摘要:

Summary—Fibroblast growth factors (FGFs), first extracted from brain and retina, are potent neurotrophic factors. They stimulate neuroblast proliferation and neuron differentiation and survival. In order to study the spatial and temporal distribution of the target cells in the mouse brain we studied by autoradiography and quantified by image analysis125I‐bFGF binding sites as a function of development. We have revealed the presence of two types of specific bFGF receptors. One is heparitinase sensitive and is co‐localized with heparan sulfate proteoglycans of the basement membranes (meninges, choroid plexus and blood vessels). It is not developmentally regulated and corresponds to the low affinity receptors. It may be a storage form. The second type is heparitinase resistant and is modified during development, matching, in the adult, layering of the hippocampus and cerebellum. At 13 days of embryonic development there is a preferential distribution of silver grains on the ecto‐ and neuroectodermal tissues. In the adult, the labeling is localized on the neural process layers. It likely corresponds to the specific binding to cell high affinity receptors. Binding patterns according to the developmental stages of the brain can be correlated with mitotic, migration and differentiation phases of the neurona

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90189-8

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—In the current study the internucleosomal DNA cleavage activity associated with apoptosis was investigated in avian thymocytes. Thymocyte nuclear proteins from glucocorticoid‐treated chickens were incubated with chicken red blood cell (cRBC) nuclei, and DNA degradation was analyzed by agarose gel electrophoresis and fluorescence‐activated flow cytometry. The thymocyte nuclear extract contained an endonuclease activity that degraded cRBC chromatin at internucleosomal sites as detected by agarose gel electrophoresis. Flow cytometry analysis of cRBC nuclei that were treated with thymocyte nuclear proteins demonstrated a loss of cellular DNA as a function of the amount of added nuclease activity. Furthermore, it was demonstrated that the thymocyte nuclear extract contained a nuclease activity that was capable of degrading radiolabelled naked32P‐DNA into acid soluble DNA fragments. All three assay methods demonstrate that the thymocyte nuclease activity can be inhibited by EDTA, zinc ions and the nuclease inhibito aurintricarboxylic acid. Based on the analysis of cofactor requirement of this nuclease activity and its susceptibility to inhibitors, the endonuclease activity present in avian apoptotic thymocytes appears to be identical to the mammalian coun

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90190-C

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Cleavage furrows of amphibian eggs exhibit characteristic morphological features; the presence of finger‐like microvilli (MV) along their outer edges, the formation of furrow walls from new plasma membrane lacking MV, and the subsequent retrieval of this membrane during the infolding of the furrow. A similar structure can be induced, specifically, by certain cytoplasmic components such as centrosomes, polyamines and calcium. Their respective roles in the events associated with the furrowing process have been investigated by injecting these agents into nucleated and enucleatedPleurodeleseggs and evaluating their effects using cytochemical labelling of the egg surface with a biotin‐streptavidin system. The injection of polyamines (spermine or spermidine) and in some cases, calcium into enucleated eggs provoked MV elongation and the appearance of newly formed, smooth plasma membrane. In these eggs, this membrane was not incorporated into the furrows, and as a consequence, the blastomeres did not actually separate. In contrast, the injection of centrosomes into enucleated eggs induced both the incorporation and internalization of new membrane, resulting in the formation of furrows and a true cellularization of the eggs, identical to the cleavage process observed in fertilized eggs. The present results provide further evidence that the establishment of the furrow depends on two complementary interacting systems: the contractile elements of the egg cortex which regulate the insertion of new membrane and the mitotic center which is essential for the invagination of the f

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90191-3

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—Dinoflagellates possess two flagella. One of them, the longitudinal flagellum, retracts from time to time in some species, such asCeratiumandPeridinium. Additional structures which run along the axoneme seem to be responsible for this particular behaviour. The retraction which is rapid (less than 60 ms) may be subdivided into several steps: i) the undulating movement stops; ii) the flagellum appears then as a jagged line during 20 ms; iii) finally a rapid retraction (20 ms) takes place, the flagellum being folded 20 times inside the cylindrical flagellar pocket. The measurements on video‐records suggest that the R‐fibre shortens to 30% of its original length. The contraction and relaxation mechanism of nanofilaments is proposed to be through coiling and uncoiling dependent on Ca2+concentr

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90192-4

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The gene encoding mouse peripherin, a neuronal intermediate filament protein, has been cloned. Its sequence, through 1021 nucleotides composing the 5′‐flanking region, nine exons, eight introns and 547 nucleotides of the 3′‐flanking region, as well as its transcription initiation site have been determined. The amino acid coding sequence differs from that of the rat peripherin gene. The mouse gene has an additional histidine near the N‐terminal end, and shows three conservative and two non‐conservation changes. The promoter sequence, containing the binding sites for transcription factors as well as other sequences is homologous to promoter regions of other type III intermediate filament protein genes and other neuronal

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90193-5

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The accumulation of autofluorescent lipofuscin was quantified in cultured human retinal pigment epithelial (RPE) cells phagocytosing bovine rod outer segments (BROS) and the expression of proteins in these cells was investigated. Results showed a steady increase in autofluorescence of RPE cells over a 4‐week period as measured by fluorophotometric flow cytometry. A significantly greater increase in autofluorescence was found in the cultured RPE cells from a 7‐year‐old donor compared with those from a 47‐year‐old donor. Within both groups the BROs‐challenged cells had significantly higher fluorescence readings than the control cells which were not challenged. Autoradiography of35S‐labelled proteins separated by polyacrylamide gel electrophoresis (PAGE) revealed a small distinct band at 102 kDa in BROS‐challenged RPE cells of both bovine and human origin that did not appear in control or microsphere‐phagocytosing RPE cells. The intensity of the signal was unrelated to the duration of t

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90194-6

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—In this study we describe the production and characterization of two monoclonal antibodies (mAb 503 and mAb 703) raised against the apical membrane of rabbit cortical collecting tubule (CCT) cells. The specificity of the two monoclonal antibodies was studied by immunoelectron microscopy on kidney sections. These antibodies were used to identify principal and intercalated cells in primary cultures of CCT. To assess the maintenance of the basic characteristics of the cortical collecting cells during the growth process we determined the biochemical and electrophysiological properties of cultured CCT. Of the monoclonal antibodies produced mAb 503 was specifically directed against the luminal membrane of intercalated cells as shown by immunoelectron microscopy. mAb 703 bound specifically the apical membrane of the principal cells. In primary cultures of CCT mAb 503 and mAb 703 bound antigens present on the apical membrane of different cells and permitted the study of the distribution of the two cell types. Results showed the maintenance of the epithelial polarity of cultured CCT and the expression of specific antigen

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90195-7

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The interphase nucleus of the green alga,Chlamydomonas reinhardtii, displayed two types of bodies some of them, the dense bodies, lying apparently free in the nucleoplasm while the others were attached to the nucleolus and were, therefore, referred to as nucleolus‐associated bodies (NABs). The presence of DNA, RNA and histones in dense bodies was investigated by means of post‐embedding immunocytochemistry and cytochemistry using a monoclonal antibody to single and double stranded DNA, a polyclonal antibody to rye H3 histones and RNase A‐gold complexes. The dense bodies were shown to contain significant amounts of RNA but neither DNA nor histones were detected; their composition was thus similar to that of the dense bodies described in higher plant cells. We propose that dense bodies might be implicated in the assembly of the 25 to 45 nm granules observed throughout the nucleoplasm ofChalamydomonasinterphase nuclei. The composition of NABs was found to be distinct from that of the dense bodies since they were labeled by the antibody to DNA, specially in cryofixed and cryosubstituted specimens. The presence of DNA in NABs together with their intimate association to the nucleolus suggest that they may correspond to specific segments of chro

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90196-8

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The ultrastructural organization of the interphase nucleus of the green algaChlamydomonas reinhardtiiwas investigated and found to be largely dependent on the fixation conditions. In specimens stained with bismuth, densely contrasted granules ranging from 25 to 45 nm in diameter were localized throughout the interchromatin space and often formed clusters. These granules were labeled by RNase A‐gold complexes and may represent the counterparts of animal and higher plant cll interchromatin granules. Within the nucleolus the Ag‐NOR and pyroantimonate stains and, to a lesser extent, the bismuth stain reacted with the nucleolar dense fibrillar component (DFC). When cells were subjected to a heat shock at 42°C, the nucleolar DFC was found to progressively separate from the nucleolus and, after 3 h, appeared as a continuous meandering thread about 0.1 μm in width. Within the nucleolus, labeling on conventional preparations occurred as small clusters with antibodies to H3 histones or to DNA whereas RNase A‐gold complexes labeled most of it including fibrillar centers. Improved ultrastructural preservation in cryofixed, cryosubstituted specimens gently fixed in glutaraldehyde permitted to localize nucleolar DNA predominantly at the outer edge of fibrillar centers and to a lesser extent within the neighbouring DFC. Our results indicate that the structure and composition ofChlamydomonasinterphase nuclei are comparable, despite particularities, to those of animal and higher pla

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90197-9

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Summary—The cellulose‐protein fibrils, which constitute by far the bulk of the fibrous fraction of the sea peach tunic (Halocynthia papillosa), were structurally and chemically characterized, eitherin situor after extraction procedures, with the use of classical electron microscoy combined with diffraction contrast imaging and electron diffraction, histochemistry, affinity cytochemistry and chemical analysis. These fibrils exhibit a cross‐sectional shape close to a parallelogram. The cyrstallites forming their core, with lateral dimensions ranging from roughly 5 to 20 nm, are composed of native cellulose of higher crystallinity than that of plant cellulose. They are associated with acid mucopolysaccharidés (amps) and proteins which form a coating material appearing as a continuous sheath enveloping the axial crystallite in the cuticular layer or as patches more‐or‐less periodically distributed around and along the fibre axis in the fundamental layer. Tunicin, the alkali‐insoluble fibrous fraction, is not pure cellulose, yielding only 22–60% of its dry weight as glucose equivalents, depending on the tunical layer. It is suggested that in addition to the high degree of crystallinity of the tunical cellulose, the presence of a significant amount of coating material composed of amino acids and proteoglycans firmly linked to cellulose molecules contributes to tunicin's high resistance

ISSN:0248-4900    

DOI:10.1016/0248-4900(92)90198-A

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY