Migration of glycoprotein from the Golgi apparatus to the surface of various cell types as shown by radioautography after labelled fucose injection into rats

Differential mucins secretion by intestinal mucous cells of Chelon ramada in response to an enteric helminth Neoechinorhynchus agilis (Acanthocephala)

Intestinal mucous cells produce and secrete mucins which hydrate, lubricate and protect the intestinal epithelium from mechanical injuries due to the transition of digesta or action of pathogens. Intestinal mucous cells are considered elements of the innate immune system as they secrete lectins, toxins, immunoglobulins, and anti-microbial peptides. Acid mucins can surround and eliminate many pathogenic microorganisms. We performed a quantitative analysis of the density and mucus composition of different intestinal mucous cell types from mullet (Chelon ramada) that were infected solely with Neoechinorhynchus agilis. Most N. agilis were encountered in the middle region of the intestine. Mucous cell types were identified with Alcian Blue (pH2.5) and Periodic acid-Schiff (PAS) histochemistry, and by staining with a panel of seven lectins. Mucus enriched for high viscosity acid mucins was accumulated near points of worm attachment. Parasites were surrounded by an adherent mucus layer or blanket. Ultrastructural examination showed intestinal mucous cells typically possessed an elongated, basally positioned nucleus and numerous electron dense and lucent vesicles in the cytoplasm. The results show both an increase in mucus production and changes in mucin composition in infected mullet in comparison with uninfected conspecifics.

The Secretion and Action of Brush Border Enzymes in the Mammalian Small Intestine

Microvilli are conventionally regarded as an extension of the small intestinal absorptive surface, but they are also, as latterly discovered, a launching pad for brush border digestive enzymes. Recent work has demonstrated that motor elements of the microvillus cytoskeleton operate to displace the apical membrane toward the apex of the microvillus, where it vesiculates and is shed into the periapical space. Catalytically active brush border digestive enzymes remain incorporated within the membranes of these vesicles, which shifts the site of BB digestion from the surface of the enterocyte to the periapical space. This process enables nutrient hydrolysis to occur adjacent to the membrane in a pre-absorptive step. The characterization of BB digestive enzymes is influenced by the way in which these enzymes are anchored to the apical membranes of microvilli, their subsequent shedding in membrane vesicles, and their differing susceptibilities to cleavage from the component membranes. In addition, the presence of active intracellular components of these enzymes complicates their quantitative assay and the elucidation of their dynamics. This review summarizes the ontogeny and regulation of BB digestive enzymes and what is known of their kinetics and their action in the peripheral and axial regions of the small intestinal lumen.

Glycohistochemical characterization of histologically normal nasal mucosa and enzootic nasal tumor of sheep

OBJECTIVE

To determine glycohistochemical characteristics of enzootic nasal tumors (ENTs) of sheep, compare results for ENT with those of histologically normal nasal mucosa of sheep, and identify the histologic origin of ENT.

SAMPLE

ENT and nasal mucosa samples obtained from cadavers of 5 adult Lacaune sheep with ENT and 5 Lacaune sheep unaffected by ENT, respectively.

PROCEDURES

Samples of ENT and nasal mucosa were collected from cadavers of sheep and sectioned. Conventional and lectin histochemical analyses were used to identify glycoconjugates in tissue sections on the basis of their principal chemical groups and principal terminal or internal oligosaccharidic glucidic residues, respectively.

RESULTS

ENTs had papillary and tubular portions. Cells in the papillary portion of ENTs had secretion and surface glycoconjugates, which included sulfated glycosaminoglycans and neutral and sialilated glycoproteins. Cells in the tubular portion of ENTs had surface glycoconjugates, which included neutral and sialilated glycoproteins. Both portions of ENTs had C(4)-acetylated sialoderivatives that were not detected in sections of histologically normal nasal mucosa.

CONCLUSIONS AND CLINICAL RELEVANCE

The papillary portion of ENTs in sheep may originate from respiratory glands and goblet cells. The tubular portion of ENTs in sheep may originate from olfactory glands. Presence of C(4)-acetylated sialoderivatives in cells of ENTs could confer resistance against pathogens to those cells.

Morphology and lectin-binding sites of pyloric caeca epithelium in normal and GnRH-treated Atlantic bluefin tuna (Thunnus thynnus) Linnaeus 1758

Mucosal epithelium of pyloric caeca was studied in normal and in GnRH-treated Atlantic bluefin tuna Thunnus thynnus L., using morphological analysis, conventional and lectin glycohistochemistry. The lining epithelium consisted of columnar (absorptive) cells, goblet cells and intraepithelial leucocytes. The epithelium from normal animals was significantly taller than GnRH-treated samples. Conventional histochemistry displayed the same staining pattern in normal and hormone-treated specimens which showed a mixture of neutral and sulphated acidic glycoconjugates in the luminal surface and goblet cells, and neutral glycans in apical granules of enterocytes. Lectin histochemistry revealed a different glycoconjugate pattern in normal and GnRH-treated tunas. In normal specimens the luminal surface expressed sialoglycoconjugates which bound MAL II, SNA, KOH-sialidase-PNA, KOH-sialidase-SBA as well as asialoglycans stained with HPA, SBA, GSA I-B4 , LTA. N-linked glycans were highlighted by Con A and KOH-sialidase-WGA. In GnRH-treated tunas the luminal surface did not react with SNA, SBA and LTA. The columnar cells of normal tunas bound KOH-sialisase-PNA in the apical region, KOH-sialidase-PNA, KOH-sialidase-DBA, HPA, SBA, KOH-sialidase-SBA and KOH-sialidase-WGA in apical granules, GSA I-B₄ and LTA in the supranuclear region. GnRH-treated specimens showed some columnar cells that stained with KOH-sialidase-WGA in the apical granules and with GSA I-B4 in the supranuclear region. The goblet cells of normal animals produced mucins positive to PNA, HPA, KOH-sialidase-DBA, SBA, GSA II. The latter three binding sites lacked in GnRH-treated tunas. The results suggest that the mucosal epithelium of Thunnus thynnus L. pyloric caeca expresses a complex glycan pattern that is affected by GnRH-treatment.

Effects of colchicine on localization of alkaline phosphatase in McA-RH 7777 rat hepatoma cells

We investigated the changes caused by microtubule disruption in cell contact-induced translocation of alkaline phosphatase (ALP) from the Golgi area to the plasma membrane in McA-RH 7777 cells. When the cells were treated with colchicine, the tubular structure of microtubules in the cytoplasm was lost. Colchicine treatment also resulted in the appearance of numerous dots containing mannosidase II (man II) throughout the cytoplasm. Moreover, ALP was distributed in small dots throughout the cytoplasm, as well as in all regions of the plasma membrane, although it was most concentrated at sites of intercellular contact. On the other hand, when the cells were incubated in basal medium after colchicine treatment, large spots containing ALP reappeared in the perinuclear cytoplasm more quickly than the accumulation of small dots containing man II. These findings suggest that colchicine causes disassembly of the Golgi complex into fragments, which scatter throughout the cytoplasm, but that it does not interfere with translocation of ALP to the plasma membrane. Furthermore, cytoplasmic ALP may be localized at sites other than the Golgi complex.

Glycocomposition of the apocrine interdigital gland secretions in the fallow deer (Dama dama)

The secretions of the tubular interdigital glands were investigated by conventional (Periodic-Acid Schiff, Alcian-Blue at different pH, Low Iron Diamine and High Iron Diamine) and lectin (Con-A, UEA-I, LTA, WGA, GSA-II, GSA-IB4, SBA, PNA, ECA, DBA, MAL-II and SNA) histochemical methods in adult males and females of different age of fallow deer during the breeding season. Sialidase digestion and deacetylation pre-treatment were also employed in conjunction with lectin histochemistry. The glandular epithelium consisted of a single layer of low columnar cells with typical apical protrusions. No substantial differences of the above histochemical staining in relation to sex and age were observed. Conventional histochemical staining revealed that the interdigital glands secreted neutral glycoproteins whereas acidic glycocomponents did not seem to be present. Lectin histochemical technique allowed us to disclose a great heterogeneity of glycoproteins with N- and O-linked oligosaccharides containing alpha-d-Man/alpha-d-Glc, GlcNAc, alpha-Fuc, terminal beta-d-Gal-(1-3)-d-GalNAc, -d-Gal-(1-4)-d-GlcNAc, alpha-Gal and beta-GalNAc residues. beta-GalNAc and disaccharide beta-d-Gal-(1-3)-d-GalNAc were also found as subterminal to sialyl moieties. The lack of sexual and age-related differences in the glucidic content of the glandular secretions seems to indicate that the glycoderivatives may play only an accessory role in the production of odoriferous signals in fallow deer.

Terminal Glycosylation in Human Cervical Mucin

L-Fucose and N-acetylneuraminic (sialic) acid occupy terminal positions on the oligosaccharide side-chains of human cervical mucin but the addition of both these monosaccharides to the same carbohydrate acceptor residue is kinetically unfavourable. The following evidence suggests that the levels of L-fucose are more sensitive to regulation than those of N-acetylneuraminic acid: (1) tissue levels of sialyltransferase (EC 2.4.99.1) activity are 20-30 times greater than those of fucosyltransferase (EC 2.4.1.68); (2) both glycosyltransferases are susceptible to inhibition by their nucleotide products but a comparison of the Ki and the apparent Km of these enzymes shows that modulation of fucosyltransferase is more probable; (3) Postsecretory removal of L-fucose from cervical mucin is probably due to the high levels of mucus-associated alpha-L-fucosidase. Furthermore the activity of this enzyme is probably modulated by the pH gradient within the cervix. Mucin glycosylation can be visualized by autoradiography using [3H]L-fucose applied to cervical explants in organ culture. Mucus production during this process is not sensitive to exogenous ovarian steroid hormones, though in other aspects the secretory process appears normal. It is proposed that the cyclicity of mucus rheology is not directly influenced by an action of these hormones on mucin synthesis or hydration.

Biosynthesis and transport of plasma membrane glycoproteins in the rat intestinal epithelial cell: studies with sucrase-isomaltase

Sucrase-isomaltase (SI), an integral heterodimeric glycoprotein of the intestinal microvillus membrane, is synthesized as a single enzymically active precursor protein (pro-SI) of high relative molecular mass. After glycosylation in the Golgi complex pro-SI is transferred to the microvillus membrane where it is cleaved into the two subunits by pancreatic elastase. Pro-SI was purified by monoclonal antibody-affinity chromatography from microvillus membranes of fetal intestinal transplants in which SI is found exclusively in the non-cleaved precursor form. The N-terminal amino acid sequence of pro-SI was identical to that of the isomaltase subunit of SI which anchors the mature enzyme complex to the lipid bilayer, but it differed from the N-terminal sequence of the sucrase subunit of SI. This structural comparison indirectly gave insight into the mechanisms of membrane insertion and assembly of pro-SI during its biosynthesis. Subcellular fractionation studies indicate transient structural association of newly synthesized pro-SI with the basolateral membrane on its transfer from the Golgi complex to the microvillus membrane, suggesting that part of the basolateral membrane or its associated structures might be involved in the sorting-out processes of microvillar membrane proteins. This concept may have general relevance for the mechanisms of membrane insertion, intracellular transport and sorting of other microvillar membrane glycoproteins in the intestinal epithelial cell.

Proteinases release mucin from airways goblet cells

The mucin-release effect of proteinases on airways epithelium was assessed in vitro. Using explants of rabbit tracheal mucosa-submucosa we determined that elastase and alkaline proteinase from Pseudomonas aeruginosa, pancreatic trypsin and elastase and the microbial proteinases subtilisin, thermolysin and pronase, all stimulate mucin release from goblet cells. On the other hand Streptomyces caespitosus proteinase pancreatic chymotrypsin and collagenase fail to trigger mucin release. Bovine trachea and human nasal polyp epithelium also release mucins in response to proteinases. Mucin release activity is dependent on proteolytic activity of enzymes which have a fairly broad, but generally similar, substrate specificity. The cellular mechanism of action is not known. We propose that mucin secretion in response to proteinases represents a useful defence mechanism but also forms the basis for hypersecretory states and airways obstruction in chronic endobronchial inflammatory states.

Change in localization of alkaline phosphatase and mannosidase II by colchicine treatment of primary cultures of fetal rat hepatocytes

We examined the changes in localization of alkaline phosphatase (ALP) and mannosidase II (man II), a Golgi marker, after colchicine treatment of primary cultures of fetal rat hepatocytes, using double immunofluorescence staining and confocal laser microscopy. In hepatocytes cultured in basal medium, ALP was localized in the perinuclear cytoplasm, and man II was observed in the Golgi region of the cytoplasm. When hepatocytes were cultured in dexamethasone-supplemented medium, ALP was also localized in the plasma membrane surrounding the bile canaliculus-like structure that was formed between adjacent cells. In hepatocytes cultured in the same medium containing colchicine, the structure of microtubules in the cytoplasm was lost, man II exhibited granular distribution scattering throughout the cytoplasm, and ALP was localized in coarse granular sites of the cytoplasm. However, ALP was not colocalized at the same sites as man II. The present study indicated that colchicine inhibits the dexamethasone-promoted translocation of ALP to the plasma membrane surrounding the bile canaliculus-like structure in primary cultures of fetal rat hepatocytes by disassembling microtubules and discomposing the Golgi complex.

X-ray microanalysis of biological specimens by high voltage electron microscopy

For the purpose of analyzing and imaging chemical components of cells and tissues at the electron microscopic level, 3 fundamental methods are available, chemical, physical and biological. Among the physical methods, two methods qualifying and quantifying the elements in the structural components are very often employed. The first method is radioautography which can demonstrate the localization of radiolabeled compounds which were incorporated into cells and tissues after the administration of radiolabeled compounds. The second method is X-ray microanalysis which can qualitatively analyze and quantify the total amounts of elements present in cells and tissues. We have developed the two methodologies in combination with intermediate high or high voltage transmission electron microscopy (200-400 kV) and applied them to various kinds of organic and inorganic compounds present in biological materials. As for the first method, radioautography, I had already contributed a chapter to PHC (37/2). To the contrary, this review deals with another method, X-ray microanalysis, using semi-thin sections and intermediate high voltage electron microscopy developed in our laboratory. X-ray microanalysis is a useful method to qualify and quantify basic elements in biological specimens. We first quantified the end-products of histochemical reactions such as Ag in radioautographs, Ce in phosphatase reaction and Au in colloidal gold immunostaining using semithin sections and quantified the reaction products observing by intermediate high voltage transmission electron microscopy at accelerating voltages from 100 to 400 kV. The P/B ratios of all the end products Ag, Ce and Au increased with the increase of the accelerating voltages from 100 to 400 kV. Then we analyzed various trace elements such as Zn, Ca, S and Cl which originally existed in cytoplasmic matrix or cell organelles of various cells, or such elements as Al which was absorbed into cells and tissues after oral administration, using both conventional chemical fixation and cryo-fixation followed by cryo-sectioning and freeze-drying, or freeze-substitution and dry-sectioning, or freeze-drying and dry-sectioning producing semithin sections similarly to radioautography. As the results, some trace elements which originally existed in cytoplasmic matrix or cell organelles of various cells in different organs such as Zn, Ca, S and Cl, were effectively detected. Zn was demonstrated in Paneth cell granules of mouse intestines and its P/B ratios showed a peak at 300 kV. Ca was found in human ligaments and rat mast cells with a maximum of P/B ratios at 350 kV. S and Cl were detected in mouse colonic goblet cells with maxima of P/B ratios at 300 kV. On the other hand, some elements which were absorbed by experimental administration into various cells and tissues in various organs, such as Al in lysosomes of hepatocytes and uriniferous tubule cells in mice was detected with a maximum of P/B ratios at 300 kV. From the results, it was shown that X-ray microanalysis using semi-thin sections observed by intermediate high voltage transmission electron microscopy at 300-400 kV was very useful resulting in high P/B ratios for quantifying some trace elements in biological specimens. These methodologies should be utilized in microanalysis of various compounds and elements in various cells and tissues in various organs.

Glucidic determinants expressed by the digestive apparatus of Umbrina cirrosa (L.) fries as revealed by lectin histochemistry

Glycoconjugates present in the various parts of the digestive apparatus (oesophagus, stomach, intestine) of 27, 34 and 44 days-old Umbrina cirrosa (L.) fries were characterised by means of lectin histochemistry in conjunction with sialidase digestion and KOH treatment. High amounts of carbohydrates were detected especially in goblet cells of the oesophagus. Positivity obtained with the various lectins in oesophagus, stomach and intestine did not change during the development of the fries examined. D-Gal and D-GalNAc appeared to occupy a terminal position in oligosaccharidic chains whereas they are linked to sialic acid residues in adult subjects, which suggests an incomplete chemical structure of the glycoconjugates secreted by the digestive apparatus of fries.

Ultrastructural changes in the vas deferens of langur monkeys Presbytis entellus entellus after vas occlusion with styrene maleic anhydride and after its reversal

Ultrastructural changes in the vas deferens of langur monkeys after 150 days of vas occlusion with styrene maleic anhydride (SMA) and after 150 days of noninvasive reversal are reported. The vas deferens of the sham-operated control animals revealed active secretory and absorptive functions. The basal cells showed prominent nucleus and sparse cytoplasmic organelles, and the principal cells characterized by oval or irregular nucleus, well developed mitochondria, Golgi bodies, rough endoplasmic reticulum, secretory granules in the Golgi area, free ribosomes, and glycogen granules in the supranuclear region suggesting secretory function. Vesicles and stereocilia in the apex region suggested absorptive functions of the vas deferens. Vas occlusion by SMA resulted in exfoliation of epithelial cells, pyknotic nuclei, and vacuolated cytoplasm virtually devoid of cytoplasmic organelles and stereocilia. After noninvasive reversal, the vas epithelium regained a state of normalcy as evidenced by prominent plasma membrane, nucleus, cytoplasmic organelles, and stereocilia. The results suggest that the exfoliation of the epithelium due to vas occlusion by SMA regains normalcy after 150 days of noninvasive reversal.

Radioactive fucose as a tool for studying glycoprotein secretion

The efficiency and reliability of radioactive fucose as a specific label for newly synthesized glycoproteins were investigated. Young adult male rabbits were injected intravitreally with [3H]-fucose, [3H]-galactose. [3H]-mannose, N-acetyl-[3H]-glucosamine or N-acetyl-[3H]-mannosamine, and killed 40 h after injection. In another series of experiments rabbits were injected with either [3H]-fucose or several tritiated amino acids and the specific activity of the vitreous proteins was determined. Vitreous samples were also processed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and histological sections of retina, ciliary body and lens (the eye components around the vitreous body) were processed for radioautography. The specific activity (counts per minute per microgram of protein) of the glycoproteins labeled with [3H]-fucose was always much higher than that of the proteins labeled with any of the other monosaccharides or any of the amino acids. There was a good correlation between the specific activity of the proteins labeled by any of the above precursors and the density of the vitreous protein bands detected by fluorography. This was also true for the silver grain density on the radioautographs of the histological sections of retina, ciliary body and lens. The contribution of radioautography (after [3H]-fucose administration) to the elucidation of the biogenesis of lysosomal and membrane glycoproteins and to the determination of the intracellular process of protein secretion was reviewed. Radioactive fucose is the precursor of choice for studying glycoprotein secretion because it is specific, efficient and practical for this purpose.

Detection of sugar residues in rabbit embryo teeth with lectin-horseradish peroxidase conjugate: II. A light microscopal study

The cellular distribution and changes of sugar residues during tooth development in embryos of the rabbit Oryctolagus cuniculus were investigated by using horseradish peroxidase-conjugated lectins (lectin-HRP). The lectins SBA, ECA, and LTA show no binding to any region of the dental cap and bell stages, whereas BS-1 and UEA-1 bind to dental cells at both stages. Appropriate control studies confirmed the specificity of the binding of the lectins. At cap stage, the lectins BS-1 and UEA-1 show moderate binding to the (pre)-ameloblast and (pre)-odontoblast cells. These results suggest that the acetylgalactosamine and alpha-L-fucose residues present in (pre)-ameloblasts and (pre)-odontoblasts, respectively, are common to determined but relatively undifferentiated cells capable of forming matrices of hard tissues. Since the odontoblast and ameloblast express dentin and enamel, respectively, it can be speculated that the abundance of these residues in these cells might be associated with the maintenance of the capacity of the cells to produce such matrices. At the bell stage, the odontoblasts display considerable amounts of alpha-L-fucose, whereas alpha-L-fucose is poorly localized in ameloblasts. However, ameloblasts contain significant quantities of N-acetylgalactosamine, whereas only a diffuse positivity for this carbohydrate is apparent in odontoblasts. The marked changes of the glycosylation pattern of these glycoconjugates might indicate that they play a role during the cell-to-cell interaction and might also be involved in the odontoblastic and ameloblastic functional activity. Such a possibility is entirely speculative until specific in vitro experiments are conducted.

Light microscopic detection of sugar residues in rabbit embryo teeth with lectin-horseradish peroxidase conjugates

We investigated the binding of five HRP-conjugated lectins to rabbit tooth germs at the cap and late bell stages of development. The results revealed some changes in the glycosylation patterns of the glycoconjugates. Sugar residues, such as alpha-D-mannose, methyl-D-glucose, N-acetylglucosamine, beta-D-galactosamine, D-galactose, and sialic acid, were detectable in some components of the tooth germs. The most conspicuous developmental change was increased binding of Con A and WGA. These lectins showed, at the cap stage, moderate binding to the (pre)-ameloblasts and (pre)-odontoblasts. With further development to the late bell stage, but prior to the achievement of well-defined morphological-functional characteristics, the odontoblasts and ameloblasts displayed considerable amounts of alpha-D-mannose, alpha-D-glucose as well as beta-D-acetylglucosamine and sialic acid. Appropriate control studies confirmed the specificity of the binding of the lectins. Two lectins (DBA and PNA) with known specificity for N-acetylgalactosamine groups were bound by the basement membranes in tooth germs at the cap stage. A third lectin (RCA) with the same specificity did not produce any detectable staining in the same material. Further studies must be planned to determine the specific functions and significance of lectin-HRP-binding glycoconjugates in odontogenesis.

Freeze-fracture study of cell junctions in the epididymis and vas deferens of a seasonal breeder: the mink (Mustela vison)

The present study used the freeze-fracture technique and vascular infusion of horseradish peroxidase (HRP) as a junction permeability tracer, visible in thin sections, to investigate potential seasonal variations in the mink epididymis and vas deferens cell junctions. The junctions were studied in kits during the neonatal period, during and after puberty, and during adulthood monthly throughout the annual reproductive cycle. Results showed the existence, at the time of birth, of a junctional complex joining ductal cells that reached the lumen of the epididymis and vas deferens. The lumenal impermeable segment of the junctional complex was characterized by the presence of an occluding zonule made up of continuous tight junctional ridges extending around the perimeter of the cell. The basal permeable segment of the junctional complex contained mainly discontinuous ridges with frequent forming gap and tight junctions next to adhering junctions. Receding annular junctions were present in the apical and lateral cytoplasm of principal and clear cells. The membrane domain apical to the occluding zonule bore 30-35 nm exo/endocytosis blebs and 40-60 crenations associated with deforming tight and gap junctions made up of randomly scattered particles. Patterns of junctional strands varied greatly from one principal and/or clear cell to another. However, cell junctions did not significantly vary from the neonatal period to adulthood nor from breeding to testicular regression. Anatomical subdivisions of the epididymis with fewer junctional strands per zonule and high diversity in their patterns exhibit no permeability differences to HRP when compared with subdivisions containing more numerous strands. The junctions were impermeable during the neonatal period and throughout the annual reproductive cycle. The following conclusions were reached: 1) a competent occluding zonule developed in the mink epididymis and vas deferens before it did in the testis; 2) the number of strands and the diversity of patterns did not correlate with permeability differences; 3) after the development of a lumen in the testicular excurrent duct, neither receding cellular changes caused by testicular regression nor seasonal passage of a bolus of sperm through the duct modified the occluding zonules; and 4) in the testicular excurrent duct, junction modulation (i.e., formation and deformation) paralleled that in the testis and followed the direction of the synthesis-transport-secretion process.

Insulin-binding sites in the mouse deferent duct

In vivo light microscopic autoradiography was used to demonstrate the presence of specific insulin-binding sites in the mouse deferent duct three min after intravenous injection of 125I-insulin with or without excess of unlabeled insulin. The studies showed high specific insulin binding in the endothelial cells of capillaries and certain fibroblasts of the lamina propria. In the epithelium, although the tall columnar cells were free of specific insulin binding, the basal cells had relatively high specific insulin binding. Because the deferent duct has been considered to exert certain effects on sperms, the presence of high specific insulin binding at these sites may provide further support for this concept.

Oat bran, rye bran, and soybean hull increase goblet cell volume density in the small intestine of the golden hamster. A histochemical and stereologic light-microscopic study

Small-intestinal morphology, particularly the amount of goblet cells, was studied in Syrian golden hamsters fed either a low-fibre (0.5% fibre) diet or the same diet supplemented with oat bran, rye bran, or soybean hull (12% fibre) during 6 weeks. All fibre diets increased the density of goblet cell volume to epithelial volume and to villus volume in the ileum and to some extent in the jejunum and also the number of goblet cells related to surface traces of villi both in the proximal and distal small intestine. The weight of the small intestine and the circumference and the volume of the intestinal wall in the ileum were greater in the rye bran diet group as compared with all the other groups, suggesting hyperplasia. These results suggest that oat bran, rye bran, and soybean hull supplementation might result in higher goblet cell secretory activity in both the proximal and distal small intestine of hamsters. The various fibre sources influenced the small-intestinal wall differently.

Use of compounds naturally labeled with stable isotopes for the study of the metabolism of glycoprotein neutral sugars by gas-liquid chromatography-isotope-ratio mass spectrometry. Technical validation in the rat

In order to develop an alternative method to radioactive labeling for the study of the glycoprotein sugar metabolism in man, the possible use of stable isotopes provided by naturally, 13C-enriched dietary compounds has been explored in rat intestine and serum. Rats were fed a semisynthetic diet containing 67% wheat starch (containing 1.08692 13C atom/100 carbon atoms) for a week, and then the same diet containing corn starch (1.10042% 13C) for a week. Neutral sugars were prepared from delipidated, trichloroacetic acid-precipitable material from 200-400 mg of intestinal mucosa or 1 mL of serum, separated, and analyzed as alditol acetates by gas-liquid chromatography coupled to isotope-ratio mass spectrometry. This technique allowed the determination, in a single experiment, of the amount and 13C abundance of six neutral sugars (including xylose used as internal standard). Despite the low abundance of 13C in natural products, the sensitivity of the technique was found to be sufficient to detect isotopic enrichment as low as 0.001% with good accuracy and reproducibility in 2 micrograms of each glycoprotein neutral sugar. As an example, the pattern of labeling by dietary D-glucose from corn starch appears to be very different for fucose, ribose, mannose, galactose, and glucose of intestine or serum macromolecules.

Structural differentiation of the epithelial cells of the testicular excurrent duct system of rats during postnatal development

The light and electron microscopic appearance of the various epithelial cells lining the efferent ducts and different regions of the epididymis were examined in rats on postnatal days 21, 39, 49, 56, and 90 to determine the role of androgens and/or spermatozoa, as well as other possible factors, on the structural differentiation of these cells. Five conclusions may be drawn from the observations made. First, on day 21 epithelial cells of all regions are structurally undifferentiated. Second, it was not until day 49 that nonciliated cells of the efferent ducts resembled those of adult animals, suggesting that more than one factor, such as androgens, testicular products, and/or spermatozoa, is needed for their full structural differentiation. Third, principal cells of the epididymis become structurally differentiated by day 39, i.e., these cells contained an elaborate Golgi apparatus, endoplasmic reticulum cisternae, and numerous 200-400 nm electron lucent secretory vesicles, as well as a full complement of endocytic organelles; this occurred in spite of the absence of spermatozoa in the epididymal lumen. The differentiation of these epididymal cells may be under the influence of androgens, which are known to be high at this time, but may also be due to specific secretions from Sertoli cells secreted directly into the efferent ducts. Fourth, clear cells of the cauda epididymidis are fully differentiated by day 39. The presence of degenerating germ cells in the lumen of the cauda epididymidis and various cellular debris, as well as high androgen levels, may be factors causing the differentiation of the cells of this region. Finally, clear cells of the corpus and cauda epididymidis only become fully differentiated by day 49, at a time when spermatozoa appear in the lumen, despite high levels of androgens at day 39; this observation indicates that the presence of spermatozoa in the lumen may be a necessary factor in causing their differentiation. Overall, these results suggest that a combination of different factors are necessary for the structural differentiation of the various epithelial cell types of the different regions of the epididymis.

Autoradiographic, electrophoretic, and immunocytochemical studies of glycoproteins of the rabbit iris

L-[3H]fucose was injected either intravitreally or intra-aqueously into adult rabbits which were killed at several time points after injection. SDS-polyacrylamide gel electrophoresis and fluorography of iris extracts revealed that most of the proteins are glycoproteins containing fucose residues. Autoradiography of semi-thin histologic sections demonstrated that glycoprotein synthesis was most prominent in the epithelium of the iris, while little protein synthesis was evident in the stroma of the iris. The results of these experiments indicated that the glycoproteins of the iris undergo renewal. The protein band pattern of the iris extracts was very similar to that of extracts of the ciliary body. The high-molecular-weight cartilage matrix glycoprotein (CMGP), an intrinsic component of the ciliary body, vitreous, and aqueous humor, was detected by immunohistologic studies only in the stroma of the iris. The results of immunohistochemical analyses of the eyes of young rabbits (1-21 days old), in addition to the autoradiographic findings, strongly suggest that CMGP is not an intrinsic glycoprotein of the iris stroma, at least in this species.

Rat small intestinal mucins: a quantitative analysis

Although much is known about the qualitative distribution of mucin-secreting goblet cells in the small intestine, the quantitative distribution of stored mucins remains undefined. The purpose of this study was to determine the distribution of neutral stored mucin in the rat small intestine by using morphometric techniques and once established, to verify that this methodology could detect secretion in animals exposed to a known mucin secretagogue. Twelve male Wistar rats (five baseline, five pilocarpine-treated, and two vehicle controls) were fixed by vascular perfusion. After a brief fixation the intestine was removed, cut into 10 equal segments, sliced, and fixed overnight. Methacrylate sections from each segment were stained with periodic acid-Schiff and toluidine blue. For morphometry, the volume of epithelium per surface area of epithelial basal lamina was calculated with a Merz grid. The volume density of stored mucin per epithelium was determined by point-counting on a square lattice grid. Volumes were related to either surface area of epithelial basal lamina or mucosal surface area. Due mostly to contributions by villus stored mucin, the total amount of product was found to increase proximally to distally in the small bowel, with the most dramatic increases occurring in the first three segments. When subjected to pilocarpine, a massive secretory response was evoked, resulting in a near total depletion of crypt stored mucin at all levels of the small bowel. Secretion of villus stored mucin also occurred throughout the small intestine, however reaching levels of significance at only a few points. This study describes the distribution of stored mucin in the small intestine under baseline and accelerated secretory conditions.

Subcompartment sugar residues of gastric surface mucous cells studied with labeled lectins

We examined the intracellular localization of sugar residues of the rat gastric surface mucous cells in relation to the functional polarity of the cell organellae using preembedding method with several lectins. In the surface mucous cells, the nuclear envelope and rough endoplasmic reticulum (rER) and cis cisternae of the Golgi stacks were intensely stained with Maclura pomifera (MPA), which is specific to alpha-Gal and GalNAc residues. In the Golgi apparatus, one or two cis side cisternae were stained with MPA and Dolichos biflorus (DBA) which is specific to terminal alpha-N-acetylgalactosamine residues, while the intermediate lamellae were intensely labeled with Arachis hypogaea (PNA) which is specific to Gal beta 1,3 GalNAc. Cisternae of the trans Golgi region were also stained with MPA, Ricinus communis I (RCA I) which is specific to beta-Gal and Limax flavus (LFA) which is specific to alpha-NeuAc. Immature mucous granules which are contiguous with the trans Golgi lamellae were weakly stained with RCA I, while LFA stained both immature and mature granules. The differences between each lectin's reactivity in the rough endoplasmic reticulum, in each compartment of the Golgi lamellae and in the secretory granules suggest that there are compositional and structural differences between the glycoconjugates in the respective cell organellae, reflecting the various processes of glycosylation in the gastric surface mucous cells.

Alterations in rat intestinal mucin patterns following luminal infusion of acetylsalicylic acid and prostaglandin derivatives

The secretion of gastrointestinal mucin and/or the formation of mucoid caps have been implicated in cytoprotective or repair mechanisms related to mucosal injury models. In this study, rats were treated with acetylsalicylic acid (ASA) or prostaglandins (PG), and their effects on the synthesis and secretion of small intestinal mucin were examined. A newly developed polyclonal antibody to rat intestinal mucin was used for immunoassay of rat intestinal luminal and tissue mucin. The mucin antigen source was obtained by vacuum aspiration of luminal mucus. A high-molecular-weight glycoprotein (2 x 10(6) Da) fraction injected into rabbits produced a primary mucin antibody. A sensitive and quantitative enzyme-linked immunosorbent assay (ELISA) was developed that yielded a highly reproducible and linear response with mucin aliquots containing 0-20 ng of protein/ml. Incorporation of the plasma tracers ([3H]glucose and [35S]sodium sulfate) into mucin derived from hexadecyltrimethylammonium bromide precipitation after treatment with ASA (100 mg/kg body wt) decreased, although administration of dimethylprostaglandin E2 (100 micrograms/kg body wt) significantly increased the specific tracer incorporation values for the sialomucin and sulfomucin indices in luminal mucin fractions. The immunoassay data pattern for the ELISA technique was virtually identical to the results of the radiolabeled tracer method obtained for the same pharmacologic treatments. These experiments demonstrate that the estimation of synthesized mucin (tissue source) or secreted mucin (luminal source) as determined by the ELISA technique is similar to that obtained by the time-consuming and labor-intensive tracer incorporation methodology.

Changes in vasoactive intestinal polypeptide (VIP) levels in the rabbit oviduct at different hormonal stages. An immunohistochemical study

In this study we investigated immunohistochemically the distribution of VIP in ampullary and isthmic segments of the rabbit oviduct at different hormonal stages in order to correlate the presence of VIP with the morphological and functional differences between the two oviduct segments. Noticeable changes in the VIP-positive sites emerged between corresponding oviduct segments during the stages examined. A reduction in VIP presence was noted in oestrus and the lowest VIP values occurred one and three days after mating in the ampulla and the isthmus respectively. In the subsequent stages an increase of VIP was noted in both tracts which showed features comparable to that described in anoestrus. The levels and distribution of VIP is correlated with the functions of the oviduct segments concerned with egg transport and formation of a mucopolysaccharide envelope around blastocysts.

Characterization of the synthetic capacities of isolated placental binucleate cells from sheep and goats

Sheep and goat binucleate cells (BNC) play a central role in placental growth and development. This study reports a simple method for isolating 60-70% pure populations of BNC of high viability. After incubation of the isolated BNC with a brief pulse of 14C-leucine or 3H-fucose or 3H-galactose, electron microscope autoradiography showed that label was eventually incorporated into the characteristic BNC granules via the Golgi body. Fucose and galactose initially showed a much higher Golgi body label than leucine, which was at first predominantly localised in the endoplasmic reticulum. 35S-methionine incorporation by BNC suspensions was extensive enough to allow an immunoprecipitation investigation which demonstrated that the protein hormone ovine placental lactogen and the SBU-3 antigen were synthesised de novo. Previous studies with isolated BNC have shown a remarkable range of substances to be released into the incubation medium but not necessarily synthesised during the incubation. The results demonstrate unequivocally that isolated BNC's are capable of total synthesis in vitro of two of the proteins that these same cells are known to secrete in vivo.

Cycle- and function-related changes in lectin binding to human endometrium: a histochemical study with pronase treatment

Forty-eight endometrial biopsy specimens were obtained during a normal menstrual cycle, during pregnancy and from patients with dysfunctional bleeding. The specimens were examined for Peanut (PNA), Soybean (SBA), Vicia villosa (VVA), Phytohem- (PHA), Lens culinaris (LCA) and Concanavalin (succ. Con A) agglutinin binding. The study was performed on paraffin sections using the pronase digestion and either the peroxidase-antiperoxidase or the avidin-biotin-peroxidase method. Cycle-related changes of the PNA, SBA, VVA, and to some degree PHA binding, were based on the transfer of the cytoplasmic reaction toward the glandular lumena. PNA + and SBA + material moved to the cell surface at the transition of the follicular and luteal phase and before the basal vacuolization appeared. Functional disturbances mainly influenced the intensity of the reaction. It was true only for those lectins, whose binding pattern showed cycle-related changes. In curettings from patients with a prolonged menstrual cycle the lectin binding seen in normal late secretory endometrium was absent or significantly diminished. Lectin binding to the endometrial surface epithelium was variable; PHA was the only lectin, the binding pattern of which followed cyclic changes in the glycocalyx, detected previously by means of PAS and alcian blue methods.

Use of transgenic mice to study the routing of secretory proteins in intestinal epithelial cells: analysis of human growth hormone compartmentalization as a function of cell type and differentiation

The intestinal epithelium is a heterogeneous cell monolayer that undergoes continuous renewal and differentiation along the crypt-villus axis. We have used transgenic mice to examine the compartmentalization of a regulated endocrine secretory protein, human growth hormone (hGH), in the four exocrine cells of the mouse intestinal epithelium (Paneth cells, intermediate cells, typical goblet cells, and granular goblet cells), as well as in its enteroendocrine and absorptive (enterocyte) cell populations. Nucleotides -596 to +21 of the rat liver fatty acid binding protein gene, when linked to the hGH gene (beginning at nucleotide +3) direct efficient synthesis of hGH in the gastrointestinal epithelium of transgenic animals (Sweetser, D. A., D. W. McKeel, E. F. Birkenmeier, P. C. Hoppe, and J. I. Gordon. 1988. Genes & Dev. 2:1318-1332). This provides a powerful in vivo model for analyzing protein sorting in diverse, differentiating, and polarized epithelial cells. Using EM immunocytochemical techniques, we demonstrated that this foreign polypeptide hormone entered the regulated basal granules of enteroendocrine cells as well as the apical secretory granules of exocrine Paneth cells, intermediate cells, and granular goblet cells. This suggests that common signals are recognized by the "sorting mechanisms" in regulated endocrine and exocrine cells. hGH was targeted to the electron-dense cores of secretory granules in granular goblet and intermediate cells, along with endogenous cell products. Thus, this polypeptide hormone contains domains that promote its segregation within certain exocrine granules. No expression of hGH was noted in typical goblet cells, suggesting that differences exist in the regulatory environments of granular and typical goblet cells. In enterocytes, hGH accumulated in dense-core granules located near apical and lateral cell surfaces, raising the possibility that these cells, which are known to conduct constitutive vesicular transport toward both apical and basolateral surfaces, also contain a previously unrecognized regulated pathway. Together our studies indicate that transgenic mice represent a valuable system for analyzing trafficking pathways and sorting mechanisms of secretory proteins in vivo.

Intracellular transport and neuronal activation of phospholipid and glycoprotein synthesis during axonal regeneration of cranio-spinal nerves

In the present work, the hypothesis that the increased rapid intracellular transport of newly-synthesized material along the axons of a regenerating system is sustained by an alteration of the transport of proteolipid complexes through subcellular compartments of a neuronal cell body was tested by a biochemical methodology. The motoneurons of spinal cord ventral horn, 4 wk after unilateral lesion (crush) of cervico-thoracic nerves of the rabbit at the level of brachial plexus, were chosen as the model system of regeneration. A time-staggered procedure of in vivo and in vitro double labeling with metabolic precursors, such as [3H]-choline, [14C]-choline, [3H]-fucose, and [14C]-fucose, was used. Subcellular fractions (RER, SER, Golgi apparatus, and plasma membranes) of ventral horn tissue, taken from spinal cord hemisections (regenerating and contralateral side), were further isolated. Twenty-eight days after axotomy, we did not observe any change of intracellular transport kinetics (14C/3H ratio) of newly-synthesized choline-phospholipids and glycoproteins in regenerating motoneurons compared to controls. However, associated with regenerating phenomenon in Golgi apparatus, we observed an increase of labeled choline-phospholipid and glycoprotein material that could contribute to the increased fast axonal transport and delivery of membrane proteolipid complexes to plasma membrane and axonal compartments. The increase of glycoprotein labeling was more pronounced in the SER portion (vesicles and elements of smooth membranes). This result is in favor of the hypothesis that membrane-bound proteins are transported from the Golgi to the axon through the perikaryal SER.

Characterization of fucosyltransferase activity during mouse spermatogenesis: evidence for a cell surface fucosyltransferase

Fucosyltransferase activity was quantified in mouse germ cells at different stages of spermatogenesis. Specifically, fucosyltransferase activities of pachytene spermatocytes, round spermatids, and cauda epididymal sperm were compared. Fucosyltransferase activity of mixed germ cells displayed an apparent Vmax of 17 pmol (mg of protein)-1 min-1 and an apparent Km of approximately 13 microM for GDP-L-[14C]fucose in the presence of saturating amounts of asialofetuin at 33 degrees C. Under these conditions, cellular fucosyltransferase activity was found to increase during spermatogenesis. In agreement with assays of intact cells, examination of subcellular fractions indicated that a large fraction of fucosyltransferase activity was associated with the cell surface. The fraction of fucosyltransferase activity that was associated with the cell surface progressively increased throughout spermatogenesis and epididymal maturation so that nearly all of the fucosyltransferase in epididymal sperm was on the cell surface. Specifically, by comparison of activities in the presence and absence of the detergent NP-40, the fraction of fucosyltransferase activity that was associated with the cell surface in pachytene spermatocytes, round spermatids, and epididymal sperm was 0.36, 0.5, and 0.85, respectively. These results suggest that a cell surface fucosyltransferase may be important during differentiation of spermatogenic cells in the testis as well as during epididymal maturation and fertilization.

Lectin histochemistry of the embryonic heart: fucose-specific lectin binding sites in developing rats and chicks

Glycoconjugates, particularly their sugar side chains, play important roles in embryonic development. Changes in cell-surface-associated glycoconjugates are known to affect cell differentiation, cellular interactions, and other developmental phenomena during embryogenesis. The embryonic heart goes through a series of complicated morphologic events during development. Of particular interest is morphogenesis of the outflow tract. This region of the embryonic heart originates from more than one cell population and undergoes a complex process of septation during formation of the great vessels. Histochemical analysis with a series of fucose-specific lectins conjugated to horseradish peroxidase has revealed the presence of a fucosylated glycoconjugate in the outflow tract of the developing heart. The results reveal further that the expression of the fucosylated glycoconjugate is stage-dependent and thus probably genetically regulated. The timing and distribution of staining with the lectin OFA suggest that this fucosylated glycoconjugate may play a role in directing the migration of neural crest cells into the heart and subsequent formation of the conus septum.

Histochemical and radioautographic study of glycoprotein secretion in the epithelium lining the uterine tubes of mice

Two-month-old female Swiss mice that had come into estrus were injected intravenously with L-3H-fucose and killed at 5, 15, 40 min, and 4 h after injection. Pieces of the isthmus and of the ampulla of the uterine tubes were processed for light- and electron-microscopic radioautography. Incorporation of 3H-fucose was more intense in the isthmian secretory cells than in the ciliated cells of the ampulla. Electron-microscopic radioautography of the isthmian secretory cells demonstrated that 3H-fucose was incorporated into newly synthesized glycoproteins in the Golgi apparatus from where labelled glycoproteins migrated mainly to secretory granules and apical microvilli. The histochemical technique using ruthenium red confirmed the presence of glycoproteins in the contents of the secretory granules released to the lumen of the uterine tubes as demonstrated by radioautography. Other glycoproteins are transported inside small vesicles and most likely are related to the renewal of the plasma membrane. The role of the secretory glycoproteins in various events of mammalian reproduction is discussed.

Role of cytoplasmic vacuoles in varicella-zoster virus glycoprotein trafficking and virion envelopment

Varicella-zoster virus (VZV) encodes several glycoproteins which are present on both mature viral envelopes and the surfaces of infected cell membranes. Mechanisms of VZV glycoprotein transport and virion envelopment were investigated by both continuous radiolabeling and pulse-chase analyses with tritiated fucose in VZV-infected cells. We studied in detail the large cytoplasmic vacuoles which were present in infected cells but absent from uninfected cells. The specific activity in each subcellular compartment was defined by quantitative electron microscope autoradiography, using a cross-fire probability matrix analysis to more accurately assess the individual compartment demarcated by the silver grains. By these techniques, we documented a progression of activity originating in the Golgi apparatus and traveling through the post-Golgi region into virus-induced cytoplasmic vacuoles and finally to areas of the cellular membrane associated with the egress of viral particles. Significant amounts of radiolabel were not observed in the nucleus, and only low levels of radiolabel were associated with the cellular membrane not involved with the egress of viral particles. In addition, immunolabeling of Lowicryl-embedded VZV-infected cells demonstrated the presence of VZV glycoproteins within cytoplasmic vacuole membranes as well as on virion envelopes. These observations suggested that cytoplasmic vacuoles harbored VZV-specified glycoproteins and were also the predominant site of VZV virion envelopment within the infected cell. Neither enveloped nor unenveloped viral particles were observed within the Golgi apparatus itself.

Localization of fucosyl moieties in the mouse renal cortex by lectin histochemistry using the fucose binding lectins LTA and UEA I and by autoradiography using 3H-labelled fucose

The binding patterns of the two fucose binding lectins, Lotus tetragonolobus (LTA) and Ulex europeus I (UEA I) were investigated using fluorescence lectin histochemistry on the unfixed renal cortex of the mouse (NMRI) embedded in LR-Gold. The fluorescence staining results were compared with the autoradiographic localization of the incorporation of radioactive fucose into the renal cortex. For this study the turnover of incorporated 3H-fucose in the renal cortex was investigated 30 min, 2 h and 8 h after application. The localization of the radioactive fucose within the renal cortex corresponded well to the labelling pattern observed for lecting histochemistry using LTA. In contrast, with UEA I, no binding sites for this lectin could be observed. The results of our investigation clearly showed that fucosyl moieties in the renal cortex of the NMRI mouse are recognized by the fucose binding lecting LTA, but not by UEA I and that postembedding fluorescence histochemistry with LTA on the LR-Gold embedded kidney is a suitable technique for the localization of fucosyl moieties at the light microscopical level.

Immunocytochemical localization of alkaline phosphatase in absorptive cells of rat small intestine after colchicine treatment

The purpose of this study was to investigate the effect of colchicine and vinblastine on the localization of alkaline phosphatase (AlPase) in rat duodenum in relation to structural changes. AlPase was localized on the membranes of rough endoplasmic reticulum. Golgi stacks, cytoplasmic vesicles, microvilli, on lateral plasma membranes, and in some lysosomes of the duodenal epithelial cells of rats treated with either lumicolchicine or 0.9% NaCl alone. Microvilli were most intensely stained, and AlPase-positive Golgi stacks were regularly distributed in the supranuclear regions. After colchicine treatment, microvilli were shortened and the staining intensity became weaker, whereas basal as well as lateral plasma membranes showed stronger staining. The AlPase-positive microvilli appeared not only on the luminal surfaces, but also on the baso-lateral plasma membranes and even on the surfaces of characteristic intracytoplasmic cysts. Golgi stacks became smaller and their distribution became less localized, and the staining intensity of the Golgi stacks became weaker. AlPase localization in rats treated with vinblastine was almost identical with that of rats treated with colchicine. Thus, colchicine and vinblastine appeared to have elicited a disorientation of intracellular transport of intestinal AlPase by inhibiting microtubule organization.

Secretion of proteins and glycoproteins by perifused rabbit corpus epididymal tubules: effect of castration

Protein synthesis in epididymal tissue of intact and castrated rabbits was studied after incubation of epididymal minces with [35S]-cysteine or [35S]-methionine and protein separation by two-dimensional gel electrophoresis. Regional differences in the pattern of protein synthesized were observed. Castration did not change overall protein synthesis, but it reduced these regional differences. The presence of 5 alpha-DHT in the culture medium of the proximal corpus epididymidis perfused for 24 hr did not increase overall protein synthesis in tubules from intact or castrated rabbits and did not reinitiate synthesis of the proteins that had disappeared after castration. The kinetics of glycoprotein synthesis and secretion were studied by light and electron microscopy autoradiography at 0.5, 2, 6, and 24 hr after exposure to [3H]-mannose, [3H]-fucose, and [3H]-glucosamine. Changes in the distribution of mannose- and glucosamine-labeled material indicated that the decline in grain density over the epithelium from 30 min to 24 hr coincided with an increasing reaction over the stereocilia border from 30 min to 2 hr and in the lumen from 2 to 24 hr. The distribution of fucose-labeled material indicated that the grain reaction over the epithelium declined more rapidly than with the mannose label. When the glucosamine-labeled sperm mass was released from the tubules, the labeled material was lost after the first washing, indicating that the glucosamine-labeled glycoproteins did not bind firmly to corpus spermatozoa within 24 hr. After castration, both mannose- and fucose-labeled materials migrated to the cell apex more rapidly than in the intact animal, but they were not released as readily into the lumen. The culture of epididymal tubules from castrated males with 5 alpha-DHT for 24 hr did not promote the release of either mannose- or fucose-labeled material into the lumen. However, testosterone given in vivo for 2 weeks restored secretion of mannose-labeled material into the lumen.

Loss of microtubules and alteration of glycoprotein migration in organ cultures of mouse intestine exposed to nocodazole or colchicine

Explants from mouse jejunum were cultured for 3-7 h in the absence (control) or presence of colchicine (100 micrograms/ml) or nocodazole (10 micrograms/ml). In recovery experiments, explants were cultured in fresh medium for an additional period. To label glycoproteins, 3H-fucose was added during the last 3 or 6 h of the initial culture or recovery period. Subcellular fractionation studies revealed that colchicine and nocodazole inhibited migration of labelled glycoproteins to the brush border (P2) by 40-45%. Radioautographic studies of absorptive cells showed that colchicine and nocodazole inhibited labelling of the microvillous border by 67% and 87%, while labelling of the basolateral plasma membrane increased by 114% and 275%. Immunocytochemical studies revealed that both colchicine and nocodazole caused the virtual disappearance of the microtubular network in the absorptive cells. It is possible that some glycoproteins normally destined for the microvillous border are rerouted to the basolateral membrane. The observed loss of microtubules after drug treatment suggests that microtubules may play a role in the intracellular migration of membrane glycoproteins. Additional support for this concept is provided by the fact that in recovery experiments the distribution of label returned to control values after the microtubular network became re-established.