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Biomedical subjects

S Chang

Publications and source records attributed to S Chang.

At least 235 records · Page 13Linked to original sources
PubMed1995

BamHI and HindIII repetitive DNA families in the rice genome.

In this paper we describe a novel method of cloning representative members of different repetitive DNA families based on the screening of a rice (Oryza sativa) genomic library using DNA from different C0t fractions as probes. Two genomic clones, which represent two different repetitive DNA families in rice, were isolated by this method and have been characterized. Their nucleotide sequences, copy numbers, distributions in major rice genome types, methylation patterns, and chromosomal localizations were determined.

Base Sequence↗
PubMed1995

Death certificates: an efficient source for ascertainment of Creutzfeldt-Jakob disease cases.

Case ascertainment for an epidemiologic study of Creutzfeldt-Jakob disease (CJD) can be difficult. This report investigates the efficiency of various sources of case ascertainment for CJD. Cases were identified utilizing neuropathologists, hospitals and death certificates from 11 targeted states. For the period of 1986-1988, 247 death certificates indicating a diagnosis of CJD were obtained. Only 26 potential cases were identified without death certificates. The proportion of neuropathologically confirmed cases identified by death certificates only, i.e., which were not identified through any other source, was 42%. Furthermore, 80% of all the neuropathologically confirmed cases were ascertained utilizing death certificates as a source. Of the remaining 20%, 7% were ascertained through neuropathologists only, 10% through hospitals only, 1.5% through a combination of hospitals and neuropathologists, and 1.5% through another source. The false-positive rate for death certificates with neuropathology (which may have been performed after the death certificate was filled out) was estimated to be 8.3%. The results indicate that death certificates were by far the most efficient source for initial ascertainment of potential CJD cases to be followed by verification of diagnosis.

Creutzfeldt-Jakob Syndrome↗
PubMed1995

Determining priorities for family physician education in substance abuse by the use of a survey.

As the initial stage in developing a curriculum to assist family physicians to diagnose and manage alcohol abuse in their practices, questionnaires were mailed to a selected group of family physicians. A total of 117 physicians (34%) completed the questionnaire. The majority of physicians (70.1%) reported that fewer than 10% of their caseload experienced alcohol-related problems. Most physicians (59.3%) did not use any of the standard diagnostic instruments but reported that screening and detection was the most challenging alcohol-related problem along with patient management. The questionnaire identified a number of areas that could be used in the development of educational strategies to increase the expertise of primary care physicians in the diagnosis and management of alcohol-related problems.

Canada↗
PubMed1994

Differential regulation of proto-oncogenes c-jun and c-fos in T lymphocytes activated through CD28.

The T cell surface molecule CD28 binds to ligands on accessory cells and APCs, playing an important costimulatory role in the response of T cells to Ags. Our knowledge of the intracellular signaling pathways coupled to this receptor is incomplete. In addition to activation of phospholipase C gamma 1, ligation of this receptor also seems to activate a calcium-independent, CD28-specific pathway. In this paper, we report that cross-linking of CD28 (but not CD2, CD5, LFA-1, or CD7) leads to an elevation of c-jun mRNA, with only minimal activation of c-fos expression. CD28-dependent induction of c-jun expression requires protein tyrosine kinase activity, but does not depend on activation of a phorbol ester-responsive protein kinase C or elevation of cytosolic calcium. Furthermore, CD28-dependent elevation of c-jun mRNA does not appear to be mediated at the level of mRNA stability. A mechanism is suggested whereby expression of c-jun and junB, in the absence of members of the fos family, can prevent inappropriate activation of T cells caused by ligation of CD28 in the absence of a specific antigenic stimulus.

Base Sequence↗
PubMed1994

Hepatic clearance of chylomicron remnants in mice lacking apoprotein E.

Control and apoprotein E-deficient mice generated by gene targeting in embryonic stem cells were fed a fat load containing 3H-labeled retinol and the absorbed radioactivity present in the plasma, liver, and carcass measured 6 h later. The radioactivity in the plasma of the apoprotein E-deficient mice was several fold higher than in control animals, but it accounted for less than 1/5 of the absorbed radioactivity. In both groups of animals most of the absorbed radioactivity was recovered in the livers. These findings indicate that in apoprotein E-deficient mice chylomicron remnants can be taken up by the liver by a process that does not require the mediation of apoprotein E.

Animals↗
PubMed1994

Rin, a novel cell-surface protein that labels reticular neurons early in chick neurogenesis.

Rin is a large cell-surface glycoprotein that we have recently purified from chick brain, with a molecular weight of approximately 200 kD. Protein microsequence obtained from immunopurified rin does not match any sequences in the Genbank data base. Based on the sequence information and on its localization in the early chick embryo, rin is a novel cell-surface protein. Rin is expressed on the surface of many, but not all, axons in the developing chick nervous system. In the chick hindbrain, rin is expressed on reticular neurons, the first neurons to extend axons within the brain. Cranial motoneurons, which extend axons just a few stages later, do not express rin. Rin-positive axons pioneer the caudal section of the medial longitudinal fasciculus. The very first rin-positive axons that reach the floorplate do not enter the floorplate, but remain ipsilateral. Some of the next immunopositive axons to reach the floorplate do cross the midline, often with an alteration in trajectory, and often extending within the floorplate for some distance before reaching the other side. The failure of the very first rin-positive axons to cross the floorplate, and the changes in trajectory observed when the next axons extend onto the floorplate, suggests that early differentiating neurons cross the midline with some difficulty.

Amino Acid Sequence↗
PubMed1994

The molecular cloning and characterization of potential chick DM-GRASP homologs in zebrafish and mouse.

A full-length zebrafish cDNA clone and a partial mouse cDNA clone similar to chick DM-GRASP were isolated and analyzed. The nucleotide sequence of the full-length zebrafish clone shares 54% identity, and predicts 39% amino acid identity, with chick DM-GRASP. The partial mouse clone shares 76% nucleotide identity, and predicts 76% amino acid identity, with chick DM-GRASP. The predicted proteins encoded by both of these clones exhibit conserved structural domains that are characteristic of the chick protein. These features may identify them as a distinct subfamily within the immunoglobulin superfamily of cell adhesion molecules. Expression of the zebrafish DM-GRASP protein is similar to chick DM-GRASP and is principally restricted to a small subset of developing sensory and motor neurons during axonogenesis. Zebrafish DM-GRASP expression was temporally regulated and limited to specific axon domains. This regional expression correlated with fasciculated axon domains. These results suggest that the zebrafish and mouse cDNA clones represent the respective fish and mammalian homologs of chick DM-GRASP. The highly selective expression of zebrafish DM-GRASP suggests that it is involved in the selective fasciculation and guidance of axons along their normal pathways.

Activated-Leukocyte Cell Adhesion Molecule↗
PubMed1994

Carbonaceous components in the comet Halley dust.

Cometary grains containing large amounts of carbon and/or organic matter (CHON) were discovered by in situ measurements of comet Halley dust composition during VEGA and GIOTTO flyby missions. In this paper, we report the classification of these cometary grains by means of cluster analysis, discuss the resulting compositional groups, and compare them with substances observed or hypothesized in meteorites, interplanetary dust particles, and the interstellar medium. Grains dominated by carbon and/or organic matter (CHON grains) represent approximately 22% of the total population of measured cometary dust particles. They usually contain a minor abundance of rock-forming elements as well. Grains having organic material are relatively more abundant in the vicinity of the nucleus than in the outer regions of the coma, which suggests decomposition of the organics in the coma environment. The majority of comet Halley organic particles are multicomponent mixtures of carbon phases and organic compounds. Possibly, the cometary CHON grains may be related to kerogen material of an interstellar origin in carbonaceous meteorites. Pure carbon grains, hydrocarbons and polymers of cyanopolyynes, and multi-carbon monoxides are present in cometary dust as compositionally simple and distinctive components among a variety of others. There is no clear evidence of significant presence of pure formaldehyde or HCN polymers in Halley dust particles. The diversity of types of cometary organic compounds is consistent with the interstellar dust model of comets and probably reflects differences in composition of precursor dust. Preservation of this heterogeneity among submicron particles suggests the gentle formation of cometary nucleus by aggregation of interstellar dust in the protosolar nebula without complete mixing or chemical homogenization at the submicron level.

Astronomy↗
PubMed1994

Transcription factor expression is induced by axonal stimulation and glutamate in the glia of the developing optic nerve.

Recent experiments have demonstrated that stimulation of the developing optic nerve affects several glial cell characteristics, such as ionic fluxes and cell proliferation. This investigation asked if transcription factor expression may be another stimulation-dependent process in the glia of the developing optic nerve. In unstimulated optic nerves, an antibody to c-fos-related antigens demonstrated positive cell body staining at postnatal days (P) 2, 7, 14, and 60. This nuclear staining was most prominent at early postnatal ages, although young adult (P60) optic nerves showed occasional positive cells. To demonstrate the inducibility of transcription factor antigens, optic nerves from P7 animals received intermittent 15-20 Hz electrical stimulation for 5-15 min. Two hours after this stimulation, an increased number of immunoreactive cells for c-fos-related antigens, c-jun, and NGFI-A was demonstrated. Additionally, optic nerves were exposed for 5-30 min to a solution of 300 microM glutamate, latter maintained in a glutamate-free solution for 2 h, and then quickly frozen. Glutamate-treated nerves showed an increased expression of c-fos-related antigens compared to control nerves. No c-fos increase was seen in the absence of calcium. Expression of c-fos or NGFI-A occurred in cells that were S-100 positive, and most likely represented type 1 astrocytes. These studies indicate that developing (P7) optic nerves show a baseline expression of c-fos-related antigens, c-jun and NGFI-A. Stimulation through electrical nerve stimulation or glutamate results in an increased expression of these transcription factors.

Action Potentials↗
PubMed1994

Directed replacement of mt A by mt a-1 effects a mating type switch in Neurospora crassa.

To test the functions of a mating type genes, we developed an efficient strategy to select transformants of Neurospora crassa in which resident A mating type DNA was replaced by cloned DNA from the mt a idiomorph. Cloned a idiomorphic DNA could specify all functions, including fertility, of a mating type, but only when it replaced A DNA at the mating type locus. Only the mt a-1 region of the a idiomorph was necessary in order to specify a mating type. Gene replacement events involved the homologous sequences flanking the unique mating type idiomorphic DNA, resulting in apparently isogenic a and A strains. These isogenic strains were fertile when crossed with one another, indicating that no determinants outside the transforming DNA are necessary for fertility as a and that no host sequences of A strains interfere with fertility as a. One a replacement strain bore a duplication of the transforming mt a-1 and hph DNA. The duplication strain had unexpected properties. Although mating type segregated 1:1 in crosses of this strain to A, the duplicated regions were efficiently altered during the sexual process to generate a single copy in the progeny. No progeny were recovered that had undergone RIP (repeat induced point mutation) sufficient to inactivate the mt a-1 gene. We infer that the mt a-1 gene is necessary and sufficient to specify a mating type identity in all vegetative and sexual activities. Mt a-1 may also play an essential role in ascosporogenesis after fertilization.

Cloning, Molecular↗
PubMed1994

The protective properties of liquid perfluorocarbons in phacofragmentation of dislocated lenses.

PURPOSE: In vitro and animal experiments were performed to evaluate the character of retina and pigment epithelium (RPE) damage induced by ultrasonic stream from the tip of a phacofragmentor and to establish the protective properties of perfluorocarbon liquid (PFCL). METHODS: During mechanical vitrectomy in 12 rabbit eyes, the retina were exposed to ultrasound from different distances and with different powers, with and without PFCL. Electron microscopic examination was then performed to assess damage. RESULTS: Ultrasound failed to penetrate the layer of PFCL in vitro. In eyes not injected with PFCL, exposure to the stream from 2 mm and 4 mm at both 50% and 100% powers led to retinal hole formation within 45 to 155 seconds. Damage to the RPE was found in the projection of the hole and within 1 mm from its edge under intact retina. After exposure from 6 mm and in eyes injected with PFCL, the retina and RPE were unchanged. CONCLUSION: It is concluded that the ultrasonic stream from a phacofragmentor may damage the retina sufficiently to cause tears, but that the interface between perfluoro-n-octane and intraocular fluid provides a reflective surface that protects the posterior pole from the stream induced by ultrasound.

Animals↗