摘要:

Summary—The eucaryote cell cycle is driven by a set of cyclin dependent kinases (CDKs) associated to cyclins, which confer not only the activity but also the substrate specificity and the proper localization of the kinase activity. In the fission yeastSchizosaccharomyces pombe, only one cyclin, the product of thecdc13gene (p56cdc13), is required to be associated with p34cdc2, to control the complete cell cycle. Earlier studies have localized this complex mainly in the nucleus and its periphery. Using new improved electron microscopy (EM) technologies, based on high pressure freezing fixation, we refined previous studies, evidencing cytoplasmic localization of p56cdc13, in addition to the nuclear localization previously observed. Further immunofluorescence studies, performed on aldehydically fixed cells, confirmed our EM results, emphasizing the major cytoplasmic localization of p56cdc13in interphase cells and the relocalization towards the nucleus in mitotic cells, suggesting that theS pombecyclin B localization is cell cycle‐regula

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00949.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—Giardia lamblia, a major cause of intestinal disease worldwide, is a parasitic protozoan that represents the earliest branch of the eukaryotic lineage. Trophozoites, which possess two nuclei but lack mitochondria, peroxisomes and a typical Golgi apparatus, colonize the small intestine of the vertebrate host where they may differentiate into infective cysts. Encystation is a regulated process characterized by the biosynthesis, secretion and formation of a protective extracellular cyst wall. In previous studies, we demonstrated the biogenesis of the Golgi apparatus during encystation and identified two leucine‐rich proteins (CWPs), which localize within encystation‐specific secretory granules before their incorporation into the cyst wall. Here, we used immunological, biochemical and molecular biological approaches to analyze the expression of BiP/GRP78, an endoplasmic reticulum (ER)‐resident chaperone, during theGiardialife cycle. A monoclonal antibody specific forGiardiaBiP permitted the visualization of the ER of this protozoan and showed that BiP expression increased simultaneously with the increased expression of CWPs during encystation. However, in contrast to the 140‐fold increase in levels of CWP transcripts, the steady‐state level of BiP mRNA did not increase during encystation. Furthermore, potent inducers of BiP expression in higher eukaryotic cells, including agents that perturb the ER environment, did not affect BiP expression inGiardia. These results, when considered together with the profound changes that occur in the secretory pathway duringGiardiaencystation, indicate an important role for this molecular chaperone during the differentiation of this primitiv

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00950.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—Recently, several proteins immunologically related to erythrocyte membrane skeletal proteins, such as protein 4.1 and fodrin (non‐erythroid spectrin), have been found in keratinocytes. In the present study, in order to investigate the roles of these proteins in cell‐cell contact, we analyzed the distribution of non‐erythroid protein 4.1, β‐fodrin and actin in cultured human keratinocytes at low (0.15 mM) and standard (1.85 mM) Ca2+concentrations. Immunofluorescence microscopy revealed that immunoreactive forms of protein 4.1, β‐fodrin and actin filaments were present in the cytoplasm of cells cultured in low Ca2+medium, while in cells in the standard Ca2+medium, these proteins were localized at the cell boundary and partially in the cytoplasm. When cells in the low‐Ca2+medium were treated with 100 nM 12‐O‐tetradecanoylphorbol‐13‐acetate (TPA) for 1 h, these proteins were also present at the cell boundary. Increasing extracellular Ca2+concentration from low to standard in the medium induces cell‐cell contact among the cultured human keratinocytes, accompanied by the translocation of protein 4.1 and β‐fodrin from the cytoplasm to the membrane. On the basis of the present study, movement of membrane skeletal proteins from the cytosol to the membrane suggests that either these proteins or the membrane skeletal lattice plays an important role in the regulation of cell‐cell intergigitations in response to changes in the Ca2+concentrations in culture medium, and that phosphorylation of these skeletal proteins might be involved in the regulation of the membrane skeletal proteins of ker

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00951.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—The distribution of smooth muscle (SM)‐type myosin heavy chain isoforms in several bovine muscular and non‐muscular (NM) tissues was evaluated by immunofluorescence tests using monoclonal antibodies SM‐E7, reactive with 204 (SM1) and 200 (SM2) kDa isoforms, and SM‐F11, specific for SM2 isoform. SM‐E7 reacted equally with vascular, respiratory and intestinal SM tissues, whereas SM‐F11 stained heterogeneously SM cells in the various muscular systems examined and in some peculiar tissues was unreactive (perisinusoidal cells of hepatic lobule, pulmonary interstitial cells and intestinal muscularis mucosae) or uniquely reactive (nerve cells). On the whole, our findings indicate that SM1 and SM2 isoforms are unequally distributed at the cellular level in various SM and NM tissues and support previous results obtained with tissue extracts and electrophoret

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00952.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—Regulated exocytosis of defensive secretory organelles, the trichocysts, as well as a transient Ca2+‐influx can be induced inParameciumby aminoethyldextran (Kerbœuf and Cohen,J Cell Biol(1990) 111, 2527). Knollet al (Febs Lett(1992) 304, 265) reported that veratridine was also a secretagogue forParamecium. Here we show that, like aminoethyldextran, veratridine induces a transient Ca2+‐influx. Both aminoethyldextran‐and veratridine‐induced exocytosis and associated Ca2+‐influx were: i) blocked in thend12thermosensitive mutant at the non‐permissive temperature; and ii) inhibited by amiloride and four divalent cations, Ba2+, Mg2+, Sr2+and Co2+. This suggests that, although of different chemical nature, aminoethyldextran and veratridine act through the same physiological pathway. In addition, the inhibitory doses are comparable to the ones found to inhibit a hyperpolarization‐sensitive Ca2+‐current described inParamecium(Prestonet al(1992)J Gen Physiol100, 233). The possibility that the activation of this Ca2+‐current by the secretagogue represents an early step in the regulation of trichocyst exo

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00953.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—The blood‐brain barrier (BBB) preventing the passage of proteins is established at day 13 of development in the embryonic chick brain. We describe, as early as this stage, the existence of characteristic tight junctions between endothelial cells that is related to the time of appearance of the basal lamina. At earlier stages (E10, E12), when endothelial cells seem to be held back from the glio‐neural neuropile by fibroblast‐like cells identified by their appearance and position, the astrocyte plasma membranes already present a rare but characteristic molecular arrangement: the orthogonal arrays of particles (OAs). These OAs become progressively more abundant in astrocytic plasmalemmas contiguous to endothelial cells when these cells have been surrounded by the basal lamina since E15. The contact between astrocytes and basal lamina therefore seems to favor a high density of OAs, as has been shown in vertebrate astrocytes in contact with endothelial cells or leptomeninges. No correlation exists between the onset of the BBB and the time of appearance

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00954.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—The replica staining label fracture technique was used to analyse the distribution of cruzipain and Ssp4 inTrypanosoma cruzi. Intense labeling for the two proteins was seen on the E fracture face of amastigote forms. Gold particles did not co‐localize with the intramembranous particles. Labeling was abolished by previous treatment of the parasites with phospholipase C fromTrypanosoma brucei, which removes glycosylphosphatidyl inositol (GPI) anchored proteins. These observations suggest that cruzipain and Ssp4 are attached to the parasite surfaceviaa GPI anc

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00955.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—Ultrastructural and microanalytical investigations of the pericardial gland of the freshwater mussel,Dreissena polymorphahave been performed to investigate the possible functional role of this organ in the detoxication process of lead. The cell‐type of this organ exhibits the feature characteristics of podocytes,iethe typical pedicel‐basal lamina complex and the well developed lysosomalvacuolar system. X‐ray microanalysis demonstrated that large electron‐dense granules referred to as lysosomes are the main target organelles in these cells to accumulate and sequestrate lead where the metal was associated with phosphorus and sulphur. Consequently, the pericardial gland plays an important role in the detoxication process and allows the organism to tolerate high lead concentration without suffering severe ce

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00956.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—A useful experimental system from primary cultures of hemocytes fromHaliotis tuberculatahas been established. Six days after initiation of the culture, the viability of hemocytes remained constant as measured by the MTT assay. In addition, hemocytes showed physiological responses as judged by protein and DNA syntheses in response to treatment with vertebrate growth factors. Porcine insulin and human epidermal growth factor (EGF) stimulated [3H]‐leucine and [3H]‐thymidine incorporation in hemocytes in a dose‐dependent manner. No additive effect of insulin and EGF is observed either for [3H]‐leucine or for [3H]‐thymidine incorporation. The response of primary cultures of abalone hemocytes to vertebrate growth factors confirms their growth potentialin vitroand provides a suitable model for further studies on regulation of the control of cellular processes such as cell growth, differentiation and migration in inverte

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00957.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

Summary—Normal and otosclerotic bone cells were culturedin vitroin serum‐free medium to evaluate single glycosaminoglycan (GAG) class synthesis and secretion. Moreover, the degradative process was studied by inhibiting the lysosomal functions through the addition of ammonium chloride to the cultures, an ammine known to inhibit lysosomal degradation by neutralizing organelle activity. Otosclerotic bone cells accumulated a lower amount of GAG both in the cellular and extracellular pool compared to normal ones. The decrease was markedly higher for secreted GAG. Moreover a different pattern of single GAG class distribution was observed in the two cell types considered. In the medium of otosclerotic cells a percentage increase of hyaluronic acid (HA) and dermatan sulphate (DS) and a percentage decrease of heparan sulfate (HS) and chondroitin sulfate (CS) were observed compared to normal bone cells. Ammonium chloride had a lower effect on pathologic than on normal cells, indicating a decrease in the degradative process in otosclerotic bone cells. These results were also confirmed by the experiments on GAG uptake and degradation and by the dosage of enzymatic activity of two exoglycosidases. Since extracellular GAG composition influences bone deposition and mineralization, these data support the hypothesis that otosclerosis is the result of an error in the connective tissue matrix struct

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1996.tb00958.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY