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Biomedical subjects

M Chee

Publications and source records attributed to M Chee.

At least 19 recordsLinked to original sources
PubMed2000

Overlap and dissociation of semantic processing of Chinese characters, English words, and pictures: evidence from fMRI.

The functional anatomy of Chinese character processing was investigated using fMRI. Right-handed Mandarin-English bilingual participants made either semantic or perceptual size judgements with characters and pictures. Areas jointly activated by character and picture semantic tasks compared to size judgement tasks included the left prefrontal region (BA 9, 44, 45), left posterior temporal, left fusiform, and left parietal regions. Character processing produced greater activation than picture processing in the left mid and posterior temporal as well as left prefrontal regions. The lateral occipital regions were more active during picture semantic processing than character semantic processing. A similar pattern of activation and contrasts was observed when English words and pictures were compared in another set of bilingual participants. However, there was less contrast between word and picture semantic processing than between character and picture processing in the left prefrontal region. When character and word semantic processing were compared directly in a third group, the loci of activation peaks was similar in both languages but Chinese character semantic processing was associated with a larger MR signal change. The semantic processing of Chinese characters, English words, and pictures activates a common semantic system within which there are modality-specific differences. The semantic processing of Chinese characters more closely resembles English words than pictures.

Adult↗
PubMed1999

A novel method for determining linkage between DNA sequences: hybridization to paired probe arrays.

Cooperative hybridization has been used to establish physical linkage between two loci on a DNA strand. Linkage was detected by hybridization to a new type of high-density oligonucleotide array. Each synthesis location on the array contains a mixture of two different probe sequences. Each of the two probes can hybridize independently to a different target sequence, but if the two target sequences are physically linked there is a cooperative increase in hybridization yield. The ability to create and control non-linear effects raises a host of possibilities for applications of oligonucleotide array hybridization. The method has been used to assign linkage in 50:50 mixtures of DNA containing single nucleotide polymorphisms (SNPs) separated by 17, 693, 1350 and 2038 bp and to reconstruct haplotypes. Other potential uses include increasing the specificity of hybridization in mutation detection and gene expression monitoring applications, determining SNP haplotypes, characterizing repetitive sequences, such as short tandem repeats, and aiding contig assembly in sequen-cing by hybridization.

Genetic Linkage↗
PubMed1998

Large-scale identification, mapping, and genotyping of single-nucleotide polymorphisms in the human genome.

Single-nucleotide polymorphisms (SNPs) are the most frequent type of variation in the human genome, and they provide powerful tools for a variety of medical genetic studies. In a large-scale survey for SNPs, 2.3 megabases of human genomic DNA was examined by a combination of gel-based sequencing and high-density variation-detection DNA chips. A total of 3241 candidate SNPs were identified. A genetic map was constructed showing the location of 2227 of these SNPs. Prototype genotyping chips were developed that allow simultaneous genotyping of 500 SNPs. The results provide a characterization of human diversity at the nucleotide level and demonstrate the feasibility of large-scale identification of human SNPs.

Algorithms↗
PubMed1997

Nucleotide sequence analysis of the human KCNJ1 potassium channel locus.

Detailed analyses of transcripts encoding various isoforms of the human potassium (K+, inward rectifying) channel ROM-K (also referred to as K(ir)1.1) revealed the existence of at least five distinct transcripts [Shuck et al., J. Biol. Chem. 269 (1994) 24261-24270]. These five hROM-K transcripts appear to be the result of alternative splicing of five exons. The nucleotide sequence of the genomic DNA including and spanning these exons (the KCNJ1 locus) was obtained directly from lambda and P1 clones (a total of 40 kb). The organization of the hKCNJ1 gene was determined by combining this sequence information with data obtained from primer extension and RT-PCR experiments. It appears that the hKCNJ1 gene utilizes multiple promoters, with promoter-like elements found 5' of exons 1, 4, or 5. The promoter 5' of exon 5 was unexpected; thus, it appears that the hKCNJ1 gene is capable of producing six distinct hROM-K transcripts via the use of three promoters and alternative splicing of five exons. Comparisons of the rat and human ROM-K cDNA sequences find human homologs (orthologs) for two of the three distinct rROM-K transcripts. A search of the complete human KCNJ1 sequence with the exon sequence that defines the other rROM-K transcript located a region of shared nucleotides, a putative sixth exon, in the hKCNJ1 gene. This finding suggests that the rKCNJ1 gene may contain an exon that is no longer or infrequently used in transcripts derived from the hKCNJ1 gene.

Amino Acid Sequence↗
PubMed1997

Genetic content and preliminary transcriptional analysis of a representative region of murine gammaherpesvirus 68.

Murine gammaherpesvirus 68 (MHV-68) is a relatively recently discovered pathogen of wild rodents and provides a unique opportunity to explore in detail the interactions of a gammaherpesvirus with its natural host. It may also provide a much needed small animal model for human gammaherpesviruses. As a step in the detailed analysis of virus gene structure and expression we have sequenced over 20 kb of the MHV-68 genome and mapped gene transcripts by Northern blot hybridization. The region we chose to analyse contains several conserved gene blocks as well as some less well conserved genes and allowed us to estimate the relationship of this virus to other herpesvirus family members. Of particular interest is the fact that none of the characteristic Epstein-Barr virus (EBV) genes is present at this genomic locus although MHV-68 does have one gene encoding a membrane glycoprotein, 9p150, which shows similarities to the major membrane glycoprotein of EBV. Our results further confirm that MHV-68 is a gammaherpesvirus marginally more closely related to a cluster of gammaherpesviruses including herpesvirus salmiri than to EBV. Northern analysis shows that the temporal regulation of expression is broadly similar to that of other herpesviruses in this region of the genome. We also show that like other gammaherpesviruses, MHV-68 splices its homologue of the EBV transcriptional activator gene BMRF1.

Animals↗
PubMed1996

Accessing genetic information with high-density DNA arrays.

Rapid access to genetic information is central to the revolution taking place in molecular genetics. The simultaneous analysis of the entire human mitochondrial genome is described here. DNA arrays containing up to 135,000 probes complementary to the 16.6-kilobase human mitochondrial genome were generated by light-directed chemical synthesis. A two-color labeling scheme was developed that allows simultaneous comparison of a polymorphic target to a reference DNA or RNA. Complete hybridization patterns were revealed in a matter of minutes. Sequence polymorphisms were detected with single-base resolution and unprecedented efficiency. The methods described are generic and can be used to address a variety of questions in molecular genetics including gene expression, genetic linkage, and genetic variability.

Algorithms↗
PubMed1996

Extensive polymorphisms observed in HIV-1 clade B protease gene using high-density oligonucleotide arrays.

Naturally occurring mutations in HIV-1-infected patients have important implications for therapy and the outcome of clinical studies. However, little is known about the prevalence of mutations that confer resistance to HIV-1 protease inhibitors in isolates derived from patients naive for such inhibitors. In the first clinical application of high-density oligonucleotide array sequencing, the sequences of 167 viral isolates from 102 patients have been determined. The DNA sequence of USA HIV-1 clade B proteases was found to be extremely variable and 47.5% of the 99 amino acid positions varied. This level of amino acid diversity is greater than that previously known for all worldwide HIV-1 clades combined (40%). Many of the amino acid changes that are known to contribute to drug resistance occurred as natural polymorphisms in isolates from patients who had never received protease inhibitors.

Amino Acid Sequence↗
PubMed1995

Using oligonucleotide probe arrays to access genetic diversity.

As the Human Genome Project and related efforts identify and determine the DNA sequences of human genes, it is important that highly reliable and efficient mechanisms are found to access individual genetic variation. It is only through a greater understanding of genetic diversity that the true benefit of the Human Genome Project will be realized. One approach, hybridization to high-density arrays of oligonucleotides, is a fast and effective means of accessing this genetic variation. Light-directed chemical synthesis has been used to generate miniaturized, high-density arrays of oligonucleotide probes. Application-specific oligonucleotide probe array designs have been developed for the rapid screening of characterized genes. Dedicated instrumentation and software have been developed for array hybridization, fluorescence detection and data acquisition and analysis. In a specific and challenging application, oligonucleotide probe arrays have been used to screen the reverse transcriptase and protease genes of the highly polymorphic HIV-1 genome to explore genetic diversity and detect mutations conferring resistance to antiviral drugs. Results from this application strongly suggest that oligonucleotide probe arrays will be a powerful tool for rapid investigations in sequence checking, pathogen detection, expression monitoring and DNA molecular recognition.

Base Sequence↗
PubMed1993

Epilepsy surgery in children and adults.

Epilepsy surgery is now accepted as a treatment modality for medically intractable epilepsy. A careful and detailed evaluation of patients is required by a trained epilepsy team which includes neurosurgeons, neurologists, neuroradiologists, psychologists and psychiatrists. For intractable complex partial seizures of temporal lobe origin, epilepsy surgery offers an 80% success rate.

Adult↗
PubMed1991

Enzymatic multiplex DNA sequencing.

The problem of reading DNA sequence films has been reformulated using an easily implemented, multiplex version of enzymatic DNA sequencing. By utilizing a uniquely tagged primer for each base-specific sequencing reaction, the four reactions can be pooled and electrophoresed in a single lane. This approach has been previously proposed for use with fluorescently labelled probes (1), and is analogous to the principle used in four-dye fluorescence sequencing except that the signals are resolved following electrophoresis (2). After transfer to a nylon membrane, images are obtained separately for each of the four reactions by hybridization using oligonucleotide probes. The images can then be superimposed to reconstitute a complete sequence pattern. In this way the correction of gel distortion effects and accurate band registration are considerably simplified, as each of the four base-specific ladders require very similar corrections. The methods therefore provide the basis for a second generation of more accurate and reliable film reading programs, as well as being useful for conventional multiplex sequencing. Unlike the original multiplex protocol (3), the approach described is suitable for small projects, as multiple cloning vectors are not used. Although more than one vector can be utilized, only a library of fragments cloned into any single phage, phagemid or plasmid vector is actually required, together with a set of tagged oligonucleotide primers.

Base Sequence↗
PubMed1990

Herpesviruses: a study of parts.

Dormancy, an adaptation to survival in a hostile environment, is a trait common to herpesviruses. Two other features are a large (0.1-0.25 Mb) and mutile (inherently easily mutable) genome. The complete nucleotide sequences of four herpesviruses have recently been determined. This database is unparalleled in allowing the comparative evolutionary study of a complex group of viruses in eukaryotes. In this article, we examine aspects of herpesvirus diversity in the light of recent studies which have revealed characteristics that unify the family at the genetic level.

DNA Replication↗
PubMed1990

Human herpesvirus 6 is closely related to human cytomegalovirus.

A sequence of 21,858 base pairs from the genome of human herpesvirus 6 (HHV-6) strain U1102 is presented. The sequence has a mean composition of 41% G + C, and the observed frequency of CpG dinucleotides is close to that predicted from this mononucleotide composition. The sequence contains 17 complete open reading frames (ORFs) and part of another at the 5' end of the sequence. The predicted protein products of two of these ORFs have no recognizable homologs in the genomes of other sequenced human herpesviruses (i.e., Epstein-Barr virus [EBV], human cytomegalovirus [HCMV], herpes simplex virus [HSV], and varicella-zoster virus [VZV]). However, the products of nine other ORFs are clearly homologous to a set of genes that is conserved in all other sequenced herpesviruses, including homologs of the alkaline exonuclease, the phosphotransferase, the spliced ORF, and the major capsid protein genes. Measurements of similarity between these homologous sequences showed that HHV-6 is clearly most closely related to HCMV. The degree of relatedness between HHV-6 and HCMV was commensurate with that observed in comparisons between HSV and VZV or EBV and herpesvirus saimiri and significantly greater than its relatedness to EBV, HSV, or VZV. In addition, the gene for the major capsid protein and its 5' neighbor are reoriented with respect to the spliced ORFs in the genomes of both HHV-6 and HCMV relative to the organization observed in EBV, HSV, and VZV. Three ORFs in HHV-6 have recognizable homologs only in the genome of HCMV. Despite differences in gross composition and size, we conclude that the genomes of HHV-6 and HCMV are closely related.

Amino Acid Sequence↗
PubMed1990

Focal seizure in non-ketotic hyperglycaemia.

Structural brain lesions are the common causes of focal seizure. We report two patients who presented with focal fits with non-ketotic hyperglycaemia. There were no focal brain lesions to account for the fits. The fit of one patient was aborted by intravenous phenytoin while the other by controlling the blood sugar.

Aged↗
PubMed1989

Identification of the major capsid protein gene of human cytomegalovirus.

The coding region for the major capsid protein (MCP) of human cytomegalovirus (HCMV) was identified by comparing the protein sequence with the respective sequences of herpes simplex virus (HSV), Epstein-Barr virus, and varicella-zoster virus. The predicted length of the HCMV MCP was 1,370 amino acids. Comparison of the MCP sequences of the different human herpesviruses showed a homology of 25% to the MCP of HSV type 1, a homology of 29% to the MCP of Epstein-Barr virus, and a homology of 23% to the MCP of varicella-zoster virus. A subfragment of the HSV type 1 KpnI i fragment encoding the MCP VP5 cross-hybridized with the HCMV HindIII U fragment containing part of the MCP gene. Northern (RNA) blot analyses with subclones out of the coding region for the HCMV MCP detected one large transcript of about 8 kilobases. A portion of the open reading frame was expressed in Escherichia coli plasmid pBD2 IC2OH as a beta-galactosidase fusion protein and was used to generate polyclonal antibodies in New Zealand White rabbits. The obtained antisera reacted in Western immunoblots with the MCP of purified HCMV virions. A monoclonal antibody against the human MCP and a monospecific rabbit antiserum against strain Colburn of simian cytomegalovirus detected the fusion protein as well as the MCP of purified virions in immunoblots.

Amino Acid Sequence↗
PubMed1980

Hypothermic pulsatile perfusion: its use in the preservation of pancreases for 24 to 48 hours before islet cell transplantation.

Canine pancreases underwent hypothermic pulsatile perfusion for 24 or 48 hours before islet cell collagenase digestion and intrasplenic autotransplantation. The numbers of dogs surviving longer than two months are as follows: dogs receiving pancreatectomies, 0/10; dogs receiving 24-hour-perfused islet cells, 6/10, dogs receiving 48-hour-perfused islet cells, 4/10; and dogs receiving fresh islet cells, 7/10. Islet cells from 48-hour-perfused pancreases were not as good in reversing hyperglycemia as the islet cells from 24-hour-perfused pancreases. Histologically, the islet cells appeared to be normal in the fresh and 24-hour-perfused pancreases. Thus, hypothermic pulsatile perfusion of pancreas autografts for 24 hours appears to be a safe and reliable method. When this technique is used clinically, special attention should be given to 48-hour-perfused pancreases because the reversal of hyperglycemia sometime is not complete.

Amylases↗
PubMed1980

Lung transplantation: better survival results after graft pretreatment with concanavalin A or chondroitin sulfate.

Pretreatment of the lung graft with concanavalin A (Con A) or chondroitin sulfate (CIS) was used to modify the lung allograft response after transplantation into moderately immunosuppressed (low doses of azathioprine and prednisone) recipients. Significant (p less than 0.05) prolongation of survival was observed after graft pretreatment. Pneumonia and rejection were the most frequent causes of death for all groups of dogs. However, only 3 out of 6 animals from each of the groups with pretreated grafts died of pneumonia or rejection, whereas 5 of the 6 animals in the control group died of these causes. Furthermore, when rejection occurred in the dogs with lung grafts pretreated with Con A or CIS, it was considerably delayed compared with the controls. Partial pressure of arterial oxygen, chest roentgenograms, and lung histology were good indicators of lung viability after transplantation.

Animals↗