摘要:

The four small nucleoplasmic RNAs designated as U1, U2, U4 and U5 RNA have a common structural domain or domain A. It is characterized by the presence of consensus sequence Pu‐A‐(U)5‐G‐Pup in a free single‐stranded region and of the sequence Py‐N‐Py‐Gp in the top loop of a hairpin located at the 3′ end of the free region. Domain A is likely to be involved in a function common to the four small RNAs. Other domains possibly involved in the specific function of U1 and U5 RNAs are also presented. Several molecular forms of a same U RNA may be found in a same cellular type. These variant U RNAs are particularly numerous for U5 RNA. The possible origin of such new molecular forms is discussed in relation to multigene families for U RNAs. U1, U2, U4 and U5 RNAs are capped (with trimethylguanosine) and the consensus sequence for their 6 first nucleotides is A‐(Py)5p. Thus, their 5′ end resembles that of premessenger RNA, also capped (with monomethylguanosine) and bearing A‐(Py)5p. Both classes of RNA are synthesized by RNA polymerase B, but the presence of a “TATA box” upstream of the capsite has not yet been demonstrated for U RNA genes. U1, U2, U4 and U5 RNAs bear a sequence C‐Py‐Pu at their 3′ end or very close to it. This trinucleotide might be part of a site of post‐transcriptional cleavage of U RNA precurso

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00278.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Despite the fact that the fibrillar centers of the nucleolus and the chromosomal nucleolar organisers (NORs) are similarly stained with the NOR‐silver technique, there remain some questions about the identification of fibrillar centers as NORs. The distinct delineation of the fibrillar centers in porcine thyroid cells allowed us to determine whether there was a numerical equivalence or correlation between fibrillar centers and NORs. Hybridization in situ and silver staining performed on pig chromosomes showed that pairs 8 and 10 contained rDNA sites. Silver staining of thyroid cells in electron microscopy showed that the fibrillar centers and their surrounding layer of dense fibrils were the sites of silver deposit. Chromatin fibers were demonstrated within the fibrillar centers through the aid of the osmiumammine reaction and with the oxidized diaminobenzidine technique. It was observed that in cultured thyroid cells the fibrillar centers could be identified in the light microscope as argyrophilic spherules, and easily counted. The number of fibrillar centers was variable according to culture conditions. In cells cultured for 5 hr, the mean number of fibrillar centers was 1.7. After 5 days of culture, the number of fibrillar centers increased, reaching a mean value of 5.93. When thyroid cells were stimulated with thyrotropin, the number of fibrillar centers again increased to a mean value of 7.54. These results demonstrate that the relationship between fibrillar centers and NORs is not a simple proportionality: the number of fibrillar centers increases with increased cellular activity. These data imply that in active cells each NOR may pass through several fibrillar center

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00279.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Estrogen has been shown to affect ventromedial hypothalamic (VMH) nerve cell nucleoli in ovariectomized rats, by causing an increase in the number of electron‐dense aggregates associated with nucleoli. In order to characterize these nucleolus‐associated structures and other nuclear components, we examined the ultrastructure of ventromedial hypothalamic nucleoli and nuclei revealed by enzyme digestions (pepsin, RNase and DNase) in resinless thin sections. Digestion by pepsin did not cause obvious alterations in the morphology of the nucleolus or its related structures. Pepsin treatment followed by RNase, however, reduced the density of the nucleolus, while that of the nucleolus‐associated structure and other related structures remained unchanged. Conversely pepsin treatment followed by DNase, reduced the density of nucleolus‐associated and other chromatin structures, but had no effect on the density of the nucleolus. Pepsin treatment followed by RNase and then DNase treatment, reduced the density of the nucleolus and nucleolus‐associated structures. A residual nucleolus and nucleolus‐associated structure remained after this treatment. Stereo viewing of resinless sections shows that the nucleolus, its associated structures, and other related structures, are associated with fine filaments that may comprise the nuclear matrix. The nucleolus‐associated structure containing DNA may direct RNA synthesis at an increased rate in estrogen‐treated hyp

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00280.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Acetylcholinesterase (AChE) is composed of several distinct molecular forms, which are identified and partly resolved by velocity sedimentation analysis on sucrose gradients. We made the assumption that each AChE form sediments as a peak of activity with a gaussian shape in the continuous sucrose gradient. We experimentally demonstrate that the complex AChE profiles can be decomposed in gaussian distributions of separate molecular entities. We performed a high salt‐detergent extraction of AChE from mouse skeletal muscle and isolated fractions enriched in each particular from. These fractions were then submitted to a second sedimentation, to assess the stability and to further characterize each AChE form. Then, we calculated the statistical significance level of each AChE form and identified up to 9 separate molecular specifies in mouse adult muscle. These forms are the major “4 S”, “6.5 S”, “10 S”, “12 S” and “16 S” and minor molecular active components of AChE. These results suggest complex structural interactions between catalytic and non catalytic subunits of AChE and do not simply fit the tailed asymmetric globular model of AChE with

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00281.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Two microanalytical methods, electron probe X ray analysis (E P M A) and ion mass analysis (I A M) were used to study gallium incorporation in normal tissues (kidney, liver, mammary gland, bone marrow, bone tissue) and in experimental tumors. The very high sensitivity of I M A makes possible the detection of very low concentration of gallium (1 ppm) with a spatial resolution of 0.5 micron, on the other hand, E P M A of lower sensitivity (100 ppm) makes possible the relation between the gallium concentration and the ultrastructure of the cell. It was shown that gallium is concentrated in the lysosomes of both types of tissues, where it is precipitated in an insoluble form. In addition, gallium is systematically combined with phosphorus in these precipitates. These observations suggest an active intralysosomal concentrating mechanism related to the presence of local phosphatase activity.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00282.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The internalization of the yolk proteins has been investigated by electron microscopy and cytochemistry in the oocyte of the trout which stores up large quantities of yolk. The oocyte evolution has been followed for 18 months in a homogeneous group of animals. Anionic ferritin has been injected during vitellogenesis. The results indicate that as in other oocytes the yolk proteins are absorbed by coated vesicles during vitellogenesis. But unlike most other oocytes the yolk proteins are then transferred via typical endosomes to a conspicuous lysosomal compartment built up very early at the onset of the cytoplasmic differentiation of the oocyte e.i. 10 months earlier. During vitellogenesis yolk progressively accumulates in this lysosomal compartment. Injected anionic ferritin follows the same pathway of internalization. These findings indicate that in this oocyte, the whole yolk cycle presumably represents an adaptation of a general cellular activity, the receptor‐mediated endocytosis, largely amplified, sequenced and spread over several month

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00283.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The cytoplasm of the ciliated protozoan Isotricha prostoma is compartmented by a continuous fibrillar system made up of a double layer of 4 nm‐diameter filaments: the microfibrillar ecto‐endoplasmic boundary (EEB). Isolation of this structure after treatment of the cells in a buffer of low ionic strength in the presence of the detergent Triton X‐100 evidenced connections linking the two filamentous layers. One dimensional electrophoresis on SDS‐polyacrylamide gel of EEB fractions revealed several major proteins with apparent molecular weights between 11 and 23 K. Of these, two neighboring bands of MW22 and 23 K were removed from gels and used as antigens to obtain rabbit antibodies. The antiserum obtained reacted specifically with injected proteins as shown by the technique of immunological detection on nitrocellulose sheets using the peroxidase reaction product. Electron microscopy localization of the antigens with anti‐IgG coupled with colloidal gold showed significant labeling of the EEB within the cortex of Isotricha permeabilized with Triton X‐100. We hope that the 22‐23 K antiserum will prove to be a useful tool for the comparative study of other non‐actin filament syst

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00284.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

Colicins are released into the spent medium from colicinogenic cells. The pathway of release has been investigated in this study. The localization in producing cells of colicins A, E3 and of cloacin DF13 has been determined at various times after mitomycin C addition: no transient accumulation in the periplasmic space of colicinogenic E. coli K12 strains was detected by electron microscopy for any of the bacteriocins tested. Furthermore, asynchronous induction in individual cells was detected for each bacteriocin tested. These results strongly suggest that colicins, as well as cloacin DF13, do not transit through the periplasmic space before release from colicinogenic cells.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00285.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

An ultrastructural study of the pars distalis of the pituitary in Rana ridibunda specimens subjected to constant environmental conditions revealed significant structural differences which indicate a short‐time increase in the activity of gonadotrophic cells. Planimetry was used for morphometric and stereological analysis of the rough endoplasmic reticulum, Golgi complex, secretory granules and lysosomes. The presence of a vesicular endoplasmic reticulum throughout the cytoplasm of gonadotrophic cells was observed in the pituitary gland of the intact frog. After 7 days of constant environmental conditions, there was an increase in the volume density of the endoplasmic reticulum vesicles, while on the 11th day there was a slight reversal in the vesicle content that was complete the 15th day. In the hypertrophy of the endoplasmic reticulum, the larger vesicles (bigger than 0,52 micron2) play a more important role than the smaller ones (similar to the endoplasmic reticulum observed in control cells). However, the small vacuoles were also hypertrophied in relation to the control. Degranulation was also observed after 7 days of constant environmental conditions. On the 15th days, there was an increase in the numerical density of secretory granules and lysosomes compared to the control while their volume density was similar to the contro

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00286.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY

摘要:

The mesonephros of the chick embryo normally begins to regress during the second half of embryonic life. Experimental methods, such as adenohypophysis grafting, hypophysectomy or use of antithyroid drugs, which stimulate or depress the thyroid function of the embryo, modified accordingly the regressive processes occurring in the mesonephric Malpighian corpuscles, particularly at the level of the glomerular basement laminae. These results as well as the known sensitivity of the mesonephros to thyroxine and the concordance between the steps of embryonic thyroid development and the mesonephric modifications show that the thyroid normally plays a major determining role in this phenomenon.

ISSN:0248-4900    

DOI:10.1111/j.1768-322X.1984.tb00287.x

出版商:Blackwell Publishing Ltd    

年代:1984

数据来源: WILEY