During microtubule depolymerization, the central, juxtanuclear Golgi apparatus scatters to multiple peripheral sites. We have tested here whether such scattering is due to a fragmentation process and subsequent outward tracking of Golgi units or if peripheral Golgi elements reform through a novel recycling pathway. To mark the Golgi in HeLa cells, we stably expressed the Golgi stack enzyme N-acetylgalactosaminyltransferase-2 (GalNAc-T2) fused to the green fluorescent protein (GFP) or to an 11–amino acid epitope, VSV-G (VSV), and the trans/TGN enzyme β1,4-galactosyltransferase (GalT) fused to GFP. After nocodazole addition, time-lapse microscopy of GalNAc-T2–GFP and GalT–GFP revealed that scattered Golgi elements appeared abruptly and that no Golgi fragments tracked outward from the compact, juxtanuclear Golgi complex. Once formed, the scattered structures were relatively stable in fluorescence intensity for tens of minutes. During the entire process of dispersal, immunogold labeling for GalNAc-T2–VSV and GalT showed that these were continuously concentrated over stacked Golgi cisternae and tubulovesicular Golgi structures similar to untreated cells, suggesting that polarized Golgi stacks reform rapidly at scattered sites. In fluorescence recovery after photobleaching over a narrow (FRAP) or wide area (FRAP-W) experiments, peripheral Golgi stacks continuously exchanged resident proteins with each other through what appeared to be an ER intermediate. That Golgi enzymes cycle through the ER was confirmed by microinjecting the dominant-negative mutant of Sar1 (Sar1pdn) blocking ER export. Sar1pdn was either microinjected into untreated or nocodazole-treated cells in the presence of protein synthesis inhibitors. In both cases, this caused a gradual accumulation of GalNAc-T2–VSV in the ER. Few to no peripheral Golgi elements were seen in the nocodazole-treated cells microinjected with Sar1pdn. In conclusion, we have shown that Golgi-resident glycosylation enzymes recycle through the ER and that this novel pathway is the likely explanation for the nocodazole-induced Golgi scattering observed in interphase cells.

We report here the characterization of gp27 (hp24␥ 3 ), a glycoprotein of the p24 family of small and abundant transmembrane proteins of the secretory pathway. Immunoelectron and confocal scanning microscopy show that at steady state, gp27 localizes to the cis side of the Golgi apparatus. In addition, some gp27 was detected in COPI-and COPII-coated structures throughout the cytoplasm. This indicated cycling that was confirmed in three ways. First, 15°C temperature treatment resulted in accumulation of gp27 in pre-Golgi structures colocalizing with anterograde cargo. Second, treatment with brefeldin A caused gp27 to relocate into peripheral structures positive for both KDEL receptor and COPII. Third, microinjection of a dominant negative mutant of Sar1p trapped gp27 in the endoplasmic reticulum (ER) by blocking ER export. Together, this shows that gp27 cycles extensively in the early secretory pathway. Immunoprecipitation and coexpression studies further revealed that a significant fraction of gp27 existed in a hetero-oligomeric complex. Three members of the p24 family, GMP25 (hp24␣ 2 ), p24 (hp24␤ 1 ), and p23 (hp24␦ 1 ), coprecipitated in what appeared to be stochiometric amounts. This heterocomplex was specific. Immunoprecipitation of p26 (hp24␥ 4 ) failed to coprecipitate GMP25, p24, or p23. Also, very little p26 was found coprecipitating with gp27. A functional requirement for complex formation was suggested at the level of ER export. Transiently expressed gp27 failed to leave the ER unless other p24 family proteins were coexpressed. Comparison of attached oligosaccharides showed that gp27 and GMP25 recycled differentially. Only a very minor portion of GMP25 displayed complex oligosaccharides. In contrast, all of gp27 showed modifications by medial and trans enzymes at steady state. We conclude from these data that a portion of gp27 exists as hetero-oligomeric complexes with GMP25, p24, and p23 and that these complexes are in dynamic equilibrium with individual p24 proteins to allow for differential recycling and distributions.

Abstract. A newly identified gene MK is transiently expressed in early stages of retinoic acid-induced differentiation of embryonal carcinoma cells (Kadomatsu, K., M. Tomomura, and T. Muramatsu, 1988. Biochem. Biophys. Res. Commun. 151:1312-1318. MK gene has been predicted to code a polypeptide that is rich in basic amino acids and cysteine and is not related to any other peptides so far reported. In the present study, we investigated MK expression during mouse embryogenesis by in situ hybridization. The MK transcript was detected all over the embryo proper of the 7-d embryo, while it was not detectable in the 5-d embryo. The ubiquitous expression continued in the 9-d embryo proper. On the 1 lth-13th d of gestation, the sites where MK gene was intensely expressed became progressively restricted; these sites were the brain ectoderm around the lens and brain ventricles, the anterior lobe of the pituitary gland, the upper and lower jaw, the caudal sclerotomic half of vertebral column, the limbs, the stomach, and the epithelial tissues of the lung, the pancreas, the small intestine, and the metanephros. These areas include the region where secondary embryonic induction is prominent. In the 15-d embryo, only the kidney expressed MK significantly. These data suggest that MK gene plays a fundamental role in the differentiation of a wide variety of cells; MK gene may also play some specific roles in generation of epithelial tissues, and remodeling of mesoderm.

SUMMARYWe used a specific monoclonal antibody to human hepatocyte growth factor activator inhibitor type 1 (HAI-1) in immunohistochemical procedures to determine the distribution and localization of HAI-1 in human tissues. In normal adult tissues, HAI-1 was predominantly expressed in the simple columnar epithelium of the ducts, tubules, and mucosal surface of various organs. In all cases, HAI-1 was localized predominantly on the cellular lateral (or basolateral) surface. By contrast, hepatocytes, acinar cells, endocrine cells, stromal mesenchymal cells, and inflammatory cells were hardly stainable with the antibody, and stratified squamous epithelium showed only faint immunoreactivity on the surface of cells of the basal layer. In the gastrointestinal tract, the surface epithelium was strongly stained. RNA blot analysis confirmed the presence of specific mRNA transcript in the gastrointestinal mucosa, and in situ hybridization revealed that HAI-1 mRNA showed a similar cellular distribution pattern. Although HAI-1 was not expressed in normal hepatocytes, strong immunoreactivity was observed on the epithelium of pseudo-bile ducts and on the surface of scattered hepatocytes in fulminant hepatitis. The enhanced expression was also noted in regenerating tubule epithelial cells of the kidney after infarction. We conclude that HAI-1 is preferentially expressed in the simple columnar epithelium of the mucosal surface and duct, that the predominant localization of HAI-1 is the cell surface, and that the expression of HAI-1 can be modulated by tissue injury and regeneration.

Ghrelin, a novel GH-releasing acylated peptide, was recently isolated from rat stomach. It stimulated the release of GH from the anterior pituitary through the GH secretagogue receptor (GHS-R). Ghrelin messenger RNA and the peptide are present in rat stomach, but its cellular source has yet to be determined. Using two different antibodies against the N- and C-terminal regions of rat ghrelin, we identified ghrelin-producing cells in the gastrointestinal tracts of rats and humans by light and electron microscopic immunohistochemistry and in situ hybridization combined with immunohistochemistry. Ghrelin-immunoreactive cells, which are not enterochromaffin-like cells, D cells, or enterochromaffin cells, accounted for about 20% of the endocrine cell population in rat and human oxyntic glands. Rat ghrelin was present in round, compact, electron-dense granules compatible with those of X/A-like cells whose hormonal product and physiological functions have not previously been clarified. The localization, population, and ultrastructural features of ghrelin-producing cells (Gr cells) indicate that they are X/A-like cells. Ghrelin also was found in enteric endocrine cells of rats and humans. Using two RIAs for the N- and C-terminal regions of ghrelin, we determined its content in the rat gastrointestinal tract. Rat ghrelin was present from the stomach to the colon, with the highest content being in the gastric fundus. Messenger RNAs of ghrelin and GHS-R also were found in these organs. Ghrelin probably functions not only in the control of GH secretion, but also in the regulation of diverse processes of the digestive system. Our findings provide clues to additional, as yet undefined, physiological functions of this novel gastrointestinal hormone.

ADP-ribosylation factor (ARF)-related protein 1 (ARFRP1) is a small GTPase with significant similarity to the ARF family. However, little is known about the function of ARFRP1 in mammalian cells, although knockout mice of its gene are embryonic lethal. In the present study, we demonstrate that ARFRP1 is associated mainly with the trans-Golgi compartment and the trans-Golgi network (TGN) and is an essential regulatory factor for targeting of Arl1 and GRIP domain-containing proteins, golgin-97 and golgin-245, onto Golgi membranes. Furthermore, we show that, in concert with Arl1 and GRIP proteins, ARFRP1 is implicated in the Golgi-to-plasma membrane transport of the vesicular stomatitis virus G protein as well as in the retrograde transport of TGN38 and Shiga toxin from endosomes to the TGN.Supplementary material available online at

Combinations of recently developed paradoxical concanavalin-A staining (PCS) and other routine histochemical procedures have made it possible to classify mucosubstances more precisely. By taking advantage of these sequences, the present study was undertaken both to characterize the mucinous contents of alimentary tracts of several animal species, and to compare the variability of epithelial mucosubstances with special reference to the mucous neck cells of the stomach. The alimentary tracts obtained from 7 species of fish, 5 amphibians, 3 reptiles, 4 birds, and 6 mammals were used. Acidity of epithelial mucosubstances was highly variable even among the corresponding mucous cells. On the contrary, concanavalin-A reactivity seemed to be consistent with each cell and species. The mucous neck cells, which were observed in amphibians, reptiles, and mammals, consistently exhibited a characteristic mucosubstance with stable class-III reactivity by PCS. Inversely, stable class-III reactivity was found only in species possessing mucous neck cells, and was widely distributed in the esophageal glands of the frog, snake, and man; in esophageal mucous cells of the frog and skink; in pyloric glands of amphibia, reptiles, and mammals; and in Brunner's glands of mammals. These mucous cells seem to form an unique group with morphological and histochemical similarities. It is likely that the stable class-III reactivity by PCS is a hallmark of the mucous neck cells and related glands and that, in addition, concanavalin-A reactivity of mucosubstances is evolutionarily more fundamental characteristic.

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