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J Nelson

Publications and source records attributed to J Nelson.

At least 37 records · Page 2Linked to original sources
PubMed2001

Electron self-exchange kinetics in two average-valence dicopper cryptates.

Electron self-exchange rates, reported for two average-valence dicopper cryptates are, at around 10(5) M-1 s-1, at the high end of the range for small-molecule model compounds. The cross-exchange reaction rate, and those for oxidation with [Co(ox)3]3-, are consistent with an outer-sphere reaction mechanism. Despite the necessity for copper-copper bond making and breaking in the course of redox for one of the cryptates, the self-exchange rate is not decreased relative to the other cryptate, showing that this step is not rate limiting.

Bridged Bicyclo Compounds, Heterocyclic↗
PubMed2001

Unexpected and variable phenotypes in a family with JAK3 deficiency.

Mutations of the Janus kinase 3 (JAK3) have been previously described to cause an autosomal recessive variant of severe combined immunodeficiency (SCID) usually characterized by the near absence of T and NK cells, but preserved numbers of B lymphocytes (T-B+SCID). We now report a family whose JAK3 mutations are associated with the persistence of circulating T cells, resulting in previously undescribed clinical presentations, ranging from a nearly unaffected 18-year-old subject to an 8-year-old sibling with a severe lymphoproliferative disorder. Both siblings were found to be compound heterozygotes for the same deleterious JAK3 mutations: an A96G initiation start site mutation, resulting in a dysfunctional, truncated protein product and a G2775(+3)C mutation in the splice donor site sequence of intron 18, resulting in a splicing defect and a predicted premature stop. These mutations were compatible with minimal amounts of functional JAK3 expression, leading to defective cytokine-dependent signaling. Activated T cells in these patients failed to express Fas ligand (FasL) in response to IL-2, which may explain the accumulation of T cells with an activated phenotype and a skewed T cell receptor (TcR) Vbeta family distribution. We speculate that residual JAK3 activity accounted for the maturation of thymocytes, but was insufficient to sustain IL-2-mediated homeostasis of peripheral T cells via Fas/FasL interactions. These data demonstrate that the clinical spectrum of JAK3 deficiency is quite broad and includes immunodeficient patients with accumulation of activated T cells, and indicate an essential role for JAK3 in the homeostasis of peripheral T cells in humans.

Adolescent↗
PubMed2001

Novel keratin 17 mutations in pachyonychia congenita type 2.

Pachyonychia congenita type 2 is an inherited ectodermal dysplasia characterized by hypertrophic nail dystrophy and multiple pilosebaceous cysts. Focal nonepidermolytic palmoplantar keratoderma, natal teeth, and pili torti may also be present. Epithelial tissues affected in pachyonychia congenita type 2 express the keratin pair K6b/K17. Here, we report three novel heterozygous mutations in the K17 gene (KRT17A) in patients presenting with pachyonychia congenita type 2. These mutations, R94-98del (deletion of the peptide sequence RLASY) and missense mutations R94P and L95Q, are all within the 1A domain hotspot for pathogenic keratin mutations.

Base Sequence↗
PubMed2001

Enhancement of human osteoblast proliferation and phenotypic expression when cultured in human serum.

Traditionally, culture medium is supplemented with foetal bovine serum (FBS). However, in cultures of osteoblasts intended for human re-implantation, such serum presents potential risks of foreign protein contamination and transmission of viral or prion-related material, if used. We cultured human osteoblasts from 16 patients in 10% autologous human serum, 10% pooled human serum, 10% FBS or 2% Ultroser G. Non-synthetic sera were tested in both heat-treated and non-heat-treated forms. We determined cell growth and osteoblast phenotype. Cell proliferation in all types of human serum was significantly greater than in FBS. This was most marked in heat-treated autologous human serum. Cells cultured in Ultroser G had less proliferation than all other groups. The phenotypic tests showed that cells cultured in human and foetal bovine serum displayed an osteoblast phenotype, with greater protein expression in cells cultured in human serum. We conclude that culture of human osteoblasts in autologous human serum enhances cell proliferation, while maintaining an osteoblast phenotype. These findings have implications for the use of cultured osteoblasts in self-cell therapy. Human osteoblast growth is supported by autologous human serum, which allows re-implantation of cultured cells, while avoiding the risk of foreign protein carry-over with enhancement of cell proliferation.

Aged↗
PubMed2001

Health span and life span in transgenic mice with modulated DNA repair.

One way to better understand the contribution of DNA repair, DNA damage, and mutagenesis in aging would be to enhance DNA repair activity, lower DNA damage, and lower mutagenesis. Because the repair protein O6-methylguanine-DNA methyltransferase (MGMT) acts alone and stoichiometrically, the human MGMT (hMGMT) cDNA was selected to test the feasibility of enhancing DNA repair activity in transgenic mice. MGMT activity is largely responsible for ameliorating the deleterious effects of O6-methylguanine (O6mG) lesions in DNA in a direct reversal mechanism. A transgene was constructed consisting of a portion of the human transferrin (TF) promoter and hMGMT cDNA such that hMGMT is expressed in transgenic mouse brain and liver. Expression of hMGMT was associated with a significant reduction in the occurrence of an age-related hepatocellular carcinoma in male mice at 15 months of age. Longitudinal and cross-sectional studies were initiated to determine whether the reduced incidence of hepatocellular carcinoma would impact median or maximum life span. The cross-sectional study performed on 15-month-old male animals confirmed the reduced occurrence of spontaneous hepatocellular carcinoma. At 30 months of age, however, the occurrence of hepatocellular carcinoma in at least one transgenic line was similar to that for nontransgenic animals. The longitudinal study is ongoing; however, at present no significant differences in life span have been detected. Tissues expressing the MGMT transgene also displayed greater resistance to alkylation-induced tumor formation. These results suggest that transgenes can be used to direct enhanced DNA repair gene expression and that enhanced expression can protect animals from certain spontaneous and induced tumors.

Age of Onset↗
PubMed2001

A study of the anti-invasive properties of N-alpha-phthalimidomethyl-ketomethylene tripeptide-based metalloprotease inhibitors.

We have developed matrix metalloprotease (MMP) inhibitors based on synthetic peptides incorporating a non-cleavable peptide-bond isostere at the site of the putative scissile bond. These inhibitors, N-alpha-phthaloyl-Gly-psi(CO-CH2)-Leu-Tyr-Ala-NH2 (Pht-G-CH2-LYA-NH2) and N-alpha-phthaloyl-Gly-psi(CO-CH2)-Leu-Tic-Ala-NH2 (Pht-G-CH2-LTcA-NH2) were kinetically evaluated against the type IV collagenases, gelatinase A (MMP-2) and B (MMP-9), and compared with an exactly analogous chelating-based inhibitor, N-alpha-mercaptoacetyl-Leu-Tyr-Ala-NH2 (HSCH2CO-LYA-NH2). The peptide inhibitors were also tested for their anti-invasive effects on breast carcinoma cell lines using a modification of the Boyden chamber assay. Gelatin zymography was utilized to identify gelatinolytic activities present in media removed from cultured breast cancer cells. Of the two N-alpha-phthalimidomethyl-ketomethylene peptide-based inhibitors, Pht-G-CH2-LYA-NH2 proved the more effective inhibitor of MMP-2 and MMP-9 (Ki 34.27 and 45.75 microM, respectively). However, when tested against two breast cancer cell lines, T47D and MDA-MB-231, both inhibitors were able to effectively reduce tumour cell invasion through a type IV collagen matrix by up to 91.2%. Of particular interest was the observation that Pht-G-CH2-LYA-NH2 was the most potent inhibitor of invasion by the highly aggressive MDA-MB-231 cells, despite the cells' relative lack of active secreted metalloprotease activity. The results obtained from this kinetic and anti-invasive analysis of the new inhibitors suggest that compounds incorporating the N-alpha-phthalimidomethyl-ketomethylene peptide-bond isostere may have potential for development as new agents with anti-metastatic properties.

Algorithms↗
PubMed2000

Sequence and analysis of chromosome 5 of the plant Arabidopsis thaliana.

The genome of the model plant Arabidopsis thaliana has been sequenced by an international collaboration, The Arabidopsis Genome Initiative. Here we report the complete sequence of chromosome 5. This chromosome is 26 megabases long; it is the second largest Arabidopsis chromosome and represents 21% of the sequenced regions of the genome. The sequence of chromosomes 2 and 4 have been reported previously and that of chromosomes 1 and 3, together with an analysis of the complete genome sequence, are reported in this issue. Analysis of the sequence of chromosome 5 yields further insights into centromere structure and the sequence determinants of heterochromatin condensation. The 5,874 genes encoded on chromosome 5 reveal several new functions in plants, and the patterns of gene organization provide insights into the mechanisms and extent of genome evolution in plants.

Animals↗
PubMed2000

Development of laminin receptor agonists: identification of important functional residues by alanine scanning.

An antagonist of cellular adhesion and motility, acetyl-C-[S-Acm]-VIGYSGDRC-[S-Acm]-NH(2) (mEGF(33-42)), shares homology with the agonist sequence CDPGYIGSR-NH(2). It has been proposed that the latter peptide binds to the high affinity 67 kDa laminin receptor. Both peptides have equal affinities for the receptor and similar conformations have been derived for both. We have examined the importance of individual non-homologous residues with respect to receptor binding and antagonistic properties of mEGF(33-42). Alanine scanning of non-conserved residues in the N-terminal half of mEGF(33-42) caused loss of biological activity with respect to cell attachment, receptor binding and migratory response. Substitution of alanine for serine (position 6) caused loss of laminin-specific cell attachment and receptor binding activities. However, the peptide did stimulate migration suggesting that this peptide may be a non-specific stimulator of migration. In contrast, alanine substitution for the C-terminal Cys-S-Acm had no apparent effect on the attachment or receptor binding activities of the peptide but generated an agonist from the antagonist parent. Comparison of the modelled folds of the alanine containing peptides revealed the presence of significant helical content in those peptides capable of stimulating migration and suggests that a reduction in bulk in the N-terminal residues is not conducive to adopting a productive binding conformation.

Alanine↗
PubMed2000

Yellow nail syndrome presenting as non-immune hydrops: second case report.

The yellow nail syndrome is characterized by slowly growing yellow discolored nails and lymphoedema, with onset generally after puberty. We report on a newborn infant who, at 23 weeks, was found to have hydrops on antenatal ultrasonography and bilateral chylothorax at delivery. His mother has the yellow nail syndrome, with typical nail changes, and bronchiectasis. There seemed to be no other etiology for the non-immune hydrops, and this is the second documented case of the prenatal manifestation of this condition.

Adult↗
PubMed2000

Myelination in the splenium of the corpus callosum in adult male and female rats.

Previous work reported increases in the number of myelinated axons in the splenium of the rat corpus callosum between 25 and 60 days of age. In the present study, we quantified the area occupied by myelinated axons using a light microscopic point counting technique at 60, 120 and 180 days. Myelinated axons increased across these ages (p=0.001). Thus, myelination of the rat corpus callosum persists well into adulthood.

Age Factors↗
PubMed2000

Binding properties of octaaminocryptands.

Complexation and protonation equilibria were studied in aqueous solution for a new range of aminocryptand ligands, N(CH2CH2NHCH2RCH2NHCH2CH2)3N, (R = m-xylyl, p-xylyl, 2,5-furan, 2,6-pyridine) and demonstrate that stability constants for first transition series ions Co2+ to Zn2+ are relatively high. X-ray crystallography shows that the cryptands are reasonably well preorganized for complexation. The furan-spaced cryptand L6.H2O crystallizes in the rhomobohedral space group R3 (no. 148) with a = 14.645(1), b = 14.645(1), and c = 25.530(4) A, whereas the m-xylyl-spaced cryptand L4 crystallizes in the triclinic space group P1 (no. 2) with a = 9.517(1), b = 15.584(2), and c = 23.617(4) A. The highest formation constant (log beta21 = 33.07) is observed for the dicopper cryptate of a pyridine-spaced cryptand, suggesting involvement in complexation of donors from the spacer link. This pyridine-spaced host also shows good selectivity for copper(II) over zinc(II), making it a possible candidate for treatment of copper-excess pathology.

Journal Article↗
PubMed2000

The expression of membrane-associated 67-kDa laminin receptor (67LR) is modulated in vitro by cell-contact inhibition.

The interaction of cells with their substratum is an important determinant of cell behaviour, influencing attachment, proliferation, and motility. Such interactions are mediated by cell surface receptors which bind to attachment factors, like the glycoprotein laminin in basement membranes. We have previously shown that expression of the 67-kDa laminin receptor (67LR) is elevated in proliferating retinal microvasculature compared with mature, quiescent vessels. Here, we examined 67LR mRNA and protein expression in primary cultures of retinal microvascular endothelial cells (RMEC) and in the breast cancer cell-line T47D during stages of contact inhibition. In both cell types, the expression levels of 67LR mRNA and membrane-associated 67LR protein were significantly increased during the proliferative phases of monolayer formation. As the cells achieved contact inhibition, 67LR expression was reduced to comparatively low levels. Thus, the differential expression of 67LR between dividing and contact-inhibited cells may indicate a role for this receptor during proliferative processes.

Blotting, Southern↗
PubMed2000

Sentinel node biopsy and internal mammary lymphatic mapping in breast cancer.

BACKGROUND: Currently outer quadrant breast tumors are not felt to have significant drainage to the internal mammary nodal chain. We evaluated the incidence of internal mammary sentinel nodes (IMSN) found with lymphoscintigraphy for all breast quadrants. METHODS: Eighty women were prospectively studied by technitium-sulfur colloid injection, nuclear medicine imaging, and intraoperative gamma probe identification of sentinel nodes. IMSN detected were surgically removed. RESULTS: Ten of 80 ( 12%) patients had IMSN identified in addition to axillary sentinel nodes (AXSN). Four tumors were located medially, 6 (60%) were in the outer quadrants. Metastatic disease was present in 3 of 10 women. Patients with positive IMSN also had positive AXSN. CONCLUSIONS: Patients undergoing lymphatic mapping for the management of breast cancer should have radiolabelled tracer and gamma probe sentinel node identification regardless of tumor location in the breast.

Biopsy↗