"Light" and "dark" pinealocytes of the porcine pineal gland.
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Abstract:
Both qualitative and quantitative comparative studies of "dark" and "light" pinealocytes of the porcine pineal gland have been carried out. These cells differ from each other in their electronic density of cytoplasm, shape of nucleus, the structure of membrane bound dense bodies and the number of microtubules and smooth endoplasmic reticulum. The membrane bound dense bodies--characteristic structures of pig pinealocytes as well dense core vesicles occur in both types of cells. The relative volume of the majority of the cells' organellae apart from the Golgi apparatus, also do not show any significant difference. The results obtained support a functional basis for pinealocyte differentiation in the porcine pineal gland.Keywords:
Pinealocyte
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Pars intermedia
Cell type
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Pinealocyte
Gerbil
Secretory Vesicle
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Pinealocyte morphology reveals cells which appear to be specialized for endocrine secretion. Abundant, rough and smooth endoplasmic reticulum, as well as free ribosomes and dense-cored vesicles manufactured by active Golgi complexes, predict the production of proteina-ceous and other compounds. The innervation of the pineal of vertebrates including mammals has been reviewed recently by J. A. Kappers. It is known that in mammals there is a rich pinealopetal ortho-sympathetic innervation by nerves originating in the superior cervical ganglion and reaching the gland via the nervii conarii. In certain mammals, including the rabbit, hamster, and mouse, dense-cored or granulated vesicles migrate to the end of long pinealocyte processes where secretory products appear to be delivered to the pericapillary spaces and intercellular spaces. Pevet, dense-cored or granulated vesicle formation by Golgi saccules has been observed in the pinealocytes of most mammals, and the rate of their formation is dependent on different physiological conditions.
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Sigmodon hispidus
Pinealocyte
Organelle
Parenchyma
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Both qualitative and quantitative comparative studies of "dark" and "light" pinealocytes of the porcine pineal gland have been carried out. These cells differ from each other in their electronic density of cytoplasm, shape of nucleus, the structure of membrane bound dense bodies and the number of microtubules and smooth endoplasmic reticulum. The membrane bound dense bodies--characteristic structures of pig pinealocytes as well dense core vesicles occur in both types of cells. The relative volume of the majority of the cells' organellae apart from the Golgi apparatus, also do not show any significant difference. The results obtained support a functional basis for pinealocyte differentiation in the porcine pineal gland.
Pinealocyte
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Morphometric analysis of the superficial pineal gland of intact and blinded golden hamsters was conducted at both the light and electron microscopic level. The volume of the superficial gland was estimated to be 151 X 10(6) micron 3, comprising 90-94% of the total pineal parenchymal tissue. Analysis of structural rhythms in animals maintained under a 14:10 L:D cycle showed significant 24-hr variations in values for pinealocyte nuclei, nucleoli, rough and smooth endoplasmic reticulum, Golgi bodies, dense bodies, and dense-cored vesicles. Peak values for these structures generally occurred at the light:dark interface. These results provide morphological correlates for known rhythmic variations in the synthesis of pineal-gland products. Superficial pineals examined 8 weeks following optic enucleation exhibited a decrease in the volume of pinealocyte nuclei and cytoplasm, while nucleolar size and the amounts of smooth and rough endoplasmic reticulum, Golgi bodies, dense bodies and dense-cored vesicles were enhanced. The latter changes are interpreted as indications of increased synthetic activity by the superficial pineal gland in response to light deprivation.
Pinealocyte
Lipid droplet
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ABSTRACT Alterations which occur during differentiation in the fine structure of the cement gland of the embryo of Xenopus laevis have been investigated. The organ anlage at the late neurula stage is composed of cuboidal cells of comparatively simple cytoplasmic structure. Coincident with the subsequent cellular elongation there is a formation of extensive arrays of functionally interrelated membrane systems, leading to the production of a mucin-like secretory substance. Although there is no direct structural continuity between the membranes of the endoplasmic reticulum and the Golgi apparatus, small vesicles which seem to originate from areas of agranular reticulum appear to transport material synthesized in the endoplasmic reticulum to the Golgi zone. Further elaboration of the product at the site of the Golgi material is suggested by the progressive increase in the quantity of the contents as the cisternae enlarge to form secretory granules. Other notable features of the differentiating cells are microtubules and cytoplasmic filaments, many of which are oriented in the direction of cellular elongation. In suitably preserved specimens, large numbers of glycogen granules are present. The degenerating gland is characterized by the appearance of large autolytic vacuoles within the cytoplasm. Traces of the membrane systems are present and, in many cells, there remain large numbers of secretory granules.
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ABSTRACT Human cytomegalovirus (HCMV) induces profound changes in infected cell morphology, including a large cytoplasmic inclusion that corresponds to the virion assembly complex (AC). In electron micrographs, the AC is a highly vacuolated part of the cytoplasm. Markers of cellular secretory organelles have been visualized at the outer edge of the AC, and we recently showed that a marker for early endosomes (i.e., early endosome antigen 1) localizes to the center of the AC. Here, we examined the relationship between the AC and components of the secretory apparatus, studied temporal aspects of the dramatic infection-induced cytoplasmic remodeling, examined the three-dimensional structure of the AC, and considered the implications of our observations for models of HCMV virion maturation and egress. We made three major observations. First, in addition to being relocated, the expression levels of some organelle markers change markedly during the period while the AC is developing. Second, based on three-dimensional reconstructions from z-series confocal microscopic images, the observed concentric rings of vesicles derived from the several compartments (Golgi bodies, the trans -Golgi network [TGN], and early endosomes) are arranged as nested cylinders of organelle-specific vesicles. Third, the membrane protein biosynthetic and exocytic pathways from the endoplasmic reticulum to the Golgi bodies, TGN, and early endosomes are in an unusual arrangement that nonetheless allows for a conventional order of biosynthesis and transport. Our model of AC structure suggests a mechanism by which the virus can regulate the order of tegument assembly.
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Secretory Vesicle
Brefeldin A
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The yeast Sec23 protein is required in vivo and in vitro for transport of proteins from the endoplasmic reticulum (ER) to the Golgi apparatus. Ultrastructural localization of the Sec23p mammalian homologue (detected by antibody cross-reaction) in exocrine and endocrine pancreatic cells shows a specific distribution to the cytoplasmic zone between the transitional ER cisternae and Golgi apparatus where it appears associated with the tubular protuberances of the transitional ER cisternae, as well as with a population of vesicles, and surrounding cytoplasm. When ER-Golgi transport is interrupted with an energy poison, protuberances and transfer vesicles markedly decrease but Sec23p immunoreactive sites remain in the transitional cytoplasm not apparently tethered by membrane attachment. This unanticipated degree of organization suggests that cytosolic proteins, such as Sec23p, may be retained in specialized areas of the cytoplasm. A structure within the transitional zone may organize the flux of transport vesicles and Sec proteins so as to ensure efficient protein traffic in this limb of the secretory pathway.
COPI
Secretory protein
Transport protein
COPII
Secretory Vesicle
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