Biomedical subjects

T E Martin

Publications and source records attributed to T E Martin.

At least 55 records · Page 3Linked to original sources

PubMed1995

The cytotoxicity of human immunodeficiency virus type 1 Rev: implications for its interaction with the nucleolar protein B23.

Human immunodeficiency virus type 1 (HIV-1) encodes several regulatory proteins, including two essential trans-activators for viral replication, Rev and Tat. Both Rev and Tat have a nucleolar targeting signal and are actually located predominantly in the nucleoli. Within the nucleoli, Rev is localized to the combined regions of the dense fibrillar (DFC) and the granular (GC) components. Tat does not colocalize precisely with any nucleolar component tested, but partly overlaps regions of the DFC and the GC. Regions of both Rev and Tat are overlapped by the distribution of the major nucleolar protein B23. Overexpression of Rev causes nucleolar ballooning and general structural deformity with aberrant accumulation of rRNAs, whereas Tat does not have that effect. B23 is markedly accumulated in those nucleoli deformed by Rev. Components of the nucleolar DFC, GC, and fibrillar center domains are not accumulated but dispersed in few small spots or larger patches within the enlarged nucleoli. Cytophotometric DNA determinations revealed that transient expression of Rev results in accumulation of G2, prophase, and mitotic cells which have failed cytokinesis, suggesting that Rev is capable of preventing or slowing the progression through mitosis. Tat, in contrast, does not affect the cell cycle. We speculate, based on these results, that Rev represses cell growth by inhibiting the transport of ribosomal proteins and preribosomal particles across the nuclear envelope and affecting the cell cycle, both of which may be related to proposed functions of B23.

Animals↗

PubMed1995

The post-transcriptional regulator Rex of the human T-cell leukemia virus type I is present as nucleolar speckles in infected cells.

The rex-encoded protein (Rex) of human T-cell leukemia virus type I (HTLV-I) is responsible for the cytoplasmic accumulation of incompletely spliced mRNAs that encode the virion structural proteins. Rex is known to be located predominantly in the cell nucleoli in transient transfections or in the isolated nuclei of HTLV-I-infected cells. However, precise location of Rex under physiological conditions has not been determined unequivocally. Here we report that Rex is primarily located as intranucleolar speckles in HTLV-I-infected cells, except for a few nucleoplasmic speckles. This is in contrast to the more diffuse nucleolar distribution of the rev-encoded protein (Rev) of human immunodeficiency virus type 1 (HIV-1), the functional homologue to Rex, in HIV-1-infected cells. Accumulation of Rev is associated with disruption of nucleolar structure and cell death, whereas Rex does not have these effects. The difference in distribution of Rex and Rev within the nucleoli may reflect the difference of toxicity toward the host cells. Involvement of the nucleolus in processing of certain mRNAs is also discussed.

Animals↗

PubMed1995

Novel nuclear ribonucleoprotein structural components in the dormouse adrenal cortex during hibernation.

Adrenocortical cell nuclei of the dormouse Muscardinus avellanarius were investigated by electron microscopic immunocytochemistry in hibernating, arousing and euthermic individuals. While the basic structural constituents of the cell nucleus did not significantly modify in the three groups, novel structural components were found in nuclei of hibernating dormice. Lattice-like bodies (LBs), clustered granules (CGs), fibrogranular material (FGM) and granules associated with bundles of nucleoplasmic fibrils (NF) all contained ribonucleoproteins (RNPs), as shown by labeling with anti-snRNP (small nuclear RNP), anti-m3G-capped RNA and anti-hnRNP (heterogeneous nuclear RNP) antibodies. Moreover, the FGM also showed immunoreactivity for the proliferation associated nuclear antigen (PANA) and the non-snRNP splicing factor SC-35. All these nuclear structural components disappeared early during arousal and were not found in euthermic animals. These novel RNP-containing structures, which have not been observed in other tissues investigated so far in the same animal model, could represent storage and/or processing sites for pre-mRNA during the extreme metabolic condition of hibernation, to be quickly released upon arousal. NFs, which had been sometimes found devoid of associated granules in nuclei of brown adipose tissue from hi-bernating dormice, were present in much higher amounts in adrenocortical cell nuclei; they do not contain RNPs and their role remains to be elucidated. The possible roles of these structures are discussed in the frame of current knowledge of morpho-functional relationships in the cell nucleus.

Adrenal Cortex↗

PubMed1994

Is the coiled body involved in nucleolar functions?

Coiled bodies (CBs) are structural constituents observed in nuclei of most eukaryotic cells. They usually occur in the nucleoplasm as well as in contact with the nucleolar surface. In this work we studied the hepatocyte nuclei of hibernating dormice in order to investigate possible modifications of CBs along the seasonal cycle. CBs were abundant during hibernation and rapidly disappeared upon arousal from hibernation. Moreover, CBs were frequently found to be integrated into the nucleolar body. Immunocytochemical analyses showed that CBs contain nucleoplasmic as well as nucleolar RNA-processing factors, suggesting an "ambiguous" role for this organelle in the nuclear functions.

Animals↗

PubMed1994

Physiologically inactive nucleoli contain nucleoplasmic ribonucleoproteins: immunoelectron microscopy of mouse spermatids and early embryos.

Physiologically inactivating or reactivating nucleoli represent a good model to investigate modifications of the nucleolar activity, which influence to a great extent the morphology of this organelle. We have studied the nucleoli of mouse spermatids during gradual inactivation, as well as those of early mouse preimplantation embryos, which undergo reactivation. In the 2-cell systems, inactive nucleoli are represented by homogeneously, finely fibrillar spherical bodies. With the aim of clarifying the composition of these nucleoli, we have analyzed them by means of immunoelectron microscopy using specific antibodies directed against nucleoplasmic snRNPs, hnRNPs, ribosomal proteins, or fibrillarin as well as by cytochemical methods for visualizing DNA and RNA. Our results indicate that RNA is present in zygote and 2-cell nucleolus precursor bodies (NPBs) as well as in 4- to 8-cell or more advanced embryo nucleoli, but not in inactive spermatid nucleoli. DNA is absent from inactive spermatid nucleoli and NPBs but is present within the nucleolus-associated chromatin and the nucleolonema of active nucleoli. The dense masses constituting the NPBs of the zygote and 2-cell embryos contain ribosomal proteins and fibrillarin but also hnRNPs and nucleoplasmic snRNPs. Of these, only fibrillarin is present in the spermatid residual nucleoli.

Animals↗

PubMed1994

Glyceraldehyde-3-phosphate dehydrogenase modifier protein is associated with microtubules in kidney epithelial cells.

After exposure of monkey kidney epithelial cells to a reduced concentration of K, a known mitogenic signal, the glycolytic enzyme glyceraldehyde-3-phosphate dehydrogenase (G3PD) is activated by a cytosolic protein whose function appears to be novel. A monospecific antibody was used as an immunoprobe to study the contribution of this G3PD modifier protein (MP) to signal transduction. Raising the extracellular Na concentration as well as lowering the K concentration of the medium increased the amount of MP in cytosol and also activated G3PD. Metabolic labeling of cells followed by preparation of detergent-soluble (cytosolic) and detergent-resistant (cytoskeletal) fractions, immunoprecipitation, and sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radiolabeled immune precipitates suggested that the protein was also associated with cytoskeleton. Depolymerization of the microtubules with colchicine or nocodazole increased cytosolic immunoreactive MP, whereas cytochalasin D had no effect. Taxol, which stabilizes microtubules, blocked the effects of colchicine or nocodazole. When tubulin, actin, and intermediate filament fractions of the cytoskeleton were prepared, blotted, and probed with specific antibodies, MP was found in the tubulin fraction. These observations suggest that MP is associated with the microtubules and can be displaced into the cytosol, wherein it could activate G3PD and thereby stimulate glycolytic production of ATP during mitogenic signal transduction.

Animals↗

PubMed1994

Immunocytochemical characterization of nuclear ribonucleoprotein fibrils in cells of the central nervous system of the rat.

Nucleoplasmic structural constituents observed in partially decondensed nuclei of the central nervous system of the rat were analyzed by postembedding immunoelectron microscopy using antibodies specifically recognizing heterogenous nuclear ribonucleoprotein (hnRNP) and small nuclear ribonucleoprotein (snRNP) complexes and DNA. Fibrogranular RNP structures (polyparticles) were found in close proximity to DNA containing fibrillar areas resulting from partial dispersion of compact chromatin. The polyparticle-type fibrils are labeled by antibodies recognizing hnRNP core proteins as well as snRNPs (Sm antigen or 70 kDa protein of U1snRNP) or the m3G-cap structure of snRNAs. These observations suggest that such polyparticle-type fibrils correspond to extended perichromatin fibrils. Partially decondensed perichromatin granules are rarely labeled by anti-snRNP or snRNA antibodies. When labeling occurs it is restricted to the periphery of the granules. However, anti-hnRNP antibodies frequently label these granules. Our results favor the idea, previously proposed for Balbiani ring granules, that perichromatin granules are formed by the folding of hnRNP containing perichromatin fibrils (polyparticles) in the process of splicing, and that mature perichromatin granules contain already spliced messenger RNA.

Animals↗

PubMed1994

Cytochemical and immunocytochemical characterization of nuclear bodies during hibernation.

Brown adipose tissue and liver of hibernating, arousing and euthermic individuals of the dormouse Muscardinus avellanarius were studies using ultrastructural cytochemistry and immunocytochemistry with the aim to investigate possible fine structural modifications of the cell nucleus during the seasonal cycle. The general morphology of brown adipocyte and hepatocyte nuclei was similar in the three experimental groups. However, three nuclear structural constituents were identified only in hibernating individuals: coiled bodies (CBs) and amorphous bodies (ABs) were observed in hepatocytes and, together with bundles of nucleoplasmic fibrils (NF), were present in brown adipocytes of hibernating dormice. In arousing animals only some structural constituents suggestive of poorly structured CBs were found. The latter showed the same immunocytochemical features as CBs of hibernating individuals, suggesting that they are disappearing CBs. A possible involvement of CBs in storing and/or processing RNA which must be rapidly and abundantly released upon arousal is discussed. ABs similarly to CBs contain RNA and nucleoplasmic ribonucleoproteins (RNPs) and could also be involved in mRNA pathways. NF do not contain nucleic acids or RNPs and seem to be composed of protein-aceous material; their functional role in the nuclear metabolism of hibernating brown adipocytes remains unclear.

Adipocytes↗

PubMed1994

The effect of a new ejection seat headbox and high G garments on head mobility during air combat.

Full coverage anti-G trousers, a chest counter pressure garment for positive pressure breathing for G tolerance, and a smaller ejection seat headbox have been developed for future agile aircraft. The hypotheses that the new headbox might improve, and that the more restrictive high G garments might compromise, pilot head mobility were tested. The RAF institute of Aviation Medicine Hawk aircraft was equipped with a wide angle video camera facing the front seat pilot. Two experimental conditions were compared to the control air combat sortie: 1. standard garments and the smaller headbox; 2. high G garments and the smaller headbox. Data were recorded from five instructor pilots during three scheduled air combat training sorties. Their helmets were marked with 10-mm white dots in a standardized pattern. Software for recording helmet dot positions from single frame video images, and a trigonometric method for calculating head rotation and translation from changes in the helmet dot positions were devised. No differences were found between headboxes or garments at the three extremes of head movements analyzed. Observed neck rotations were similar to maximal seated norms. Optimal head and neck extension is impeded by the ejection seat headbox. Pilots' head movements are not restricted during air combat at moderate G levels.

Aerospace Medicine↗

PubMed1993

Immunoelectron microscope localization of snRNP, hnRNP, and ribosomal proteins in mouse spermatogenesis.

We have studied the ultrastructural distribution of heterogeneous nuclear ribonucleoproteins (hnRNPs), small nuclear ribonucleoproteins (snRNPs), and ribosomal proteins during mouse spermatogenesis and spermiogenesis by means of specific antibodies and immunocytochemistry. All the above components were detectable from primary spermatocytes until the spermatid elongation phase, when the RNA synthetic activity is known to cease. Ribosomal protein (P1/P2 and L7) labeling disappeared as early as during the acrosome phase, and nucleoli were no longer labeled even during the cap phase. The nucleoplasmic structures labeled with the different anti-nucleoplasmic RNP immunoprobes corresponded, until the acrosome phase, to those previously observed as targets of the same antibodies in the nucleoplasm of somatic cell nuclei. Clusters of interchromatin granules of spermatocyte and early spermatid nuclei exhibit some labeling for hnRNP when compared with nuclei of Sertoli cells or previously analyzed liver or tissue culture cells, where these structural constituents usually remain weakly labeled or unlabeled. In spermatids in step 10, another type of nuclear granule, resembling perichromatin granules, but occurring in aggregates, can be observed. These structural constituents were labeled with antibodies recognizing nucleoplasmic snRNP antigens and therefore suggesting a non-nucleolar origin of these granules. Finally, we have observed nucleoplasmic areas of fibrogranular material, occurring only in primary spermatocytes. These components were labeled with anti-ribosomal protein antibodies but did not contain either hnRNPs or snRNPs.

Acrosome↗

PubMed1993

Resolving the casualty evacuation conflict.

One of the most contentious issues surrounding the prehospital management of the injured is the decision to stabilize on site or to rapidly evacuate the patient. Although there are vociferous proponents for both views, there appears to be little thought given to the rationalization of these decisions, and the subject has only merited lip-service in previous texts. Treatment choices and decisions in the prehospital environment are notoriously difficult to make. The doctor, unlike ambulance paramedics, does not necessarily work to didactic protocols and, if suitably trained, is at liberty to commence advanced resuscitation procedures at the roadside. However, these may be time consuming and, to be of greatest benefit to the patient, a fine balance between resuscitation and evacuation must be drawn. This paper aims to discuss some of the key issues which need to be considered in the prehospital scenario, such as treatment triage, evacuation priorities, mode of transportation and hospital destination. The end result must be to eliminate the medical 'bottleneck' and to afford early and appropriate definitive care to those in most need.

Aircraft↗

PubMed1992

Cytokeratin reorganization induced by adenosine diphosphate in kidney epithelial cells.

Exogenous adenosine diphosphate (ADP), the most potent mitogen for nontransformed African green monkey kidney epithelial cells of the BSC-1 line, rapidly alters the appearance of the cell monolayer. Examination of the cells with indirect immunofluorescence using monoclonal antibodies reveals a considerable reorganization of cytokeratin filaments without a major change in the pattern of microtubules or microfilaments. In untreated confluent cells, cytokeratin filaments are predominantly confined to a star-like spot in the perinuclear area, but these can be seen to begin to spread within 2 min after addition of ADP. The effect is particularly notable using anti-cytokeratin 8 antibodies. At 6 h this process is complete and produces a well-developed filamentous network throughout the cell. By 12 h, the network appears to collapse, so that the filaments again form a spot in the perinuclear area, a process that is complete by 24 h. Immunoblotting of total cellular proteins reveals no apparent alterations in the amounts of several species of cytokeratins, including cytokeratin 8 and 18, at 3 or 24 h after exposure to ADP. Other purine and pyrimidine nucleotides which do not stimulate DNA synthesis in these cells fail to alter cytokeratin organization, and there is no apparent alteration in the distribution of vimentin, another intermediate filament protein. The rapid ADP-induced cytokeratin reorganization appears to coincide with the induction of early growth-response gene transcription in these cells and may be correlated with the capacity of ADP to subsequently initiate DNA synthesis. This dramatic and reversible cytokeratin reorganization immediately after exposure to ADP may be an important step in the mitogenic signal transduction pathway.

Adenosine Diphosphate↗

PubMed1992

Ribonucleoprotein components of root meristematic cell nuclei of the tomato characterized by application of mild loosening and immunocytochemistry.

Immunocytochemistry and hypotonic-formaldehyde fixation have been used to study the extranucleolar ribonucleoprotein (RNP) constituents of the nucleus of tomato root meristematic cells. The study of the distribution of small nuclear uridine-rich RNPs (snRNP) by means of a monoclonal anti-Sm antibody recognizing a 29-kDa protein in plants, after standard fixation, shows a preferential labeling of the perichromatin region and a lower labeling of the interchromatin space. These results suggest that in the tomato there is a perichromatin region similar to that of animal cells, in which much of the nonnucleolar transcription and splicing takes place. In hypotonic-formaldehyde-detergent-fixed nuclei, fibrogranular polyparticles have been visualized reacting with anti-snRNP antibody. These structures are frequently associated with filaments of extended chromatin characterized by their reaction with an anti-DNA monoclonal antibody.

Antibodies, Antinuclear↗

PubMed1992

Al Jubail--an aeromedical staging facility during the Gulf conflict: discussion paper.

During the latter half of 1990 the Royal Air Force established a medical evacuation chain in support of the British First Armoured Division during Operation Granby (known as Operation Desert Storm in the USA). Medical contingency plans, formulated prior to embarkation from the UK, foresaw the need for five aeromedical staging facilities sub-deployed throughout the east of the Arabian Peninsula. The early days of the deployment found personnel busy with the construction of tented and hardened facilities and with the establishment of local operating procedures. Many problems were initially encountered, especially with supply, communications and in co-ordinating with collaborating coalition and host nation units. Nevertheless, progress was rapid and non-combatant operations were started within days of arrival. As the ground offensive became more imminent, training took on a sense of urgency. Advanced first aid techniques were taught to all non-medical staff, whereas doctors, nurses and paramedical personnel were taught ACLS and ATLS skills. All studied field hygiene, the hazards of nuclear, chemical and biological warfare, casualty handling, battle psychology and the intricacies of loading and unloading various types of aircraft. By the start of the ground phase of the war the British evacuation chain was fully operational and capable of treating and transferring hundreds of casualties per day. In the event, only about 850 patients were transported down the evacuation chain during the conflict, and less than 10% of these were battle casualties. This paper presents an overview of the British aeromedical evacuation system and discusses, in more detail, the establishment and operation of the busiest aeromedical staging facility at Al Jubail in the Eastern Province of Saudi Arabia.

Aircraft↗

PubMed1991

Nucleic acid binding characteristics of group A/B hnRNP proteins.

hnRNP proteins are primarily defined by their specific sedimentational, reconstitutional, and extraction properties and are presumed to be RNA binding. However, it is not clear whether all these proteins have RNA binding capabilities. Recently, using two monoclonal antibodies, fA12 and AC88, we reported that the abundance of a subclass of the highly basic A/B hnRNP proteins was specifically down regulated during terminal differentiation of human and murine cells in vitro. In this report we have examined the nucleic acid binding characteristics of this subclass and other members of the A/B hnRNP proteins in vitro. All members of class A/B hnRNP proteins appear to have similar but not identical nucleic acid binding characteristics. However, the subclass of proteins recognized by AC88 and fA12 exhibit stronger binding affinities and are shown to be highly selective in their binding to RNA vs DNA in vitro. These proteins also preferentially bind poly(U) RNA, suggesting that in vivo they may bind effectively to uridine rich motifs critical in pre-mRNA processing.

Animals↗

PubMed1991

Immunoelectron microscopic localization of small nuclear ribonucleoproteins during bovine early embryogenesis.

Small nuclear ribonucleoproteins (snRNPs) were localized using human autoimmune or monoclonal anti-snRNP antibodies and ultrastructural immunocytochemistry in early preimplantation bovine embryos before and at transcription onset. Bovine cleavage stages up to 16-cell embryos were obtained either by culture of in vitro-fertilized ovarian oocytes or by isolation at slaughter of embryos fertilized and developed in vivo. Before transcription onset, up to the four-cell stage, diffuse labeling of nucleoplasm was detected, whereas cytoplasm labeling remained low. At the transcription onset, labeling of all eight-cell embryo nuclei was markedly concentrated at the borderline of already formed, condensed chromatin aggregates, where it was associated mainly with perichromatin fibrils. The condensed chromatin blocks revealed by several different staining methods were more prominent than is the case in most somatic cells. The degree of chromatin condensation and the pattern of its distribution differed between in vivo- and in vitro-produced eight-cell embryos: the in vitro embryos showed a higher degree of chromatin condensation and a peripheral distribution of chromatin blocks. A relation of this observation to the developmental potential of cow embryos is suggested. In two- and four-cell embryos, intensive labeling was seen in interchromatin granules, which, in their turn, were often seen in close proximity to the nucleolus precursor bodies, or in the four-cell stage were interconnected to them. No labeling was ever seen, using antibodies specific for the snRNP Sm antigen, in nucleolar precursor bodies during embryonic nucleologenesis nor in the resulting nucleoli. There was some incidental labeling of the large central vacuole appearing at the beginning of the nucleolus precursor body transformation, testifying the nucleoplasmic origin of this entity.

Animals↗

PubMed1991

Immunoelectron microscopic localization of estrogen receptor on pre-mRNA containing constituents of rat uterine cell nuclei.

The localization and quantitative changes of estradiol receptor (ER) were studied by means of immunogold-electron microscope methods using a polyclonal antibody directed against an amino acid sequence representing the DNA binding site of ER, a monoclonal antibody against hnRNP core protein, and anti-DNA antibody. The uteri of normal rats in estrus and those of ovariectomized females were used. Ovariectomized rats were studied 21 days after surgery at different times after the injection of normal saline or estradiol-17 beta. The density of labeling was measured in interchromatin space, compact chromatin, nucleolus, cytoplasm, and background of epithelial cells, muscle cells, and fibroblasts. In the three types of cells ER was found mainly on extranucleolar ribonucleoprotein (RNP) fibrils. In epithelial and muscle cells the nucleolus was labeled but compact chromatin was not labeled. In epithelial cells there was a low but significant labeling of the cytoplasm. Fibroblasts exhibited a low labeling of the compact chromatin. Ovariectomy did not change these distributions. The estradiol injection increased labeling in all compartments of epithelial and muscle cells but decreased the labeling of compact chromatin of fibroblasts. These results show: (a) that ER is mainly nuclear but it is also present in the cytoplasm, (b) that ER binds to the nuclear particles containing newly synthesized RNA, and (c) that the binding to RNPs does not block the DNA binding domain of the ER.

Animals↗

PubMed1990

Immunoelectron microscopical visualization of ribonucleoproteins in the chromatoid body of mouse spermatids.

The chromatoid body (CB), a cytoplasmic organelle present only in germ cell line, was studied at the electron microscopic level in mouse spermatids using cytochemical techniques and specific antibodies directed against sn-RNPs, hnRNPs, and ribosomal proteins. We found that specific staining for DNA as well as the use of monoclonal anti-DNA antibodies show a complete absence of DNA in the CB. The CB remains stained, however, after the application of the ethidium bromide-PTA technique, suggesting the presence of RNA within this organelle. snRNP as well as hnRNP proteins are demonstrated within the CB by means of specific monoclonal or polyclonal antibodies, especially during earlier spermiogenic stages. Monoclonal antibodies directed against the large ribosomal subunit proteins P1/P2 detect these antigens on the CB essentially along the internal threads of dense fibrillar material. Our findings suggest that the CB may function as a source of mRNA and/or of its partially processed precursors during the late stages of spermiogenesis, when the spermatid nucleus becomes gradually inactive.

Animals↗