Protein-accumulating cells and dilated cisternae of the endoplasmic reticulum in three glucosinolate-containing genera: Armoracia,Capparis, Drypetes

Three glucosinolate-containing species, Armoracia rusticana Gaertner, Meyer et Scherbius (Brassicaceae), Capparis cynophallophora L. (Capparaceae) and Drypetes roxburghii (Wall.) Hurusawa (Euphorbiaceae), are shown by both light and electron microscopy to contain protein-accumulating cells (PAC). The PAC of Armoracia and Copparis (former myrosin cells) occur as idioblasts. The PAC of Drypetes are usual members among axial phloem parenchyma cells rather than idioblasts. In Drypetes the vacuoles of the PAC are shown ultrastructurally to contain finely fibrillar material and to originate from local dilatations of the endoplasmic reticulum. The vacuoles in PAC of Armoracia and Capparis seem to originate in the same way; but ultrastructurally, their content is finely granular. In addition, Armoracia and Capparis are shown by both light and electron microscopy to contain dilated cisternae (DC) of the endoplasmic reticulum in normal parenchyma cells, in accord with previous findings for several species within Brassicaceae. The relationship of PAC and DC to glucosinolates and the enzyme myrosinase is discussed.Abbreviations ABB aniline blue black - DC dilated cisternae - EM electron microscopy - ER endoplasmic reticulum - GMA glycolmethacrylate - LM light microscopy - MBB mercuric bromphenol blue - PAC protein-accumulating cells - PAS periodic acid-Schiff Recipient of an Alexander von Humboldt Award and in residence at the University of Heidelberg during the period when this research was carried out. Permanent address: Department of Botany and Cell Research Institute, University of Texas, Austin, Texas 78712, USA     

Rod-shaped accumulations in cisternae of the endoplasmic reticulum in root cells of Lepidium sativum seedlings

Summary Ultrathin sections through the median plane of norm al, 48-hrs-old seedling roots of cress, showed the presence of accumulations of a finely fibrillar material. These inclusions were confined to the cisternae of the granular endoplasmic reticulum of surface cell layers of the root tip and the root-hair zone. The rod-shaped structure and random orientation of these inclusions were clearly seen in 3-dimensional reconstructions of serial ultrathin sections.     

The morphology,occurrence, and distribution of dilated cisternae of the endoplasmic reticulum in tissues of plants of theCruciferae

Summary Morphology, occurrence, and distribution of dilated cisternae of the endoplasmic reticulum (ER) were studied by electron microscopy. The cisternae which contained an electron-dense matrix were intimately associated with the granular ER membranes appearing as tubular necks at the edges of the ER profiles. After budding off from the ER the cisternae still had ribosomes attached to the outside of the bounding membranes. The accumulations were variable in shape, being 0.4 to 1.5 in width and 4 to 5 in length.The cisternae were found to be unique for plants of theCruciferae and could not be observed in species from related families such asPapaveraceae andResedaceae.The dilated cisternae were a common component of the cytoplasm in root tips, stems, and leaves. In meristematic cells the number of accumulations was small but increased in older differentiating cells of the root cap. The similarity to microbodies described by previous authors from other plants is discussed.     

Membrane associations between subsurface cisternae of endoplasmic reticulum and the plasma membrane of rat Sertoli cells

Close membrane associations between the endoplasmic reticulum and the plasma membrane (ER-PM) occur in specialized regions of the rat Sertoli cell cytoplasm. They are characterized, in freeze fracture replicas, as mesa-like modifications of E membrane fracture faces or as corresponding discoid depressions on P membrane fracture faces. When these structures lie along transitional regions in the membrane fracture plane, they are seen to be complementary, and the space between them to be greatly reduced. These specialized close membrane associations may represent adhesive sites between the endoplasmic reticulum and the plasma membrane. However, their resemblance to vascular endothelial fenestrae which are known to be sites of increased membrane permeability may suggest other functional roles.     

Paired cisternae of endoplasmic reticulum in developing ovarian oocytes of the golden hamster

Paired cisternae of rough endoplasmic reticulum linked together by two parallel structures exhibiting periodic striations have been observed in the cytoplasm of small pre-antrum oocytes in the golden hamster. They are present only in oocytes from animals older than 3 weeks of age. Two or more such pairs may be associated with one another, and similar structures have been observed in contact with the nuclear envelope. The peak incidence of the paired membranes coincides with a sharp increase in rough endoplasmic reticulum as the oocyte commences rapid growth. A suggested role for the paired membranes in production of new endoplasmic reticulum is discussed.     

Collagen lysyl hydroxylation occurs within the cisternae of the rough endoplasmic reticulum.

Resolution of the heavy microsomal fraction of lung tissue by Ficoll density gradient centrifugation yielded a rough endoplasmic reticulum microsomal fraction containing the highest specific activity of detergent-released lysyl hydroxylase. This same microsomal fraction was previously shown to contain the highest specific activity of detergent-released prolyl hydroxylase activity. When hydroxylation was inhibited during the biosynthesis of collagen, this microsomal fraction contained lysine-rich, hydroxylysine-deficient, collagenase-digestible substrate that could be hydroxylated in the absence of detergent. The results indicate coordinate localization of both prolyl and lysyl hydroxylation reactions within the cisternae of the rough endoplasmic reticulum.     

Laminated cisternae of the rough endoplasmic reticulum induced by coronavirus MHV-A59 infection

The infection of murine fibroblasts of the sac- line with a coronavirus, mouse hepatitis virus strain A59 (MHV-A59), results in a novel modification to some cisternae of the rough endoplasmic reticulum (RER). From 8 hours post infection (h.p.i.) we see in thin sections pairs of cisternae closely, stably and uniformly aligned. Serial sectioning shows that the regions of pairing or lamination extend for many thousands of nm in two dimensions, with the spacing between the juxtaposed membranes remaining very uniform at about 18 nm. These structures appear coincident with the onset of accumulation of the viral glycoprotein E1 in the RER membrane but 2 hours after the viral glycoprotein E2 can first be detected there. Ribosomes are excluded from the paired cisternal surfaces, while budding of progeny virions has never been seen at the cisternal membranes facing the cytosol, although ribosomes bind there. The lumina of paired cixternae are usually devoid of virions which, however, accumulate in areas where the paired cisternae diverge. Electron immunocytochemistry shows that both E1 and E2 glycoproteins are abundant in the paired cisternae. Following labelling for the E1 glycoprotein we see a periodic fine structure, rows of "beads" with a centre to centre spacing of about 7.5 nm, in the region between the paired membranes. In oblique sections of this region in cells fixed as if for the immunoperoxidase labelling, but omitting all its steps we see parallel rows of "beads" separated by about 7 nm. We suggest that the membrane spanning viral glycoprotein E1 together with viral nucleocapsids may be involved in laminating cisternae of the RER.     

Dilated cisternae of nuclear envelope and rough endoplasmic reticulum in the proventriculus of Drosophila auraria larvae

In the cells of the middle layer of the proventriculus of Drosophila auraria larvae, the nuclear envelope and the rough endoplasmic reticulum are always found in the form of dilated cisternae. The length of these cisternae can reach 10 mu. There are indications that materials from the outer membrane of the nuclear envelope are directly transported to the Golgi complex of the examined cells.     

Mechanism of collapse of endoplasmic reticulum cisternae during African swine fever virus infection

Infection of cells with African swine fever virus (ASFV) can lead to the formation of zipper-like stacks of structural proteins attached to collapsed endoplasmic reticulum (ER) cisternae. We show that the collapse of ER cisternae observed during ASFV infection is dependent on the viral envelope protein, J13Lp. Expression of J13Lp alone in cells is sufficient to induce collapsed ER cisternae. Collapse was dependent on a cysteine residue in the N-terminal domain of J13Lp exposed to the ER lumen. Luminal collapse was also dependent on the expression of J13Lp within stacks of ER where antiparallel interactions between the cytoplasmic domains of J13Lp orientated N-terminal domains across ER cisternae. Cisternal collapse was then driven by disulphide bonds between N-terminal domains arranged in antiparallel arrays across the ER lumen. This provides a novel mechanism for biogenesis of modified stacks of ER present in cells infected with ASFV, and may also be relevant to cellular processes.     

The endoplasmic reticulum in regenerating liver cells

Summary Light-microscopic analysis of mouse liver homogenates six days after partial hepatectomy, showed a higher percentage of nuclei with adherent cytoplasm than homogenates from normal liver. This observation was true for animals with either a slow or rapid recovery of body weight after the operation. The phenomenon was not a function of the changes in the proportions of parenchymal and non-parenchymal tissue in the regenerating liver.Electron-microscopic analysis of random samples from normal and regenerating livers indicated an increase in the perinuclear rough endoplasmic reticulum, and a displacefment of the glycogen depots within the regenerating cells six days after partial hepatectomy.The marked resistance towards homogenization, shown by the cytoplasm of the regenerating cells, may have been due to the observed increase of perinuclear membranes. However, qualitative changes of the cell membranes and a general decrease of proteolytic activity connected with liver regeneration may also have contributed.     

Dispersion of cisternae of rough endoplasmic reticulum in aging CNS neurons: a strictly linear trend.

Dispersion of cisternae of rough endoplasmic reticulum (RER) in aging rats has been determined quantitatively for mitral cells of the olfactory bulb and Purkinje cells of the cerebellum using a recently published morphometric technique (Cruz Orive, '76). In both cell types dispersion of cisternae occurred throughout the period studied and in a linear fashion. The observed RER dispersion cannot be attributed to a decrease in the total amount of RER, since the total amount of RER was constant in Purkinje cells and increased in mitral cells during the age studied.     

Sulfatase modifying factor 1 trafficking through the cells: from endoplasmic reticulum to the endoplasmic reticulum

Sulfatase modifying factor 1 (SUMF1) is the gene mutated in multiple sulfatase deficiency (MSD) that encodes the formylglycine-generating enzyme, an essential activator of all the sulfatases. SUMF1 is a glycosylated enzyme that is resident in the endoplasmic reticulum (ER), although it is also secreted. Here, we demonstrate that upon secretion, SUMF1 can be taken up from the medium by several cell lines. Furthermore, the in vivo engineering of mice liver to produce SUMF1 shows its secretion into the blood serum and its uptake into different tissues. Additionally, we show that non-glycosylated forms of SUMF1 can still be secreted, while only the glycosylated SUMF1 enters cells, via a receptor-mediated mechanism. Surprisingly, following its uptake, SUMF1 shuttles from the plasma membrane to the ER, a route that has to date only been well characterized for some of the toxins. Remarkably, once taken up and relocalized into the ER, SUMF1 is still active, enhancing the sulfatase activities in both cultured cells and mice tissues.     

Dynamic behavior of endoplasmic reticulum in living cells

Endoplasmic reticulum (ER) was studied by fluorescence microscopy of living CV-1 cells treated with the fluorescent carbocyanine dye DiOC6(3). Using video recording and image processing techniques, several distinct forms of highly localized movements of ER were documented, categorized, and analyzed in terms of mechanism and structural implications. These include tubule branching, ring closure, and sliding. These localized movements have been observed to generate the basic elements of ER: linear tubules, polygonal reticulum, and triple junctions. We propose that as such they act as the mechanism for constructing the polygonal lattice of interconnected membrane tubules that constitutes ER. The nature of these movements suggests possible involvement of the cytoskeleton, and, in view of the close correlations in the distributions of ER and microtubules, and the accompanying paper (Dabora and Sheetz), it is possible that microtubules may play a role in generating ER motility and in constructing and maintaining the ER network in living cells.     

Specializations of endoplasmic reticulum in bovine placental cells

Summary The endoplasmic reticulum of mononuclear placental cells from 10 cows in different stages of pregnancy has been studied with the electron microscope. Basicaly the cryptal cells are provided with rough surfaced endoplasmic reticulum. In addition, whorls of rough or smooth cytomembranes encircle lipid droplets or plain cytoplasmic matrix. The trophoblastic cells also contain rough surfaced endoplasmic reticulum. Furthermore, skein-like conglomerations of smooth tubules are encountered in some cells. The significance of the membranous structures is discussed.This work was supported by the Swedish Medical Research Council (Project no K 68-12x-2494-01) and NIH General Research Support Grant FR05462.     

Dynamics of the endoplasmic reticulum in living non-muscle and muscle cells

The dynamic changes of the endoplasmic reticulum (ER) in interphase and mitotic cells was detected by the vital fluorescent dye 3,3'-dihexyloxacarbocyanine iodide. Two types of arrays characterize the continuous ER system in the non-muscle PtK2 cell: 1) a lacy network of irregular polygons and 2) long strands of ER that are found aligned along stress fibers. In cross-striated myotubes there was a periodic localization of fluorescence over each I-band corresponding to the positions of the terminal cisternae of the sarcoplasmic reticulum (SR). In contrast to the arrangement in muscle cells, the alignment of the long strands of ER alon stress fibers showed no strict periodicity that could be correlated with the sarcomeric units of the stress fibers. The ER and SR arrays seen in living cells were also detected in fixed cells stained with antibodies directed against proteins of the endoplasmic reticulum and sarcoplasmic reticulum, respectively. Observations of vitally stained PtK2 cells at 1 to 2 minute intervals using low light level video cameras and image processing techniques enabled us to see the polygonal ER units form and undergo changes in their shapes. During cell division, the ER, rhodamine 123-stained mitochondria, and phagocytosed fluorescent beads were excluded from the mitotic spindle while soluble proteins were not. No obvious concentration or alignment of membranes could be found associated with the contractile proteins in the cleavage furrow. After completion of cell division there was a redeployment of the ER network in each daughter cell.     

Nodal endoplasmic reticulum, a specialized form of endoplasmic reticulum found in gravity-sensing root tip columella cells

The endoplasmic reticulum (ER) of columella root cap cells has been postulated to play a role in gravity sensing. We have re-examined the ultrastructure of columella cells in tobacco (Nicotiana tabacum) root tips preserved by high-pressure freezing/freeze-substitution techniques to gain more precise information about the organization of the ER in such cells. The most notable findings are: the identification of a specialized form of ER, termed "nodal ER," which is found exclusively in columella cells; the demonstration that the bulk of the ER is organized in the form of a tubular network that is confined to a peripheral layer under the plasma membrane; and the discovery that this ER-rich peripheral region excludes Golgi stacks, vacuoles, and amyloplasts but not mitochondria. Nodal ER domains consist of an approximately 100-nm-diameter central rod composed of oblong subunits to which usually seven sheets of rough ER are attached along their margins. These domains form patches at the interface between the peripheral ER network and the ER-free central region of the cells, and they occupy defined positions within central and flanking columella cells. Over one-half of the nodal ER domains are located along the outer tangential walls of the flanking cells. Cytochalasin D and latrunculin A cause an increase in size and a decrease in numbers of nodal ER domains. We postulate that the nodal ER membranes locally modulate the gravisensing signals produced by the sedimenting amyloplasts, and that the confinement of all ER membranes to the cell periphery serves to enhance the sedimentability of the amyloplasts in the central region of columella cells.