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Biomedical subjects

D Wilkinson

Publications and source records attributed to D Wilkinson.

At least 271 records · Page 15Linked to original sources
PubMed1991

Patterning the vertebrate head: murine Hox 2 genes mark distinct subpopulations of premigratory and migrating cranial neural crest.

The structures of the face in vertebrates are largely derived from neural crest. There is some evidence to suggest that the form of the facial pattern is determined by the crest, and that it is specified before migration as to the structures that is is able to form. The neural crest is able to control the form of surrounding, non-neural crest tissues by an instructive interaction. Some of this cranial crest is derived from a region of the hindbrain that expresses Hox 2 homeobox genes in an overlapping and segment-restricted pattern. We have found that neurogenic and mesenchymal neural crest expresses Hox 2 genes from its point of origin beside the neural plate, during migration and after migration has ceased and that rhombomeres 3 and 5 do not have any expressing neural crest beside them. Each branchial arch expresses a different combination or code of Hox genes in a segment-restricted way. The surface ectoderm over the arches initially does not express Hox genes, and later adopts an expression pattern that reflects that of neural crest that has come to underlie it. We suggest that initially the neural plate and neural crest are spatially specified, while the surface ectoderm is unpatterned. Subsequently some positional information could be transferred to the surface ectoderm as a result of an interaction with the neural crest. Given that the role of the homologous genes in insects is position specification, and that neural crest is imprinted before migration, we suggest that Hox 2 genes are providing part of this positional information to the neural crest and hence are involved in patterning the structures of the branchial arches.

Animals↗
PubMed1991

Retinoic acid causes abnormal development and segmental patterning of the anterior hindbrain in Xenopus embryos.

Retinoic acid is a very potent teratogen and has also been implicated as an endogenous developmental signalling molecule in vertebrate embryos. One of the regions of the embryo reliably affected by exogenously applied RA is the hindbrain. In this paper, we describe in detail the hindbrain of Xenopus laevis embryos briefly treated with various levels of RA at gastrula stages. Such treatments lead to development of embryos with loss of anterior structures. In addition, RA has a general effect on rhombomere morphology and specific effects on the development of the anterior rhombomeres. This effect is demonstrated using neurofilament antibodies, HRP staining and in situ hybridisation using a probe for expression of the Xenopus Krox-20 gene. Anatomically it is evident that the development of the hindbrain normally anterior to the otocyst (rhombomeres 1-4) is abnormal following RA treatment. Sensory and motor axons of cranial nerves V and VII form a single root and the peripheral paths of V and VII and IX and X are also abnormal, as is the more anterior location of the otocyst. These anatomical changes are accompanied by changes in the pattern of expression for the gene XKrox-20, which normally expresses in rhombomeres 3 and 5, but is found in a single band in the anterior hindbrain of treated embryos which standardly fail to generate the normal external segmental appearance. The results are discussed in terms of both the teratogenic and possible endogenous roles of RA during normal development of the central nervous system. We conclude that low doses of RA applied during gastrulation have specific effects on the anterior Xenopus hindbrain which appear to be evolutionarily conserved in the light of similar recent findings in zebrafish.

Animals↗
PubMed1990

Knob-independent cytoadherence of Plasmodium falciparum to the leukocyte differentiation antigen CD36.

The survival of Plasmodium falciparum-infected erythrocytes is enhanced by the sequestration of mature trophozoites and schizonts from the peripheral circulation. Cytoadherence of infected erythrocytes in vivo is associated with the presence of knobs on the erythrocyte surface, but we and others have shown recently that cytoadherence to C32 melanoma cells may occur in vitro in the absence of knobs. We show here that a knobless clone of P. falciparum adheres to the leukocyte differentiation antigen, CD36, suggesting that binding to CD36 is independent of the presence of knobs on the surface of the infected erythrocyte. This clone showed little cytoadherence to immobilized thrombospondin or to endothelial cells expressing the intercellular adhesion molecule 1. Furthermore, an Mr approximately 300-kD trypsin-sensitive protein doublet was immunoprecipitated from knobless trophozoite-infected erythrocytes. Finding a P. falciparum erythrocyte membrane protein 1 (PfEMP1)-like molecule on these infected erythrocytes is consistent with a role for PfEMP1 in cytoadherence to CD36 and C32 melanoma cells.

Animals↗
PubMed1990

Myelin autoreactivity in multiple sclerosis: recognition of myelin basic protein in the context of HLA-DR2 products by T lymphocytes of multiple-sclerosis patients and healthy donors.

A panel of 20 human myelin basic protein (hMBP)-specific T-lymphocyte lines was generated from the peripheral blood of eight multiple sclerosis (MS) patients and two healthy donors, most of them expressing the HLA-DR2 haplotype, which is associated with an increased susceptibility to MS. Using HLA-DR gene-transfected mouse L-cell lines as antigen-presenting cells, we established that of the 20 hMBP-specific T-lymphocyte lines, 7 were restricted by the DR2a gene products of the DR2Dw2 haplotype. Four T-cell lines recognized hMBP in the context of the DR2b products of the DR2Dw2 haplotype. DR2b-restricted T-cell responses were demonstrable only in T-cell lines derived from MS patients. The hMBP epitopes presented by the DR2a heterodimer were mapped to peptides covering amino acid residues 1-44, 76-91, 131-145, or 139-153 and to a region spanning the thrombin-cleaved bond at Arg130-Ala131. DR2b-restricted T-cell lines recognized epitopes within amino acids 80-99 and 148-162. Peptide 139-153 was also presented in the context of HLA-DR1 molecules. Our data show that (i) in MS patients both the DR2a and DR2b products of the DR2Dw2 haplotype function as restriction elements for the myelin autoantigen hMBP, (ii) the DR2a molecule presents at least five different epitopes to hMBP-specific T lymphocytes, and (iii) anti-hMBP T-cell lines derived from individual donors can differ in their antigen fine specificity as well as in their HLA restriction.

Adult↗
PubMed1990

Human T cell responses to human papillomavirus type 16 L1 and E6 synthetic peptides: identification of T cell determinants, HLA-DR restriction and virus type specificity.

Four T cell determinants in the major capsid protein of human papillomavirus (HPV) type 16 L1 and one in the E6 protein associated with cellular transformation were defined using synthetic peptides to stimulate peripheral blood mononuclear cells from asymptomatic individuals. HLA-DR restriction was defined using murine L cells transfected with HLA-DR genes to present antigen. Responses to two of the five determinants by T cell lines and clones were shown to be specific for HPV-16 based on the lack of cross-recognition of the corresponding sequences of other known papillomavirus sequences (types 1a, 5, 6b, 8, 11, 18 and 33). The T cells raised against two of the other peptides cross-reacted with corresponding peptides from other strains to varying extents, depending on their structural homology. The implications of these results regarding the prevalence of HPV-16 infection in the population and the possible diagnostic role of these responses in papillomavirus infection is discussed.

Amino Acid Sequence↗
PubMed1990

The application of isotope limb blood flow measurement to diagnostic problems in vascular surgery.

A new method of limb blood flow measurement has been developed; normal flow is 10-22 ml/100 ml of tissue/min and flow to limbs with claudication is 1.8-2.3. Does this technique help to deal with diagnostic problems in vascular surgery? Twenty-five patients presented with exercise-induced leg pain. Twelve had a convincing history of claudication but seven of these had palpable pedal pulses, the other five had normal Doppler ratios. Of 13 with a poor history six had absent pulses; of the other seven with palpable pulses, two had abnormal and five had normal Doppler ratios. All 25 patients have had blood flow to both legs measured. For the five with a poor history, palpable pulses and normal Doppler ratios: (Table: see text). Twelve had reduced flows consistent with claudication (less than 8 ml/100 ml of tissue/min); 10 of these have undergone arteriography which demonstrated significant vascular disease, one had surgery to rheumatoid toes deferred and one refused further investigation. Of 13 with normal flows nine have been found to have significant orthopaedic problems affecting spine, hips or knees, the other four have all had normal arteriograms. In every case the history, signs or Doppler ratios were potentially misleading, but all cases of significant arterial disease were detected. It is cheap, readily available and effectively selected cases for referral or arteriography.

Gamma Cameras↗
PubMed1989

Vectors permitting visual monitoring of simple transposition events.

The construction and use of two novel transposon(Tn)-delivery vectors is described. These vectors carry Inc.W or Inc.N broad-host-range transfer functions cloned next to the narrow-host-range replicon of pBR329. The host specificities of pSLX10 and pSLX23 both complement and extend the host specificities of existing Tn delivery vectors. Plasmids pSLX10 and pSLX23 were shown to transfer at high frequency in intergeneric matings. The lux genes which are present on each vector permit the visual monitoring of transconjugants which have retained a Tn element, but are devoid of plasmid molecules. pSLX10 and pLSX23 were efficiently used to generate a range of auxotrophic mutants in various strains of Pseudomonas as well as to clone genes from Serratia liquefaciens. These vectors may have general applicability to identify and clone genes in a wide range of Gram-negative bacteria.

Bacterial Proteins↗
PubMed1989

Cotransfection of ICAM-1 and HLA-DR reconstitutes human antigen-presenting cell function in mouse L cells.

The initiation of a specific immune response is believed to require not only activation through antigen-specific receptors on T cells and B cells but also antigen-independent interactions between accessory molecules. One such molecule is LFA-1, which enhances the avidity of interactions between T cells and antigen-presenting cells, and is possibly involved in signal transduction across the T-cell membrane. Intercellular adhesion molecule-1 (ICAM-1), a surface glycoprotein of relative molecular mass (Mr) 80,000-110,000, has been defined as a ligand for LFA-1, and has been shown to participate in the interaction between T cells and monocytes. The determination of the precise contribution of such accessory molecules to antigen presentation, however, is complicated by the need to analyse against a background of multiple molecular interactions. We have investigated the role of LFA-1/ICAM-1 interactions in antigen presentation directly by quantifying the contribution of ICAM-1 expression to T-cell stimulation using L-cell transfectants that co-express ICAM-1 and HLA-DR. In the case of transfectants expressing modest levels of HLA-DR, co-expression of ICAM-1 is critical for effective HLA class II-restricted and allospecific T-cell activation, pointing to an important role for ICAM-1 in the induction of T-cell responses.

Animals↗
PubMed1989

Plasma eicosanoids, platelet function and cold sensitivity.

As abnormal eicosanoid (prostaglandin) metabolism has been suggested as a factor in the aetiology of vasospastic diseases we have measured levels of stable eicosanoid metabolites using a radioimmunoassay in 30 normal subjects and 31 patients with Raynaud's phenomenon. There were 13 patients with primary Raynaud's, ten with Raynaud's secondary to scleroderma and eight men with vibration white finger (VWF) disease. We have also measured platelet aggregation to adenosine diphosphate (ADP), collagen and adrenaline in 19 normal subjects, 22 patients with primary Raynaud's, 12 with Raynaud's secondary to scleroderma and 14 men with VWF. When compared with our normal subjects, patients with VWF have an elevated thromboxane B2 level, with a normal 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) level. Their platelets are less sensitive to ADP and collagen. Patients with primary and secondary Raynaud's have elevated thromboxane B2 levels but this is much more marked in the secondary group. Patients with primary Raynaud's have a normal 6-keto-PGF1 alpha level but in patients with secondary Raynaud's the 6-keto-PGF1 alpha level is markedly raised. The platelets from both groups are more sensitive to ADP and collagen and this is more marked in the secondary group. Whether these phenomena are a cause or an effect of vasospasm remains unknown.

6-Ketoprostaglandin F1 alpha↗