The rough endoplasmic reticulum and the Golgi apparatus visualized using specific antibodies in normal and tumoral prolactin cells in culture

[From neuroendocrinology to cell biology: Andrée Tixier-Vidal]

This article relates the life, career and main scientific achievements of a pioneer in neuroendocrinology and French cell biology research, Mrs Andrée Tixier-Vidal, who passed away in December 2021. After her first works on hypophyseal-thyroid neuroendocrine axis, in birds then in mammals, Andrée Tixier-Vidal devoted herself then her group at the College of France to the histophysiological study of adenohypophysis and namely of prolactin (PRL) cells. Using in vitro models of organotypic cultures and cultures of GH3 cells, she described up to ultrastructural level the secretory process of PRL and its regulation by TRH. Furthermore, she extended her study to the TRH neurons themselves thanks to original models of in vitro cultures of hypothalamic neurons. Her fundamental and methodological achievements have largely contributed to major knowledge advances in cell biology of the secretion during the last century.

Contributions of Andrée Tixier-Vidal (1923-2021) to modern cell biology

This article illustrates the main stages of the scientific career of Dr Andrée Tixier-Vidal, a pioneer in cell biology research in France. She made important discoveries in the field of hormone secretion and neuronal morphogenesis. She played a key role in developing pituitary and neuronal cultures and using electron microscopy to study cellular structures. Her scientific influence continues to irradiate through her students and collaborators. This article is protected by copyright. All rights reserved.

Differential Expression of Markers and Activities in a Group of PC12 Nerve Cell Clones

Sixteen clones, recently isolated from the PC12 nerve cell line, were analysed for a variety of markers and activities. Two endoplasmic reticulum (ER) luminal markers, the chaperone protein BiP and the major Ca2+ storage protein calreticulin, as well as the 40-kD rough ER membrane marker and the plus-end-directed mirotubule motor protein, kinesin, were found to be expressed at similar levels. These results suggest that the size of the ER, the function of microtubules and the capacity of the rapidly exchanging Ca2+ store do not change substantially among the clones. Other proteins expressed at comparable levels were synapsin I and IIa, members of a nerve cell-specific protein family known to bind synaptic vesicles to the cytoskeleton. In contrast, another ER membrane protein, calnexin, and the markers of secretory organelles were found to vary markedly. One clone (clone 27) completely lacked both chromogranin B and secretogranin II, the proteins contained within dense granules, and synaptophysin, a marker of clear vesicles. Other clones expressed these markers to variable and apparently mutually unrelated levels. Marked variability was observed also in the uptake of exogenous catecholamines, in their release both at rest and after stimulation, and in nerve growth factor-induced differentiation. These results provide indirect information about the mechanisms that regulate the expression of structures and activities in PC12 cells. Of particular interest is clone 27, which appears globally incompetent for regulated secretion and might therefore be a valuable tool for the study of this activity in a nerve cell.

Receptor-mediated regulation of constitutive secretion

The traditional distinction between regulated and constitutive secretion may have contributed to the general belief that the latter is insensitive to extracellular modulatory signals. However, it now appears that signalling from membrane receptors can in fact modulate constitutive membrane traffic. In this article we discuss the molecular mechanisms, as well as the functional significance, of this modulation.

The endoplasmic reticulum-sarcoplasmic reticulum connection: distribution of endoplasmic reticulum markers in the sarcoplasmic reticulum of skeletal muscle fibers

The skeletal muscle sarcoplasmic reticulum (SR) was investigated for the presence of well-known endoplasmic reticulum (ER) markers: the lumenal protein BiP and a group of membrane proteins recognized by an antibody raised against ER membrane vesicles. Western blots of SR fractions revealed the presence of BiP in fast- and slow-twitch muscles of the rabbit as well as in rat and chicken muscles. Analyses of purified SR subfractions, together with cryosection immunofluorescence and immunogold labeling, revealed BiP evenly distributed within the longitudinal SR and the terminal cisternae. Within the terminal cisternae BiP appeared not to be mixed with calsequestrin but to be distributed around the aggregates of the latter Ca2+ binding protein. Of the various membrane markers only calnexin (91 kDa) was found to be distributed within both SR subfractions, whereas the other markers (apparent molecular masses of 64 kDa and 58 kDa and a doublet around 28 kDa) were concentrated in the terminal cisternae. These results suggest that the SR is a specialized ER subcompartment in which general markers, such as the ones we have investigated, coexist with the major SR proteins specifically responsible for Ca2+ uptake, storage, and release. The differential distribution of the ER markers reveals new aspects of the SR molecular structure that might be of importance for the functioning of the endomembrane system.

The endoplasmic reticulum of Purkinje neuron body and dendrites: molecular identity and specializations for Ca2+ transport

Immunofluorescence and immunogold labeling, together with sucrose gradient separation and Western blot analysis of microsomal subfractions, were employed in parallel to probe the endoplasmic reticulum in the cell body and dendrites of rat cerebellar Purkinje neurons. Two markers, previously investigated in non-nerve cells, the membrane protein p91 (calnexin) and the lumenal protein BiP, were found to be highly expressed and widely distributed to the various endoplasmic reticulum sections of Purkinje neurons, from the cell body to dendrites and dendritic spines. An antibody (denominated anti-rough-surfaced endoplasmic reticulum), which recognized two membrane proteins, p14 and p40, revealed a similar immunogold labeling pattern. However, centrifugation results consistent with a widespread distribution were obtained for p14 only, while p40 was concentrated in the rough microsome-enriched subfractions. The areas enriched in the inositol 1,4,5-triphosphate receptor and thus presumably specialized in Ca2+ transport (stacks of multiple smooth-surfaced cisternae; the dendritic spine apparatus) also exhibited labeling for BiP and p91, and were positive for the anti-rough-surfaced endoplasmic reticulum antibody (presumably via the p14 antigen). Additional antibodies, that yielded inadequate immunocytochemical signals, were employed only by Western blotting of the microsomal subfractions, while the ryanodine receptor was studied by specific binding. The latter receptor and the Ca2+ ATPase, known in other species to be concentrated in Purkinje neurons, exhibited bimodal distributions with a peak in the light and another in the heavy subfractions. A similar distribution was also observed with another lumenal protein, protein disulfide isomerase. Taken as a whole, the results that we have obtained suggest the existence in the endoplasmic reticulum of Purkinje neurons of two levels of organization; the first identified by widespread, probably general markers (BiP, p91, possibly p14 and others), the second by specialization markers, such as the inositol 1,4,5-triphosphate receptor and, possibly, p40, which appear restricted to areas where specific functions appear to be localized.

Ultrastructural observation of the trans-Golgi associated plate-like cisterna in the secretory cells of the rat anterior pituitary gland with special reference to the intracisternal skeleton

A well-developed plate-like cisterna (PLC) associated with trans-Golgi elements was observed in the Golgi apparatus of secretory cells in the rat anterior pituitary gland. This structure corresponds to the trans-most sacculotubular network. The PLC maintains a remarkably uniform thickness of about 33 nm, as measured between the outer leaflets of its unit membrane structure. As to the mechanism by which this peculiar construction of the PLC is maintained, pillar-like structures were noted in the PLC intracisternal space, apparently acting as supports to keep the intermembrane distance constant. The PLC was especially well developed in hypertrophied cells such as gonadotrophs following castration. One noteworthy feature was that the PLC frequently ran parallel with the rough endoplasmic reticulum (RER), maintaining a constant distance from the latter in hypertrophied cells, but no membrane continuity between the PLC and RER was seen.

Polypeptides of the Golgi apparatus of neurons from rat brain

An antiserum was raised against fractions of the Golgi apparatus of neurons from rat brain. Immunoblots of these fractions with the antiserum showed two principal bands of 185 and 150 kilodaltons (kd) in apparent molecular mass. The antiserum reacted with five or six bands of 200, 150, 130, 100-110, 64, and 40 kd in apparent molecular mass in immunoblots of several crude brain membrane fractions. Affinity-purified antibodies from the different gel bands transferred to nitrocellulose paper were used in immunoblot and immunocytochemical studies. Antibodies eluted from the 200-, 150-, 100-110-, and 64-kd bands reacted not only with the corresponding band but also with the other three bands. Antibodies eluted from the 40-kd band stained only the corresponding band. On light and/or electron microscopic immunocytochemistry, the antiserum stained the Golgi apparatus of rat neurons, glia, liver, and kidney tubule cells. Weaker, segmented, and less consistent staining was observed in nuclear envelopes, rough endoplasmic reticulum, and plasma membranes of neurons. Antibodies eluted from the bands at 200, 150, 100-110, and 64 kd stained intermediate cisterns of the Golgi apparatus of neurons. These findings suggest that a group of related polypeptides of brain membranes is preferentially expressed or enriched in the Golgi apparatus of neurons. Polypeptides with apparent molecular masses of 185 and 150 kd probably represent moieties endogenous to membranes of the neuronal Golgi apparatus.

The Golgi apparatus-complex of neurons and astrocytes studied with an anti-organelle antibody

An antiserum reacting with a 135-kDa antigen of rat liver Golgi apparatus-complex was used to stain, by light microscopic and ultrastructural immunocytochemistry, sections of rat cerebellum and by immunoblot homogenates of whole brain, isolated neurons and a fraction of enriched neuronal Golgi apparatus. In sections of rat cerebellum fixed with periodate-lysine-paraformaldehyde and immunostained with the direct peroxidase or peroxidase-antiperoxidase methods, the Golgi apparatus-complex in perikarya of neurons and glia was stained. Occasionally, nuclear envelopes and cisternae of the rough endoplasmic reticulum of neurons and glia were stained. Immunostain was not observed in peripheral dendrites, axons and presynaptic terminals. In striking contrast, peripheral smooth cisternae of astrocytic perikarya and processes were stained. Immunoblots of whole-brain membrane fractions, homogenates of isolated neurons and an enriched neuronal fraction of the Golgi apparatus-complex showed a principal single band of 64-kDa apparent mol. wt. We have concluded that the putative 64-kDa antigen(s) is distributed in cisternae of the Golgi apparatus-complex and occasionally in the nuclear envelope and rough reticulum, within the perikarya of neurons and glia. A second important distribution of the 64-kDa antigen(s), involving peripheral cisternae in perikarya and processes of astrocytes, is consistent with the hypothesis that the Golgi apparatus-complex of these cells extends to the periphery of these cells. The functional implications of the peripheral localization of the 64-kDa antigen(s) in astrocytes are discussed.

Immunological demonstration of intestinal absorption and digestion of protein macromolecules in the trout (Salmo gairdneri)

An immunofluorescence technique using antibodies against the Fc and Fab fragments of human IgG (IgGH) was used to study the absorption of proteins by the intestinal epithelial cells of rainbow trout after oral or anal administration. Cellular absorption of a high molecular weight protein, hepatitis-B surface antigen (HBsAg), was also studied by using two monoclonal antibodies, one specific for the confirmation of the antigen (implying disulfide bridges), and the other that reacts with the constituent polypeptides. Both absorbed IgGH and HBsAg were seen to be segregated in the apical vacuolar system, a characteristic feature of intestinal epithelial cells. The same antibodies were used with an everted sac technique in conjunction with immunofluorescence, to show the intravacuolar degradation of IgGH and HBsAg following absorption. By using an antibody against cathepsin D, it was possible to demonstrate, by immunofluorescence, the localization of this enzyme in the same vacuolar system. After coupling the antibody to peroxidase or to the protein A/colloidalgold complex, the ultrastructural antigenic sites of cathepsin D could be seen to be localized in the interior of the vacuoles. The vacuolar localization of a cathepsin B activity was determined by incubating sections of intestinal mucosa, or isolated epithelial cells, with a specific synthetic substrate (Z-Ala-Arg-Arg-methoxynaphthylamide). The supranuclear hyaloplasmic vacuoles of intestinal epithelial cells may be considered to be phagolysosomes that assure the degradation of absorbed proteins. This function may be of fundamental importance in the in the nutritional processes of this species.

Use of pre-embedding ultrastructural immunocytochemistry in the localization of a secretory product and membrane proteins in cultured prolactin cells

A pre-embedding immunoperoxidase procedure performed directly on cultured cells in situ was used to localize several intracellular antigens at the electron-microscope level. With this procedure, we compared the effect of various fixatives, with or without saponin permeabilization, on the immunoreactivity of a secretory product (prolactin) and membrane proteins in cultured prolactin cells. Prolactin was detected within all compartments of its intracellular secretory pathway. Membrane antigens of the rough endoplasmic reticulum, the Golgi apparatus, and lysosomes were localized in distinct intracellular compartments. These immunocytochemical results are discussed in relationship to others in the literature that describe the localization of similar types of antigens. The technique, here described, which preserves ultrastructural detail and antigenicity, should be applicable for the localization of other intracellular antigens in cultured cells.

Identification of a transmembrane glycoprotein specific for secretory vesicles of neural and endocrine cells

Several types of cells store proteins in secretory vesicles from which they are released by an appropriate stimulus. It might be expected that the secretory vesicles in different cell types use similar molecular machinery. Here we describe a transmembrane glycoprotein (Mr approximately 100,000) that is present in secretory vesicles in all neurons and endocrine cells studied, in species from elasmobranch fish to mammals, and in neural and endocrine cell lines. It was detected by cross-reactivity with monoclonal antibodies raised to highly purified cholinergic synaptic vesicles from the electric organ of fish. By immunoprecipitation of intact synaptic vesicles and electron microscopic immunoperoxidase labeling, we have shown that the antigenic determinant is on the cytoplasmic face of the synaptic vesicles. However, the electrophoretic mobility of the antigen synthesized in the presence of tunicamycin is reduced to Mr approximately 62,000, which suggests that the antigen is glycosylated and must therefore span the vesicle membrane.

Antibodies against a lysosomal membrane antigen recognize a prelysosomal compartment involved in the endocytic pathway in cultured prolactin cells

Antibodies against a lysosomal membrane antigen (A-Ly-M) have recently been obtained and characterized (Reggio, H., D. Bainton, E. Harms, E. Coudrier, and D. Louvard, 1984, J. Cell Biol., 99:1511-1526). They recognize a 100,000-mol-wt antigen immunologically related to a purified [H+,K+]ATPase from pig gastric mucosa. In the present study, we have localized this antigen during adsorptive endocytosis in rat prolactin cells in culture using cationized ferritin (CF) as a tracer. CF was rapidly internalized (after 5 min) in coated pits and vesicles that were labeled by antibodies against clathrin. The tracer was then delivered (after 15 min) to vacuoles and multivesicular bodies. These structures were labeled with A-Ly-M. These organelles were devoid of acid phosphatase activity. At later stages (after 30 min) CF was observed within larger structures that were strongly stained by A-Ly-M and displayed a strong acid phosphatase activity. These findings clearly indicate that A-Ly-M react with prelysosomal and lysosomal compartments involved in the endocytic pathway in cultured prolactin cells. The membrane of these structures therefore contains antigenic determinant(s) related to the 100,000-mol-wt polypeptide. Our results suggest that the prelysosomal structure stained by A-Ly-M may represent in GH3 cells the acidic prelysosomal compartment recently described in the early steps of endocytosis in other cell types (Tycko, B., and F. R. Maxfield, 1982, Cell, 28:643-651).

Uptake of lectins by pulmonary alveolar type II cells: subsequent deposition into lamellar bodies

Type II cells of the alveolar epithelium of adult rats have been shown to internalize the ferritin-labeled lectin from Maclura pomifera (MPA-F). This alpha-galactose-binding molecule binds specifically to the apical plasma membrane of the cells. Once within the cell the lectin is cycled from pinocytic vesicles, to multivesicular bodies of two types, and finally to lamellar bodies, the storage granules of surfactant. Those multivesicular bodies that first contain MPA-F lack detectable lysosomal enzymes, while those labeled later are reactive. For 30-60 min, uptake of MPA-F is blocked by adding methyl alpha-D-galactoside to the instillate. Lectins that have no or limited binding to type II cells are taken up in amounts similar to fluid phase markers. These observations indicate that type II cells can take up substances from alveoli by the process of adsorptive endocytosis and deposit the ingested material into lamellar bodies.

Endogenous and monoclonal antibodies to the rat pancreatic acinar cell Golgi complex

Normal, unimmunized mouse serum from several strains (BALB/c, C57/b, DBA/2, NZB, SJL, CD/1) contains an endogenous IgG antibody that localizes to the Golgi complex of rat pancreatic acinar cells. Treatment of pancreatic acini with 5 microM monensin resulted in the swelling and vacuolization of the Golgi cisternae, and in a corresponding annular staining by the mouse serum as observed by immunofluorescence, suggesting that the antigen recognized is on the Golgi complex cisternal membrane. The antiserum did not react with pancreatic secretory proteins, and its binding to smooth microsomal membranes was retained following sodium carbonate washing, supporting a Golgi membrane localization. Advantage was taken of the existence of the endogenous murine antibody for the isolation of monoclonal antibodies directed to the Golgi complex of the rat pancreas. Two antibodies, antiGolgi 1 and antiGolgi 2, are described. Both antibodies are IgMs that recognize integral membrane proteins of the trans-Golgi cisternae, with lighter and patchy staining of the pancreatic lumen membrane, as observed both by light and electron microscopy. AntiGolgi 1 recognizes predominately a protein of molecular weight 103,000-108,000, whereas antiGolgi 2 shows a strong reaction to a 180-kd band as well as the 103-108-kd protein.