subsequent papers of this series the functional and biochemical properties of the tumor cells. Portions of this study have been published in abstract form (9). MATERIALS AND METHODS Tumor TransplantationFischer 344 Sprague-Dawley rats bearing tumors in the tenth passage were the generous gift of Drs. J. K. Reddy and M. S. Rao of Northwestern University. The tumors were passaged in weanling Sprague-Dawley Fischer 344 rats (HarlanSprague Dawley, Madison, Wl) a...
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.