摘要:

Summary—Our results show that stimulation by serum of dense cultures of 3T3 cells rapidly induced increased synthesis of a growth inhibitor (mIGFBP‐3) capable of binding IGF. mIGFBP‐3 was secreted by stimulated cells immediately after its synthesis, and accumulated in the medium. Accumulation of mIGFBP‐3 in the medium increased, as a function of growth factor (bFGF, PDGF, insulin) concentrations and time. bFGF was the best stimulatory factor for both DNA synthesis and accumulation of mIGFBP‐3 in the first 24 h of incubation. DNA synthesis was arrested after 48 h of incubation with bFGF when accumulation of mIGFBP‐3 was maximal. Since we showed that mIGFBP‐3 is able to inhibit bFGF stimulation of DNA synthesis in mouse fibroblasts, it is possible that the accumulation of mIGFBP‐3 induces a feedback regulation

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90204-E

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The objective of this work was to characterize lipid metabolism in long‐term cultures of adult rat hepatocytes from female rats and explore the potential use of this culture system to study the effect of hormones, drugs and toxic chemicals on it. Hepatocytes, seeded on a feeder layer of 3T3 cells, maintained for 2 weeks their typical morphology. The cultures were able to take up [14C]acetic and [14C]oleic acid from the culture medium and incorporate them into lipids. The synthesis and secretion of lipids by [14C]acetic acid‐labeled cultures had a maximum value after 11 and 13 days in culture. Triacylglycerols were the main lipidic species synthesized and secreted by hepatocytes (up to 67% of the total lipids); they also synthesized and secreted phospholipids, cholesterol and cholesterol esters from [14C]acetic acid. Similarly, [14C]oleic acid‐labeled cultures synthesized and secreted mostly triacylglycerols (up to 60–70% of the total lipids), but they were also able to incorporate the labeled precursor into both cellular and secreted phospholipids and cholesterol esters. The activity of glycerol‐phosphate‐dehydrogenase, marker enzyme of glycerolipid synthesis, decreased slightly during the culture time whereas the activity of malic enzyme, marker of fatty acid synthesis, increased. Our results show that long‐term cultures of female rat hepatocytes are able to synthesize and secrete several lipids, specially triacylglycerols, from both [14C]acetic and [14C]oleic acid for at least 2 weeks and that they maintain enzyme activities related with the synthetic pathways of glycerolipids and fatty acids. They also suggest that these cultures could be a useful model system to study lipid metabolism and the effect of hormones, drugs and toxic

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90205-F

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Formation of progeny viruses in the nuclei of HeLa cells infected with adenovirus type 5 was studied at the ultrastructural level byin situhybridization techniques allowing specific detection of either viral double‐stranded DNA (dsDNA) or single‐stranded DNA (ssDNA). Prior to the initiation of replication of viral genomes, infective DNA molecules which entered the nucleus of the target cell were randomly distributed among host chromatin fibers including nucleolus‐associated chromatin. They were double‐stranded, that is, without single‐strand breaks. Such association of viral DNA with host condensed chromatin also occurred in mitosis. The initiation of viral genome replication occufred simultaneously with the appearance in the nucleoplasm of small fibrillar regions containing intermingled viral dsDNA and ssDNA. Later, at the intermediate stage of nuclear transformation, viral dsDNA and ssDNA molecules were almost entirely separated into two contiguous substructures. At this stage, viruses were observed occasionally in the vicinity of viral ssDNA accumulation sites. Still later, an additional substructure developed in the centre of the nucleus which consisted of large quantities of viral dsDNA, traces of viral ssDNA and abundant viruses. Portions of viral ssDNA were attached to some viruses even at late stage of nuclear transformation, an association which strongly suggests the occurence of encapsidation of at least some of the viral genomes while they are still engaged in

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90206-G

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—DorosphilaC virus (DCV) cycle duringDrosophila melanogasterdevelopment was studied after feeding contamination at the first, most sensitive, instar (L1). TwoDrosophilastrains were examined and compared. Presence of DCVCin apparently healthy animals (L3 larvae bred on a contaminated rearing medium and adults coming from larvae which were grown on medium containing DCVC) was demonstrated by biological tests. Using the immunofluorescence technique, DCV was exhibited in the diseased Charolles larvae, in the lumen of the digestive tract and in the basal part of gut cells which is in contact with the haemolymph. On the contrary, in Charolles larvae which seemed ‘healthy’, DCV was exhibited only in the lumen of the digestive tract at the apical boundary of the gut cells. But DCV typical protein capsid was not shown in the tissue ofDrosophilaL3 and adults. However, C virus remained inDrosophilatissues even after host metamorphosis and would seem to interact withDrosophilacells. Hypotheses are proposed concerning the intracellular state ofDrosophilaC virus in this

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90207-H

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The ribonucleoprotein components of the nucleus of chick embryo muscle cells in different stages of development were studied by electron microscopic quantitative stereology. The changes of the constituents were related with the appearance of the innervation by means of silver impregnation for light microscope. The numerical density of the perichromatin granules (PCG) is low in mononuclear cells and myotubes. It is noteworthy that the frequency of the PCG does not change during the transition of the cells in mitotic cycle to postmitotic myoblasts and during myofibril differentiation. However, there is an important increment in this parameter when the motor nerve fibers arrive at the muscle and the synaptic contacts are established. This change is correlated with appearance, or at least with a great increasé, of the importance of posttranscriptional controls of the expression of some genes. The augmentation in the frequency of PCG is not accompanied by alterations of the abundance of total RNP particles, in close resemblance with the phenomena occurring in neuroblast during the differentiation of synaptic endings. The variations of the nucleolar volume coincide with the changes in rRNA synthes

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90208-I

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—We investigated the presence of dystrophin by immunoblot and immunofluorescence analyses, negative staining, rotatory shadowing and immunogold electron microscopy in chicken cardiac muscle. Saponin was found to be better than Triton X‐100 for providing a new ‘dystrophin‐enriched’ solution for use in biochemical studies of the molecule. By Western blot analysis, only a 400‐kDa band was revealed with polyclonal antibodies directed against a central region (residues 1178–1723) of the dystrophin molecule and no cross‐reactions with other proteins or degraded products were observed. Specific cleavage of the dystrophin molecule showed that the central rod‐shaped domain corresponded to a resistant ‘core’. This structure might rigidify the protein. By immonofluorescence, dystrophin was localized at the periphery of cardiac ventricular cells. The molecule was examined by electron microscopy and found to have variable lengths (140–160 nm for the monomeric from and about 260 ± 10 nm or more for oligomeric forms). These oligomeric structures are considered to be associated molecules which are only partially overlapped lengthwise. The precise distribution of dystrophin within the cardiac muscle was determined by visualisation of gold particles in immuno‐electron microscopy. Gold particles were found on the sarcolemma with no evidence of any association with cytoplasmic structures. The present data provide further details on the cardiac dystrophin molecule and suggest that its capacity of self‐association may ela

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90209-J

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—S‐antigen (arrestin) is a cytosolic protein which regulates phototransduction in retinal rods. A protein immunologically related to S‐antigen was identified in fractions from soluble extract of bovine kidney enriched by gel filtration or by immunoaffinity chromatography using a polyclonal antibody to retinal S‐antigen. On immunoblots, this protein was recognized by a panel of monoclonal antibodies (mAbs S2D2, S1A3 and S9E2) directed against different S‐antigen epitopes and displayed the same apparent molecular mass (48 kDa) as retinal S‐antigen. All three mAbs revealed a specific immunoreactivity by indirect immunocytochemical technique on rat kidney sections. The three mAbs recognized some but not all glomerular cells, identified as epithelial cells by immunoelectron microscopy using the mAb S9E2. Both mAbs S2D2 and S1A3 gave a diffuse cytoplasmic staining in all tubule cells. Proximal tubule cells exhibited a weak immunoreactivity, whereas distal and collecting tubule cells were strongly labeled. In contrast, the mAb S9E2 immunoreaction was restricted to a cell subpopulation from distal and collecting tubules corresponding to intercalated cells identified by immunoelectron microscopy. With the mAb S9E2, the labeling of proximal tubule cells was localized in the apical region of the cytoplasm. These results suggest that two or more 48‐kDa proteins immunologically cross‐reactive with retinal S‐antigen are present in kidney. The observed pattern of distribution is in keeping with the hypothesis that such proteins could play a role in the regulation of G‐protein‐related receptors present in renal glomerules and tu

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90210-R

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Changes in characteristic components of the skin epidermis of the large tadpole ofPelobates syriacuswere studied throughout its development. The fate of two specific cells in the skin epidermis was followed, from the young tadpole to the adult was studied. It was found that flask‐shaped type cells in the tadpole epidermis which are PAS‐positive, stain with peanut lectin (PNA). There is not detectable band 3 in the premetamorphosed stages, and mitochondria‐rich cells are very rare. This pattern of staining changes completely upon metamorphosis: the PAS‐positive cells, specific to the tadpole epidermis disappear, and the mitochondria‐rich (MR) cells in the adult skin epithelium react with polyclonal anti‐band 3 antibody. Western blot analysis showed the presence of a band 3‐like protein of about 95 kDa, only in the adult epithelial extract, coroborrating the immunocytochemical observations. The finding of the presence of band 3‐like protein in the MR cells ofPelobates, is similar to the observations made in the skin of other amphibian species. On the other hand, the binding of peanut lectin to MR Cells is species‐specific, since it does not react with the MR cells in the skin epithelium o

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90211-I

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The morphogenesis of basal bodies is described in the phytoflagellatePolytoma papillatum. The observations are based on the analysis of ultrathin serial sections through the flagellar apparatus of interphase, mitotic, and postmitotic cells using transmission electron microscopy. Formation of new basal bodies starts in prometaphase. Individual A‐subfibres develop orthogonally to the long axis of mature basal bodies. The microtubules assemble at the surface of an annulus of amorphous material. By telophase, a complete cylinder of A‐subfibres with a length of approximately 300 nm has formed. Although the proximal ends of these new probasal bodies are detached from the mature basal bodies, prominent reorientation of the probasal bodies does not occur. They remain with their proximal ends in the vicinity of mature basal bodies. In daughter cells with probasal bodies around 400 nm long, the assembly of microtubular triplets is initiated. B‐ and C‐subfibres first show up distal from the mature basal bodies and may elongate towards them. Thus, A‐subfibres on the one side and B‐ and C‐subfibres on the other appear to growt with opposite polarity. If A‐subfibres grow at their plus ends, B‐ and C‐subfibres elongate at their minus ends. The latter is unusual in comparison with individual cytoplasmic and spindle microtubules. Possible the presence of a lateral template in the form of the A‐subfibres is responsible for the deviating growth characteristics of the incomplete B‐ and C‐subfibres. In interphase cells, the mature basal bodies extend into long flagella. The new basal bodies remain devoid of flagella and are less than 85 nm long. Thus, they have shortened relative to their precursors in mitotic and postmitotic cells. At the onset of a new division cycle, the flagellate basal badies shed their flagella. The breaking point is at the triplet‐double

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90212-J

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Deep‐sea hydrothermal vent worms livé in tubes made of giant β‐chitin crystallites (50 nm in diameter, several μm in length) embedded in a protein matrix. These chitin cyrstallites form a liquid‐crystal‐like structure differing from the wellknown cholesteric arrangement of classical chitin‐protein systems. Furthermore, and in contrast with the latter systems, the vestimentiferan chitin‐protein systems are produced by goatskin‐shaped glands. Rod‐shaped elements in the lumen of these glands were identified by DCTEM and Au‐WGA labeling and freeze fracture as chitin crystallites. The main characteristics of these “chitin secreti

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90213-K

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY