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Biomedical subjects

F F Richards

Publications and source records attributed to F F Richards.

At least 19 recordsLinked to original sources
PubMed1992

Spliced leader RNA sequences of Trypanosoma rangeli are organized within the 5S rRNA-encoding genes.

The spliced leader RNA(SL RNA)-encoding genes of the salivarian New World trypanosome, Trypanosoma rangeli, are organized within the 5S rRNA tandem repeats. Each repeat contains genes encoding an SL RNA and a 5S rRNA in the same orientation of transcription. This SL-5S organization is also present in the African trypanosome, Trypanosoma vivax. A similar association of SL and 5S genes has been observed in some nematodes, but has not been described previously in trypanosomatids.

Animals↗
PubMed1992

Hyaluronidase from infective Ancylostoma hookworm larvae and its possible function as a virulence factor in tissue invasion and in cutaneous larva migrans.

During skin penetration, infective hookworm larvae encounter hyaluronic acid as they migrate between epidermal keratinocytes and through the ground substance of the dermis. A hyaluronidase would facilitate passage through the epidermis and dermis during larval invasion. Zoonotic hookworm larvae of the genus Ancylostoma were shown to contain a hyaluronidase activity that migrated on modified sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) hyaluronic acid gels with an apparent Mr of 49,000. A second form with an Mr of 87,000 was also identified. The major etiologic agent of cutaneous larva migrans, A. braziliense, was shown to have the greatest enzyme activity, hydrolyzing up to 3.3 micrograms of hyaluronic acid per h per micrograms of total parasite protein at pH 6.0, whereas A. caninum and A. tubaeforme each had much less enzyme activity. The differences in enzyme activities between species correlated with differences in the intensities of the lytic zones at 49 and 87 kDa on SDS-PAGE hyaluronic acid gels. Hookworm hyaluronidase activity exhibited a broad pH optimum between 6.0 and 8.0 and did not hydrolyze chondroitin sulfate, two features that suggest that the hookworm enzyme is more like the invertebrate leech hyaluronidase than mammalian testicular or lysosomal hyaluronidase. Larvae of A. braziliense were shown to release hyaluronidase activity and degrade radiolabeled hyaluronic acid in vitro. Gold sodium thiomalate was identified as an enzyme inhibitor. The hyaluronidase is the second major virulence factor that we have identified from infective hookworm larvae.

Ancylostoma↗
PubMed1992

Transformation of an insect symbiont and expression of a foreign gene in the Chagas' disease vector Rhodnius prolixus.

A shuttle plasmid was developed that is capable of replicating both in Escherichia coli and in Rhodococcus rhodnii, a bacterial symbiont of the Chagas' disease vector Rhodnius prolixus. We have been able to transform R. rhodnii with this plasmid, infect aposymbiotic R. prolixus with the transformed symbionts, select with the antibiotic thiostrepton, and re-isolate genetically altered symbionts from the insects following successive molts. Symbiotic bacteria are potentially valuable as vehicles for the stable introduction of foreign genes into insects with the goal of eventually altering the ability of the insect to transmit a pathogenic agent.

Animals↗
PubMed1991

Uptake of Pneumocystis carinii mediated by the macrophage mannose receptor.

Human exposure to Pneumocystis carinii is common but, in the absence of acquired or genetic dysfunction of either cellular or humoral immunity, exposure rarely leads to illness. Although alveolar macrophages can degrade P. carinii, macrophage receptors involved in P. carinii recognition have not been clearly defined. Characterization of a predominant surface glycoprotein of the high mannose type led us to investigate the role of the macrophage mannose receptor in this process. We report here that binding and uptake of cultured rat P. carinii by human and rat alveolar macrophages is reduced by 90% in the presence of competitive inhibitors of mannose receptor activity and by adherence of alveolar macrophages to mannan-coated surfaces. Further, only those COS cells transfected with the human macrophage mannose receptor complementary DNA that express surface mannose receptors bind and ingest P. carinii. These studies establish that the macrophage mannose receptor is sufficient for uptake of P. carinii and emphasize the role of the alveolar macrophage in first-line host defence against P. carinii.

Animals↗
PubMed1991

Differences in glucose transport between blood stream and procyclic forms of Trypanosoma brucei rhodesiense.

In African trypanosomes the requirements for glucose and its metabolism vary in different stages of the life cycle. Here we present evidence that cultured procyclic trypanosomes of Trypanosoma brucei rhodesiense uptake glucose against a concentration gradient in a time and dose-dependent manner. Moreover, glucose transport is completely inhibited by the sulphydryl inhibitor N-ethylmaleimide, suggesting the presence of a protein moiety as the carrier molecule. Comparison of glucose uptake in bloodstream and procyclic trypanosomes point to the possibility that different transporters may function in the 2 developmental stages. Glucose uptake by bloodstream trypanosomes requires Na+ ions and is inhibited by phlorizin, an inhibitor of Na(+)-dependent glucose transporters in mammalian cells. Conversely, procyclic trypanosomes transport glucose in a Na(+)-dependent manner, and transport is not affected by phlorizin. Finally, the putative procyclic glucose transporter has a higher affinity for glucose (apparent Km 23 microM) than the bloodstream carrier (apparent Km 237 microM).

Animals↗
PubMed1991

A new member of a family of site-specific retrotransposons is present in the spliced leader RNA genes of Trypanosoma cruzi.

A new member of a family of site-specific retrotransposons is described in the New World trypanosome Trypanosoma cruzi. This element, CZAR (cruzi-associated retrotransposon), resembles two previously described retrotransposons found in the African trypanosome T. brucei gambiense and the mosquito trypanosomatid Crithidia fasciculata in specifically inserting between nucleotides 11 and 12 of the highly conserved 39-mer of the spliced leader RNA (SL-RNA) gene. CZAR is similar in overall organization to the other two SL-RNA-associated elements. It possesses two potential long open reading frames which resemble the gag and pol genes of retroviruses. In the pol open reading frame, all three elements contain similarly arranged endonuclease domains and share extensive amino acid homology in the reverse transcriptase region. All are associated with the SL-RNA gene locus and are present in low copy numbers. They do not appear to have 5' truncated versions. All three retrotransposons are otherwise quite distinct from one another, with no significant overall amino acid homology. The presence of such retroelements inserted into the identical site within SL-RNA gene sequences in at least three evolutionarily distant trypanosomatid species argues for a functional role. Because these elements appear to have a precise target site requirement for integration, we refer to them as SL siteposons.

Amino Acid Sequence↗
PubMed1979

Expression of endogenous xenotropic retrovirus by methylcholanthrene-induced squamous cell carcinoma of the mouse respiratory tract.

As a model for human lung cancer, squamous cell carcinomas were induced by 3-methylcholanthrene in mouse tracheas which had been explanted to a subcutaneous site. The tumors that developed were examined for both ecotropic and xenotropic infectious murine leukemia virus (MuLV). From all squamous carcinomas--six out of six--a xenotropic MuLV was isolated. From some of the fibrosarcomas that occurred incidentally in our induction system, ecotropic MuLV was isolated. However, in the fibrosarcomas, no xenotropic MuLV at all was found.

Animals↗
PubMed1978

Endogenous RNA tumor viruses are activated during chemical induction of murine plasmacytomas.

Plasmacytomas are induced in BALB/c mice by the intraperitoneal injection of pristane (2,6,10,14-tetra-methylpentadecane) after a latent period of six months and more [Anderson, P. N. & Potter, M. (1969) Nature 222, 994-995]. Spleen cells mesenteric lymph node cells, thoracic lymph node cells, and peritoneal exudate cells were prepared from pristane-treated and control uninjected BALB/c mice during the course of a 10-month period, and these cell suspensions were tested for the release of infectious murine leukemia viruses. Endogenous ecotropic and xenotropic murine leukemia viruses were expressed in pristane-treated mice during the latter part of the tumor induction period, in those cell populations in which transformed plasma cells appear, namely, peritoneal exudate cells and thoracic lymph node cells. The significance of preferential expression of both ecotropic and xenotropic murine leukemia virus in target cell populations following the administration of a carcinogen is discussed in terms of the possible formation of an oncogenic variant virus.

Animals↗
PubMed1977

Expression of endogenous murine leukemia viruses during the course of a protracted immunological disorder.

Mice of the low leukemia (BALB/cJ x A/J)F1 hybrid (CAF1) strain express B-and N-tropic infectious murine leukemia virus (MuLV) after the age of 6 mo. Initation of a protracted immunological disorder, the graft-versus-host reaction (GVHR), at 7 wk of age, accelerates the induction of both these mouse-tropic endogenous viruses, and preferentially enhances the replication of B-tropic MuLV. The earlier appearance of B-tropic MuLV in a greater proportion of mice and in higher titer is thought to be casually related to the eventual development of lymphoreticular tumors in the GVHR mice, since previous studies have shown that these same tumors can be reproduced by inoculating syngeneic recipients with serially passaged GVHR extracts containing B-tropic MuLV.

Age Factors↗
PubMed1977

Structure of peptide from active site region of Escherichia coli L-asparaginase.

The L-asparagine analogue 5-diazo-4-oxo-L-[5-14C]norvaline binds irreversibly to the active site of Escherichia coli L-asparaginase. Conditions for optimal labeling in buffers containing 50% dimethylsulfoxide have been developed and kinetic parameters of the inactivation have been determined. After reduction, alkylation and subsequent degradation of the modified enzyme with alpha-chymotrypsin, the principal radioactive decapeptide of sequence Val-Gly-Ala-Met-Arg-Pro-Ser-Thr-Ser-Met was isolated. A second radioactive hexapeptide Arg-Pro-Ser-Thr-Ser-Met resulting from chymotryptic digestion of the decapeptide was also isolated. Evidence is presented for the attachment of the 5-diazo-4-oxo-L-norvaline residue to serine-9 in the decapeptide via an acid-labile linkage.

Amino Acid Sequence↗
PubMed1977

Multispecific lymphoid cell surface receptors.

When mice are sequentially immunized with two antigens to give an oligoclonal "double-binding" antibody response, there is a concomitant increase of "double-binding" cell surface receptors on their splenic lymphocytes. Competition studies suggest that the capacity to bind the two ligands, bovine pancreatic ribonuclease (EC 3.1.4.22) and a 2,4-dinitrophenyl (DNP) derivative, is a function of the same molecules. In ribo-nuclease-primed mice, an early response to bovine gamma globulin containing an average of 60 Dnp groups per molecule is the appearance of an increasing number of cells bearing surface receptors binding both ribonuclease and Dnp. Later, these double-binding cells are diluted by cells that bind Dnp, but not ribonuclease. The analogous phenomenon is observed when the two antigens are used in reverse order. While other reports suggest that there may be several different receptors in relatively undifferentiated cells from unimmunized mice, it seems likely that cells committed to antibody production carry a predominant multispecific cell surface immunoglobulin receptor.

Animals↗
PubMed1977

Role of endogenous murine leukemia virus in immunologically triggered lymphoreticular tumors. I. Development and use of oncogenic cellfree preparations serially passaged in vivo.

Cellfree extracts (CFEs) prepared from (BALB/cJ X A/J)F1 (CAF1) and (BALB/cJ X C57BL/6J)F1 (CB6F1) mice in which a graft-versus-host reaction (GVHR) has been induced are known to be oncogenic, but only after a protracted latent period (mean, 16 mo). Serial passage of such CFEs in successive generations of syngeneic mice inoculated at birth led to the development of two separate oncogenic preparations, the CA serioes in CAF, mice and the CB series in CB6F, mice, in which the mean latent period was reduced to 6 and 12 months, respectively. Both oncogenic preparations contained infectious B-tropic murine leukemia virus (MuLV) and particles with the ultrastructural characteristics of MuLV. No other kind of virus particle was seen. When these preparations were injected into infant syngeneic mice, B-tropic MuLV could be detected in the reticular tissues as early as 2 weeks thereafter. The virus persisted in the reticular tissues and was present in the lymphoreticular tumors that subsequently developed. However, if the same preparation was injected into young adult recipients, there may have been transient MuLV replication, but the virus subsequently disappeared from the reticular tissues and no lymphoreticular tumors developed. Previous experiments showed that MuLV was present in CFEs prepared from CAF, animals with the GVHR but absent in those of normal control mice. Since the lymphoreticular tumors arising in mice with the GVHR were the same as those induced by the CA and CB MuLV preparations, it was concluded that tumorigenesis in mice with the GVHR was caused by endogenous B-tropic MuLV activated by the immunologic disturbance.

Animals↗