摘要:

Whole‐mount cell preparations of cultured rat 3Y1 cells were examined by stereo electron microscopy to identify the ultrastructural localization of concanavalin A (Con A) receptors in the plasma membrane, and to clarify the relationship between Con A receptors and cytoskeletal components. Well spread monolayer cells were extracted with saponin, briefly fixed, and then partially broken open with shearing force to facilitate the introduction of antibodies for identification of actin filaments. Stereo electron microscopy of such treated cells revealed a 3‐dimensional image of filamentous structures such as fine filaments, microtubules (MT) and endoplasmic reticulum (ER) in the flattened areas of each cell. Just beneath the plasma membrane were meshworks of actin‐containing fine filaments, as identified by an immunogold staining method. Microtubules and ER were observed to be either directly or indirectly associated with this meshwork. The broken open part of each cell exhibited a meshwork of filaments which were associated with the cytoplasmic surface of the plasma membrane. Some of the filaments were connected to the plasma membrane either by their ends or by their lateral surfaces. The localization of Con A receptors was examined by binding colloidal gold‐labelled Con A to the surface of fixed, saponin‐extracted cells. Virtually all gold particles bound externally at the same membrane sites where intracellular actin filaments attached internally. The observations strongly suggest that the distribution of Con A receptors was regulated by the underlying meshwork of actin

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00700.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Toxoplasma gondiimembrane fluidity was investigated by fluorescence polarization. We used 1,6‐diphenyl 1,3,5‐hexatriene (DPH) as a fluorescent hydrophobic probe. Fluorescence anisotropy (r) and degree of order (s) showed high fluidity properties. Chemical analysis was performed on this parasite. We found a low cholesterol/phospholipid ratio, many unsaturated fatty acid chains, and high phosphatidylcholine and low sphingomyelin amounts. These results were in good agreement with the observed high fluidity. This may be related to the great adaptability ofToxoplasma gondiiin infesting a wide variety of host ce

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00701.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The epidermis ofParalvinella grasslei(Polyhaete, Annelida) is covered by an extracellular matrix, the cuticle, mainly composed as in other annelids of superimposed layers of non‐striated collagen fibrils. The collagen fibrils of annelid cuticle are shown to be composed of parallel and sinuous microfibrils (thin section and freeze‐fracture replicas). The 3‐dimensional organization of collagen is characterized by 2 different types of geometrical order: (a) Fibrils form a quasi‐orthogonal network, whose structure is comparable to that of a “plywood”; (b) Fibrils are helical, and goniometric studies show that microfibrils present a definite order within each fibril, which is termed “cylindrical twist”. These 2 characteristics are those which have recently been evidenced in “blue phases”,i.e., liquid crystals which are closely related to cholesteic liquid crystalline phases. Non‐fluid analogues of cholesteric liquids are widespread among invertebrate cuticles and the presence of blue phase analogues suggests that a self‐assembly mechanism is involved in cuticle morphogenesis, which is derived from that governing blue phase growth. The cuticular network presents local rearrangements of fibrils called “defects”, despite the fact that they are elaborate structures which trigonal and pentagonal singularities. Branched fibrils are regularly observed. We discuss the involvement of these pattern disruptions in

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00702.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

In the present study, overall metabolism has been estimated in hybridoma cells by microcalorimetric measurement. Heat production rate was found to be 30–50 pW/cell at cell concentrations 0.65t‐4.5×105/ml. High cell concentrations (1×106cells/ml) caused unstable power‐curves with an initial high peak and a rapid declining phase, whereas low cell concentrations (0.6−4.5×105cells/ml) produced steady‐state power‐curves. Oxygen consumption was found to range between 1.5−6.1×10−5mol 02/cell/min, corresponding to about 80% of the total metabolic activity.The metabolic inhibitors sodium fluoride (50 mM), sodium azide (160 mM) androtenone (0.1 mM) caused a reduction in overall cell metabolism of 60, 55 a

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00703.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A new variant of multisystemic lipid storage myopathy (type 3) has been identified. Human cultured fibroblasts present a major triacylglycerol storage whereas other neutral lipids and phospholipids are in the normal range. When feeding the cells in the presence of radiolabelled oleic acid we observed an accumulation of radiolabelled triacylglycerols demonstrating the endogenous biosynthesis of the stored triacylglycerols. After a 72‐hr chase period, no degradation of radiolabelled triacylglycerols was observed. Histochemical examination of multisystemic lipid storage myopathy skin fibroblasts showed a massive accumulation of neutral lipids (stained by the fluorescent probe Nile Red) in cells grown in medium supplemented with 10% fetal calf serum. These cytoplasmic vacuoles were not obviously membrane‐surrounded as shown by electron microsc

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00704.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00705.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

We used a molecular approach to search for maternally expressed genes inDrosophila melanogaster. The relative merits of differential and competition screens were analyzed in a series of reconstruction experiments using either purified phage plaques or derivative DNA sequences. In the course of this study, we isolated 5 clones whose RNA level varies during early embryogenesis. Three gastrula differential clones, b4, b8 and d3, are present in numerous copies in the genome; clone b4 hybridizes with the copia‐like B104 repetitive sequence described by Scherret al.[29]. We also isolated 2 maternally‐expressed genes, not previously identified in either classical genetic or similarly molecular‐based screens. These clones, b11 and d6, map at cytogenetic positions 98F and 4F respectively, on the polytene chromosom

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00706.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Nucleoli and nucleolus‐associated chromatin (NAC) of radicle cells have been three‐dimensionally reconstructed from serial ultrathin sections during early germination ofZea mays. As a preliminary, the effect of 5 methods of fixation on the ultrastructure of the active NAC were tested qualitatively and quantitatively. It appeared that paraformaldehyde best preserved the fibrillar centres (FCs) and was consequently used for the 3‐D reconstructions. In quiescent cells, the NAC forms either 2 short internal strands about 0.7 μm thick running within the nucleolus or 2 peripheral knobs of the same diameter. Whatever its morphology, the NAC was composed of one clear zone,i.e., secondary constriction (SC) of the nucleolar organizer region (NOR), and one electron‐opaque zone,i.e., heterochromatic segment (HS). During germination the NAC was always connected to the nuclear envelope (NE) by a bridge of dense chromatin. The NAC strands or knobs of the quiescent cells are likely to be the counterpart of the 2 NORs of this species. 10–12 hr after onset of germination, one or several networks of nucleolar vacuoles were formed within which the whole NAC was located. Chromatin fibers about 12 nm thick emerged from unfolding portions of the NAC within these “nucleolar chromatin dispersal vacuoles” (NCDV). At 24 hr, the NAC appeared as 2 dichotomous strands. Seventy‐two hr after germination both the stretching out and branching of the NAC were more pronounced. After 120 hr, the transcribing ribosomal genes for each NAC strand together with the newly synthesized RNP transcripts formed a layer of dense fibrillar component surrounding a thin axis which was composed mainly of pale material. Together these formed a typical pl

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00707.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The principal structural compartments of the macronucleus ofEuplotes eurystomuswere examined by ultrastructural and cytochemical procedures. Interphase chromatin is condensed in highly compact granules that stain intensely with the DNA‐specific osmium‐amine procedure. Nucleoli react strongly with silver and with thiol‐specific reagents, but are almost completely unstained by osmium‐amine. The organelle of DNA synthesis, the replication band, is composed of 2 zones. The forward zone consists of highly ordered chromatin fibers, stains strongly with osmium‐amine, with silver, and with thiol‐specific reagents. The rear zone, which is the site of DNA synthesis, is impoverished in DNA, and is very sensitive to collapse induced byin vivoheat shock, or during nuclea

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00708.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Upon incubation with fluoresceinylated neoglycoproteins, isolated macronuclei from the ciliated protozoanEuplotes eurystomusdisplay different labelling patterns depending on the nature of the sugar bound to the neoglycoproteins. Specific sugar‐binding components (i.e., lectin‐like molecules) are associated with presumed nucleoli and with the macronuclear replication bands. This is the first demonstration that DNA synthesis and sugar‐binding components are co‐localized in an eukaryot

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1988.tb00709.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY