Biomedical subjects

J F Dong

Publications and source records attributed to J F Dong.

23 records · Page 2Linked to original sources

PubMed1994

Tyrosine sulfation of the glycoprotein Ib-IX complex: identification of sulfated residues and effect on ligand binding.

Here, we present evidence that glycoprotein (GP) Ib alpha, one of three polypeptides that make up the GP Ib--IX complex--the receptor for von Willebrand factor (vWf) on the surface of unactivated platelets--is modified by sulfation of tyrosine residues. Only GP Ib alpha was found to incorporate 35S when the GP Ib--IX complex was immunoprecipitated from [35S]sulfate metabolically labeled L and CHO cells that express the recombinant complex. The occurrence of sulfation on tyrosine residues of the polypeptide backbone was determined by removing O- and N-linked oligosaccharides. Limited proteolytic digestion of metabolically labeled GP Ib alpha revealed that sulfated tyrosine residues are located in the 45-kDa globular region containing the vWf binding site. By mutating potentially sulfated tyrosine residues to phenylalanine and comparing the stoichiometry of sulfate incorporation of these mutants to the incorporation in wild-type GP Ib alpha, three clustered tyrosine residues--Tyr-276, Tyr-278, and Tyr-279-were identified that undergo the modification. Culturing cells in sulfate-depleted medium containing sodium chlorate and guaiacol completely inhibited GP Ib alpha sulfation but did not decrease GP Ib-IX expression on the cell surface. Similarly, transiently transfected CHO cells expressed the mutant GP Ib alpha polypeptide on their surfaces at the same levels as they expressed wild-type GP Ib alpha. These results suggest that tyrosine sulfation of GP Ib alpha has little or no effect on the synthesis, assembly, and surface expression of the GP Ib-IX complex. Nevertheless, inhibiting sulfation of GP Ib alpha reduced the binding of 125I-labeled vWf in the presence of ristocetin by up to 37%.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1994

Enhanced in vitro survival and growth of foetal human mesencephalic dopaminergic neurones on laminin and collagen: implications for cell banking.

Culture of second trimester mesencephalic cells on laminin and collagen substrata has been investigated in an attempt to ascertain the effects of these extracellular matrix components on survival and growth of central dopaminergic (DA) neurones. There were 156.8-186.4% more cells attached to laminin and collagen than poly-D-lysine 6 h post-plating. By 24 h there was statistically no significant difference in the total number of cells attached to the three substrate but in terms of cell type-specific survival the proportion of mesencephalic DA neurones surviving on laminin and collagen substrata after 7 days in culture increased significantly compared with poly-D-lysine (1.4-1.6% versus 0.4% of the total cellular population), an effect augmented by bFGF treatment, which led to levels of 2% or more, with a concomitant decrease in the proportion of attritic DA neurones. These results indicate a critical requirement for ECM proteins in the survival and growth of in vitro-propagated central DA neurones at the time of plating and throughout the culture period. They also imply survival-enhancing interactions of ECM proteins and neurotrophic factors in developmental neuronal regulation and provide paradigms for obtaining high yields of these cells for neural transplantation cell banks.

Cell Division↗

PubMed1993

Susceptibility of human foetal brain tissue to cool- and freeze-storage.

Human second trimester foetal brain tissue was stored for a period of 1-6 weeks under various conditions in an attempt to evaluate factors influencing its susceptibility (cell loss) and survivability. Post-storage viability of mesencephalon, striatum, cerebellum and occipital cortex was assessed by a protocol combining vital staining with cell density counts so that tissue viability and cell loss could be evaluated simultaneously; tissue survivability was evaluated by cell culture. A significant amount of cell loss occurred after 24 h storage at room temperature, after one week at 4 degrees C and by two weeks at -20 degrees C in all structures; storage at -196 degrees C resulted in 17-21% cell loss at the end of a 6 week period. At -20 degrees C the cryoprotective effect of 20% FCS was equivalent to that of 15% FCS + 7% DMSO combined, suggesting potential use of serum in replacement of chemical additives. The procedure for removal of DMSO was critical to cell viability and survivability: single step dilution led to 27-39% greater cell loss than slow, multi-step dilutions. In comparison to fresh, non-stored tissue, immunocytochemical characterization of in vitro propagated stored tissue revealed no changes in the populations of major constituent cell types including neurones, dopaminergic neurones, glial and fibroblast cells. These results provide information on possible conditions under which transplant tissue can be satisfactorily stored depending on the prevailing requirements.

Brain↗

PubMed1993

Direct interaction with target-derived glia enhances survival but not differentiation of human fetal mesencephalic dopaminergic neurons.

Regulation of the developing nervous system involves attraction, guidance and modification of innervating neurons by target cells through diffusible and membrane-related factors. The trophic effects from specific cell types remain to be investigated and characterized. In a series of experiments in which human fetal mesencephalic dopaminergic cells were co-cultured with target or non-target neurons or glial cells in direct or contiguous contact, we demonstrate that striatal glial cells (target-derived glia) can enhance dopaminergic neuron survival by up to 400% compared to either non-target cell co-cultures or mesencephalic controls. When in direct contact with striatal neurons, a greater proportion of dopaminergic neurons had a more differentiated morphology. The enhancement of dopaminergic neuron survival by target-derived glia appears to be mediated both by direct contact, possibly through target membrane-specific phenomena, and by diffusible substances, whereas non-target glia appear to exert the trophic effects predominantly through the latter mechanism. The finding that target neurons influence mainly dopaminergic neuron differentiation and target glia their survival indicates multiple, target cell type-specific regulation of innervating neuron development. These findings also have relevance to the establishment of neuronal cultures for neural transplantation.

Cell Communication↗

PubMed1992

Intracranial tumors in children. An analysis of 2000 cases.

Two thousand patients aged 15 years and below, who underwent surgical treatment for intracranial tumors in Beijing Tiantan Hospital from 1955 to 1989, were studied. All of the tumors in this series have been verified by operative findings and histological studies. This series accounts for 15.1% of all cases of intracranial tumors treated within the same period. The characteristics of the histological classifications, locations and clinical manifestations of the intracranial tumors in children are presented. Stresses are placed on the importance of making correct diagnoses in the early stage. Misdiagnoses had been made in 1/4 of the cases in this series before they came to our hospital, thus causing much delayed treatment in many of them. Malignant tumors make up a majority of intracranial tumors in children, and so the prognoses of intracranial tumors are poorer in children than in adults. The authors are of the opinion that adequate radiotherapy is needed after surgical intervention for many of the intracranial tumors.

Astrocytoma↗