Association of mitochondria with intermediate filaments and of polyribosomes with cytoplasmic actin

Summary Anti-mitochondrial autoantibody and fluorescent derivatives of insulin stain phase-dense mitochondria in acetone-fixed monolayers of fibroblasts. Double fluorochrome studies show mitochondria in close topographic association with intermediate filaments. In cells treated with vinblastine or colchicine, mitochondria are relocated in sites closely associated with coils of perinuclear intermediate filaments. In contrast, autoantibody to polyribosomes stains granules aligned in the long axis of well spread embryonic cells, in the direction of actin-containing fibrils, an arrangement that is lost in cells pretreated with the actin filament disrupting drug cytochalasin B. In more mature fibroblasts, antiribosomal antibody reacts with phase-dense rough endoplasmic reticulum and this staining pattern is not affected by cytochalasin B. The observations suggest that mitochondria are associated with intermediate filaments and that free polyribosomes, but not polyribosomes attached to rough endoplasmic reticulum, are associated with cytoplasmic actin.Supported by a grant from the Anti-Cancer Council of Victoria. We thank Mrs. I. Burns for technical assistance and Dr. H.A. Ward and staff for preparation of fluorescent conjugates     

CPT1c is localized in endoplasmic reticulum of neurons and has carnitine palmitoyltransferase activity

CPT1c is a carnitine palmitoyltransferase 1 (CPT1) isoform that is expressed only in the brain. The enzyme has recently been localized in neuron mitochondria. Although it has high sequence identity with the other two CPT1 isoenzymes (a and b), no CPT activity has been detected to date. Our results indicate that CPT1c is expressed in neurons but not in astrocytes of mouse brain sections. Overexpression of CPT1c fused to the green fluorescent protein in cultured cells demonstrates that CPT1c is localized in the endoplasmic reticulum rather than mitochondria and that the N-terminal region of CPT1c is responsible for endoplasmic reticulum protein localization. Western blot experiments with cell fractions from adult mouse brain corroborate these results. In addition, overexpression studies demonstrate that CPT1c does not participate in mitochondrial fatty acid oxidation, as would be expected from its subcellular localization. To identify the substrate of CPT1c enzyme, rat cDNA was overexpressed in neuronal PC-12 cells, and the levels of acylcarnitines were measured by high-performance liquid chromatography-mass spectrometry. Palmitoylcarnitine was the only acylcarnitine to increase in transfected cells, which indicates that palmitoyl-CoA is the enzyme substrate and that CPT1c has CPT1 activity. Microsomal fractions of PC-12 and HEK293T cells overexpressing CPT1c protein showed a significant increase in CPT1 activity of 0.57 and 0.13 nmol.mg(-1).min(-1), respectively, which is approximately 50% higher than endogenous CPT1 activity. Kinetic studies demonstrate that CPT1c has similar affinity to CPT1a for both substrates but 20-300 times lower catalytic efficiency.     

Effects of thyroidectomy, propylthiouracil, and thyroxine on pituitary content and immunocytochemical staining of thyrotropin (TSH) and thyrotropin releasing hormone (TRH)

Previous studies have demonstrated immunocytochemical staining for beta chains of thyroid stimulating hormone (TSH-beta) in rough endoplasmic reticulum of pituitary cells hypertrophied after thyroidectomy ("thyroidectomy cells") (Moriarty CG(1976): J Histochem Cytochem (24:846; Moriarty GC, Tobin RB (1976): J Histochem Cytochem 24:1140). Here we report the localization of thyrotropin releasing hormone (TRH) in serial sections of the same pituitaries to determine if it could be found at similar sites. No staining for TRH was found in hypertrophied TSH cells formed 42 days after the surgery, or after 14, 34, and 70 days of propylthiouracil (PTU) treatment. The loss in immunostaining in the PTU-treated rats was correlated with radioimmunoassay (RIA) measurements that showed a 65% reduction in anterior pituitary TRH content after 34, 70, and 98 days of PTU treatment (from 22.9--7.8 pg/mg wet wt) and a 50% reduction in TSH content after 34 days of treatment. When thyroxine was administered to hypothyroid rats for 3 days before death, our previous studies had demonstrated intense staining for TSH in granules inside the rough endoplasmic reticulum. In this study, the radioimmunoassay showed that TSH content rose dramatically in the hypothyroid animals treated with PTU for 77 days and thyroxine for 2 days before death (from 8.5--64.1 mU/mg wet wt); however, the rise in TRH content was minimal (5.8--9.8 pg/mg wet wt). The immunocytochemical stain for TRH correlated well with the RIA showing a weak reaction mainly on small granules in the cytoplasm. No reaction for TRH was found in rough endoplasmic reticulum. These results suggest that TRH and TSH storage sites are dissimilar in the hypothyroid rat. The presence of stain for TRH in granules in the cytoplasm suggests that it might play a role in the storage or packaging of TSH. Its absence in profiles of rough endoplasmic reticulum staining intensely for TSH suggests that it is not synthesized at this site. No definite conclusions about its origin can be drawn at this time.     

Ultrastructural localization of acetylcholinesterase activity in primary cultures of rat substantia nigra

Summary Ultrastructural localization of acetylcholinesterase activity was studied in primary cultures of the substantia nigra microdissected from newborn rat brains. Light microscopic observations were also made on the characteristics of dopamine neurones and acetylcholinesterase containing cells in these cultures. Ultrastructurally acetylcholinesterase activity was localized in the nuclear envelope and rough endoplasmic reticulum of neurones, which had deeply infolded, round or oval nucleus, a prominent Golgi apparatus and varying amounts of rough endoplasmic reticulum. In the neuropil acetylcholinesterase activity was seen within microtubules of neuronal processes and in the rough endoplasmic reticulum of dendrites. The enzyme activity was also demonstrated within the nuclear envelope and rough endoplasmic reticulum of probably capillary endothelial cells. Dopaminergic neurones were identified on the basis of the green catecholamine fluorescence they exhibited. Small dopaminergic neurones could be observed and there was indirect evidence that these cells did not stain for acetylcholinesterase.     

Ultrastructural location of albumin and fibrinogen in primary cultures of new-born rat liver tissue

In primary cultures of new-born rat liver tissue, albumin and frbrinogen, two proteins normally synthesized by the liver and secreted into plasma were demonstrated by specific antibodies labelled with peroxidase in about 50 and 70% of the hepatocytes; these proteins were not demonstrated in the other types of cells, in particular fibroblasts, present in primary cultures. These two proteins were detected on the ribosomes of the rough endoplasmic reticulum and were also present in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus. It is concluded that

1. 1. In primary cultures of liver tissue, only the hepatocytes synthesize albumin and fibrinogen.

2. 2. Proliferating cultured hepatocytes are able to synthesize albumin and fibrinogen.

3. 3. The presence of detectable albumin and fibrinogen in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus in hepatocytes of primary cultures and their absence in the lumina of the rough and smooth endoplasmic reticulum and in the Golgi apparatus in the hepatocytes of adult rat liver might indicate an alteration in the translocation of albumin and fibrinogen through these organelles in cultured hepatocytes.

     

Light and electron microscopic immunocytochemistry on the localization of 3 beta-hydroxysteroid dehydrogenase/isomerase in the bovine adrenal cortical cells

The localization of 3 beta-hydroxysteroid dehydrogenase/isomerase (3 beta-HSD) was studied in bovine adrenal glands by light as well as electron microscopic immunocytochemistry, using anti-bovine adrenal 3 beta-HSD antibody. With light microscopy the cytoplasm of the glomerulosa cells was weakly immunostained, while that of the fasciculata-reticularis cells was intensely immunostained though both the capsular connective tissue cells and the medullary cells were entirely negative for this reaction. Electron microscopic immunocytochemistry revealed that the positive reaction products for 3 beta-HSD were present on the membrane of smooth endoplasmic reticulum of the cortical cells, especially that of the fasciculata and reticularis cells. Other cell organelles such as mitochondria and Golgi apparatus were entirely negative. The present results indicate that 3 beta-HSD is present in the membrane of smooth endoplasmic reticulum of bovine adrenal cortical cells.     

The pineal region in the opossum,Didelphis virginiana

Summary In the pineal region of the opossum, Didelphis virginiana, two types of cells predominate: 1) pinealocytes, and 2) fibrous astrocytes. Pinealocytes are characterized by the presence of prominent Golgi bodies, numerous clear and dense-cored vesicles, sensory cilia (9+0), vesicle-crowned rods, and condensation of a material that was always associated with the rough endoplasmic reticulum. In addition, two other cell types are occasionally seen. These include 1) neuron-like cells, and 2) darker staining cells of unknown identity. The endoplasmic reticulum of the darker staining cells is typically expanded and filled with an amorphous substance. Although the pineal region is small in size, the present findings suggest that pinealocytes in this species are metabolically active cells displaying a secretory function. Moreover, the presence of sensory cilia (9+0) and vesicle-crowned rods indicates that pinealocytes of the opossum are phylogenetically related to the photoreceptor cells found in the pineal organ of lower vertebrates.     

Immunolocalization of von Willebrand protein in Weibel-Palade bodies of human endothelial cells

Immunofluorescence staining of cultured human umbilical vein endothelial cells has shown the presence of von Willebrand protein in the perinuclear region, in small rodlike structures through the cytoplasm, and on filaments of the extracellular matrix. Nonendothelial cells showed no staining with anti-von Willebrand protein antiserum. At the light microscope level, immunoperoxidase treatment of endothelial cells revealed the same pattern and antibody specificity as the fluorescence staining. Thin sections of the peroxidase-stained cells showed decorated filaments close to the substratum and also specific deposits in the endoplasmic reticulum and Weibel-Palade bodies. Control antisera against other selected proteins in endothelial cells failed to stain the Weibel-Palade bodies. These data suggest that the Weibel- Palade bodies of endothelial cells are storage and/or processing organelles for von Willebrand protein.     

Establishment of a new human thyroid medullary carcinoma cell line. Morphological studies

A new human medullary carcinoma cell line has been established from a thyroid tumor removed from a 76-year-old female patient. The cultured cells grew in suspension, formed round islands and did not attach to the plastic dish. The doubling time of 48 h is the shortest recorded for C-cell lines. Ultrastructural studies disclosed that the cells had a few short profiles of rough endoplasmic reticulum, numerous ribosomes and polyribosomes, a poorly developed Golgi apparatus and small secretory granules (75 nm in mean diameter). Immunohistochemical staining for somatostatin was positive. These results show that, compared with previously established C-cell lines, this cell line has a rapid growth rate, is morphologically less differentiated, but retains a hormone production potential.     

Morphology of the reproductive system of the armadillo. The spermatogonia

Spermatogonia of the nine-banded armadillo, Dasypus novemcinctus mexicanus, were studied morphologically using light and electron microscopy and examined histochemically using light microscopy. Immature flat type spermatogonia have ovoid or irregular nuclei with loosely condensed chromatin. Free ribosomes are abundant while profiles of rough endoplasmic reticulum are scarce. Smooth endoplasmic reticulum is a prominent feature occasionally taking an unusual cylindrical form. Mature spermatogonia exhibit rounder nuclei with greater degrees of chromatin clumping. Smooth endoplasmic reticulum is no longer prominent whereas profiles of rough endoplasmic reticulum are quite common. Occasional lysosomal configurations are found in mature spermatogonia. The majority of spermatogonial cells exhibit weak to moderate reactivity when stained with the periodic acid-Schiff (PAS) reaction. Certain cells in each tubular cross section stain vividly with this reaction and the PAS positivity is removable with salivary amylase. Because of nuclear characteristics, position of the cell immediately upon the basal lamina, intensity of the PAS reaction and the relative paucity of the vividly staining cells, it is suggested that they are members of the immature spermatogonial cell line, perhaps acting as stem cells. None of the several other histochemical procedures employed was capable of selectively demonstrating these cells.     

Protein-carboxyl methylation in adrenal medullary cells

1. The protein-carboxyl methylating system has been studied in adrenal medullary cells either using disrupted cell components or with intact cells. Whereas the enzyme protein-carboxyl methylase (PCM) is cytosolic, the majority of its substrates is on or within chromaffin granules. With intact granules, methylation of surface proteins results in solubilization of membrane proteins. 2. Membrane PCM substrates have been identified as two proteins with apparent molecular weights of 55,000 and 32,000. Among the substrates located inside the granules, the chromogranins are excellent substrates, while dopamine beta-hydroxylase is poorly methylated. 3. Under physiological conditions, stimulation of the splanchnic nerve results in an increase in adrenal medullary protein-methyl ester formation as well as in an augmented methanol production. With adrenal medullary cells in culture, carboxyl-methylated chromogranin A is detected in mature chromaffin granules between 3 and 6 hr after labeling. Methylated chromogranins are secreted concomitantly with catecholamines following cholinergic stimulation. 4. These data coupled with those of Chelsky et al. (J. Biol. Chem. 262:4303-4309, 1987) on lamin B suggest that PCM methylates residues other than D-aspartyl and L-isoaspartyl in proteins. They further suggest that methylation may occur on nascent peptide chains before they are injected into the rough endoplasmic reticulum.     

Rapid formation of inositol 1,4,5-trisphosphate in rat pancreatic acini stimulated by carbamylcholine

Cholinergic stimulation of inositol phosphate formation was studied in isolated rat pancreatic acini, prelabelled with myo-[2-3H]inositol. Carbamylcholine increased incorporation of radioactivity into Ins(1,4,5)P3 and InsP4 within 5 s. Increases in [3H]Ins(1,3,4)P3 were delayed with marked stimulation occurring between 10 s and 1 min. Inositol polyphosphate formation was less sensitive to carbamylcholine concentration than was stimulation of amylase release. At a low (0.3 microM) carbamylcholine concentration, no increase in inositol polyphosphate formation was detected, whereas stimulation of amylase release, which was not dependent on extracellular calcium, was observed. Ins(1,4,5)P3 was shown to release actively accumulated 45Ca2+ from isolated rough endoplasmic reticulum membranes to a similar extent as that released from rough endoplasmic reticulum following cholinergic stimulation of pancreatic acini (Richardson, A.E. et al. (1984) Biochem. Soc. Trans. 12, 1066-1067). The data is consistent with Ins(1,4,5)P3 being produced rapidly enough to release sufficient calcium from the rough endoplasmic reticulum to cause an observed increases in cytoplasmic free Ca2+.     

The eta isoform of protein kinase C is localized on rough endoplasmic reticulum.

The eta isoform of protein kinase C, isolated from a cDNA library of mouse skin, has unique tissue and cellular distributions. It is predominantly expressed in epithelia of the skin, digestive tract, and respiratory tract in close association with epithelial differentiation. We report here that this isoform is localized on the rough endoplasmic reticulum in transiently expressing COS1 cells and constitutively expressing keratinocytes. By the use of polyclonal antibodies raised against peptides of the diverse D1 and D2/D3 regions, we found that immunofluorescent signals were strongest in the cytoplasm around the nucleus and became weaker toward the peripheral cytoplasm. Under immunoelectron microscopic examination, electron-dense signals were located on the rough endoplasmic reticulum and on the outer nuclear membrane which is continuous with the endoplasmic reticulum membrane. However, no signals were detected in the nucleus, inner nuclear membrane, smooth endoplasmic reticulum, Golgi apparatus, mitochondria, or plasma membrane. Treatment of the cells in situ with detergents suggested association of the isoform of protein kinase C with intracellular structures. By immunoblotting, a distinct single band with an M(r) of 80,000 was detected in whole-cell lysate and in rough microsomal and crude nuclear fractions, all of which contain outer nuclear membrane and/or rough endoplasmic reticulum. We further demonstrated the absence of a nuclear localization signal in the pseudosubstrate sequence. The present observation is not consistent with the report of Greif et al. (H. Greif, J. Ben-Chaim, T. Shimon, E. Bechor, H. Eldar, and E. Livneh, Mol. Cell. Biol. 12:1304-1311, 1992).     

Localization of the Noradrenaline Transporter in Rat Adrenal Medulla and PC12 Cells

The noradrenaline transporter (NAT) is present in noradrenergic neurons and a few other specialized cells such as adrenal medullary chromaffin cells and the rat pheochromocytoma (PC12) cell line. We have raised antibodies to a 49-residue segment (NATM2) of the extracellular region (residues 184-232) of bovine NAT. Affinity-purified NATM2 antibodies specifically recognized an 80-kDa band in PC12 cell membranes by western blotting. Bands of a similar size were also detected in membranes from human neuroblastoma (SK-N-SH) cells expressing endogenous NAT and human embryonic kidney (HEK293) cells stably expressing bovine NAT. Immunocytochemistry of rat adrenal tissue showed that NAT staining was colocalized with tyrosine hydroxylase in medullary chromaffin cells. Most NAT immunoreactivity in rat adrenal chromaffin and PC12 cells was present in the cytoplasm and had a punctate appearance. Cell surface biotinylation experiments in PC12 cells confirmed that only a minor fraction of the NAT was present at the cell surface. Subcellular fractionation of PC12 cells showed that relatively little NAT colocalized with plasma membrane, synaptic-like microvesicles, recycling endosomes, or trans-Golgi vesicles. Most of the NAT was associated with [3H]noradrenaline-containing secretory granules. Following nerve growth factor treatment, NAT was localized to the growing tip of neurites. This distribution was similar to the secretory granule marker secretogranin I. We conclude that the majority of NAT is present intracellularly in secretory granules and suggest that NAT may undergo regulated trafficking in PC12 cells.     

Simultaneous apocrine and merocrine secretion in the rat coagulating gland

The coagulating gland of the rat synthesizes two prevalent secretory proteins (transglutaminase and 115 K) that are discharched in a different manner, one being secreted in an apocrine fashion (transglutaminase) and the other one in a merocrine way (115 K). Differences in the intra- cellular pathway and the release of either protein were studied using immunofluorescence on semithin sections, immunoelectron microscopy of preembedding-processed chopper sections and postembedding-processed ultrathin sections of rat coagulating gland. Immunohistochemical staining using an anti-transglutaminase antibody resulted in dense labeling of the cytoplasm of secretory cells and their apical blebs, whereas the cisternae of the rough endoplasmic reticulum and the Golgi apparatus were completely unlabeled. When, on the contrary, the anti-115 K antiserum was used, dense labeling of the cisternae of the rough endoplasmic reticulum, the Golgi apparatus, and the secretory granules was seen. Intraluminal secretion was also labeled, but the secretory blebs remained unlabeled. Our findings show that, in the coagulating gland of the male rat, the two secretory proteins studied are processed in parallel, but at completely different intracellular pathways. They are released via different extrusion mechanisms. Transglutaminase is synthesized outside the endoplasmic reticulum, reaches the apical cell pole by free flow in the cytoplasm, and is released via apocrine blebs, the membranes of which appear to be derived from the apical plasma membrane. The protein 115 K, on the other hand, follows the classic route, being synthesized within the cisternae of rough endoplasmic reticulum, subsequently glycosylated in the Golgi apparatus, and released in a merocrine fashion. The mutual exclusion of the two secretory pathways and the regulation of the alternative release mechanism are still unresolved issues.     

A chymotrypsin-type serine protease in rat basophilic leukemia cells: evidence for its immunologic identity with atypical mast cell protease

Activity of a chymotrypsin-type serine protease was found in a subline of rat basophilic leukemia (RBL-2H3) cells. The protease was immunologically cross-reactive with anti-atypical mast cell protease immunoglobulin (Ig) G, and its activity was inhibited in a dose-dependent manner by the antibody. The apparent m.w. of the protease that reacted with the antibody was 25,000, which was identical with that of atypical mast cell protease in rat mucosal mast cells. These results show that the chymotrypsin type serine protease in RBL-2H3 cells is immunologically identical with atypical mast cell protease, which was first purified from rat small intestine. Immunohistochemical studies showed that the protease was located not only in intracytoplasmic granules but also in organelles synthesizing protein, such as cisternae of the rough endoplasmic reticulum, perinuclear spaces, and the Golgi apparatus. However, no immunoreactivity was demonstrated in rat basophils. The activity of the protease increased in the exponential phase of growth of RBL-2H3 cells in which some activity was also detected in the medium, and it decreased in the late stationary phase.     

Differential expression of ACAT1 and ACAT2 among cells within liver, intestine, kidney, and adrenal of nonhuman primates

Two closely related enzymes with more than 50% sequence identity have been identified that catalyze the esterification of cholesterol using acyl-CoA substrates, namely acyl-CoA:cholesterol acyltransferase 1 (ACAT1) and ACAT2. Both are membrane-spanning proteins believed to reside in the endoplasmic reticulum of cells. ACAT2 has been hypothesized to be associated with lipoprotein particle secretion whereas ACAT1 is ubiquitous and may serve a more general role in cellular cholesterol homeostasis. We have prepared and affinity purified rabbit polyclonal antibodies unique to either ACAT enzyme to identify their cellular localization in liver and intestine, the two main lipoprotein-secreting tissues of the body, and for comparison, kidney and adrenal. In the liver, ACAT2 was identified in the rough endoplasmic reticulum of essentially all hepatocytes whereas ACAT1 was confined to cells lining the intercellular spaces among hepatocytes in a pattern typical of Kupffer cells. In the intestine, ACAT2 signal was strongly present in the apical third of the mucosal cells, whereas ACAT1 staining was diffuse throughout the mucosal cell, but with strong signal in goblet cells, Paneth cells, and villus macrophages. In the kidney, ACAT1 immunostaining was specific for the distal tubules and podocytes within the glomerulus. In the adrenal, ACAT1 signal was strongly present in the cells of the cortex, and absent from other adrenal cell types. No ACAT2 signal was identified in the kidney or adrenal.We conclude that only the cells of the liver and intestine that secrete apolipoprotein B-containing lipoproteins contain ACAT2, whereas ACAT1 is present in numerous other cell types. The data clearly suggest separate functions for these two closely related enzymes, with ACAT2 being most closely associated with plasma cholesterol levels.     

Calcium-ion-transporting activity in two microsomal subfractions from rat pancreatic acini. Modulation by carbamylcholine

Two microsomal subfractions from isolated rat pancreatic acini were produced by centrifugation through a discontinuous sucrose density gradient and characterized by biochemical markers. The denser fraction ( SF2 ) was a highly purified preparation of rough endoplasmic reticulum; the less-dense fraction ( SF1 ) was heterogeneous and contained Golgi, endoplasmic reticulum and plasma membranes. 45Ca2+ accumulation in the presence of ATP and its rapid release after treatment with the bivalent-cation ionophore A23187 were demonstrated in both fractions. The pH optimum for active 45Ca2+ uptake was approx. 6.8 for the rough endoplasmic reticulum ( SF2 ) and approx. 7.5 for SF1 . Initial rate measurements were used to determine the affinity of the rough-endoplasmic-reticulum uptake system for free Ca2+. An apparent Km of 0.16 +/- 0.06 microM and Vmax. of 21.5 +/- 5.6 nmol of Ca2+/min per mg of protein were obtained. 45Ca2+ uptake by SF1 was less sensitive to Ca2+, half-maximal uptake occurring at 1-2 microM-free Ca2+. When fractions were prepared from isolated acini stimulated with 3 microM-carbamylcholine, 45Ca2+ uptake was increased in the rough endoplasmic reticulum. The increased uptake was due to a higher Vmax. with no significant change in Km. No effect was observed on 45Ca2+ uptake by SF1 . In conclusion, two distinct non-mitochondrial, ATP-dependent calcium-uptake systems have been demonstrated in rat pancreatic acini. One of these is located in the rough endoplasmic reticulum, but the precise location of the other has not been determined. We have shown that the Ca2+-transporting activity in the rough endoplasmic reticulum may have an important role in maintaining the cytosolic free Ca2+ concentration in resting acinar cells and is involved in Ca2+ movements which occur during stimulation of enzyme secretion.     

Immunocytochemical staining of supraoptic neurons from homozygous Brattleboro rats by use of antibodies against two domains of the mutated vasopressin precursor

Summary By use of an antibody against the 14 amino acids in the mutated vasopressin precursor (CP-14) characteristic of the homozygous Brattleboro rat, an immunohisto- and-cytochemical study was performed on the supraoptic nuclei of homozygous Brattleboro rats. At the light-microscopic level, varying numbers of perikarya per section exhibited a positive reaction. The most intense staining was observed in a patchy manner on the peripheral portions of the cytoplasm, its central portion being stained less intensely. The antiserum did not react with the supraoptic perikarya of the Wistar rat. In the homozygous Brattleboro rat, antibodies against normal vasopressin only rarely resulted in a positive immunoreaction. However, when it was observed, incubation of the subsequent section with CP-14-antiserum suggested a co-localization of both peptides in the same perikaryon. At the ultrastructural level, CP-14 immunoreactivity was demonstrated on the secretory cisternae of the Golgi apparatus, on lysosome-like bodies and on parts of the rough endoplasmic reticulum. With the use of an antibody against normal vasopressin, immunoreactivity was confined to very limited areas of the rough endoplasmic reticulum. The oxytocin immunoreactivity in supraoptic perikarya of Brattleboro rats did not differ from that in the Wistar rat, either at the light- or at the electron-microscopic levels.     

The beads in the Golgi complex-endoplasmic reticulum region

The region between the rough endoplasmic reticulum (ER) and the Golgi complex has been studied in a variety of insect cell types in an attempt to find a marker for the exit gate or gates from the ER. We have found that the smooth surface of the rough endoplasmic reticulum near Golgi complex transitional elements has beadlike structures arranged in rings at the base of transition vesicles. They occur in all insect cell types and a variety of other organisms. The beads can be seen only after staining in bismuth salts. They are 10-12 nm in diameter and are separated from the membrane and one another by a clear halo giving them a center to center spacing of about 27 nm. The beads are not sensitive to nucleases under conditions which disrupt ribosomes or remove all Feulgen staining material from the nucleus. Under conditions similar to those used to stain tissue, bismuth does not react in vitro with nucleic acids. The component of the beads that stains preferentially with bismuth is therefore probably not nucleic acid.