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Biomedical subjects

M J Chen

Publications and source records attributed to M J Chen.

At least 127 records · Page 7Linked to original sources
PubMed1985

Adult T-cell leukemia/lymphoma in Taiwan. A clinicopathologic observation.

The retrovirus-associated adult T-cell leukemia/lymphoma (ATL) has not been previously documented in Taiwan. Five cases identified recently by the authors are reported. Three of the patients were women, and their ages ranged from 36 to 60 years. The most important diagnostic clue was the observation of polylobated lymphoid cells in the peripheral blood. Other variably observed significant features included hypercalcemia, cutaneous eruptions, osteolytic bone lesion, hepatomegaly, and lymphadenopathy. Surface marker studies revealed that the leukemic or lymphoma cells were T-helper cells. Histopathologic examination revealed one case of pleomorphic type and three cases of medium-sized cell type. No tissue was available for study in one case. The diagnosis of ATL was confirmed by the indirect immunofluorescence test on MT-1 cell for antibodies to adult T-cell leukemia virus-associated antigen (ATLA). Three patients were dead within 6 months, and two patients had been in clinical remission for 7 and 10 months, respectively. These two latter cases were similar to the so-called smoldering type of ATL. Two descendents among nine relatives of the patients were also positive for anti-ATLA (22%). Two husbands were negative. Four of the five patients lived in the same county in northeastern coastal Taiwan, which suggested a possible clustering of ATL in that region.

Adult↗
PubMed1985

Serological survey of antibodies to the adult T-cell leukemia virus-associated antigen (HTLV-A) in Taiwan.

A serological survey of antibodies to the adult T-cell leukemia virus-associated antigen (HTLV-A) conducted in Taiwan revealed II seropositive individuals among 2,565 serum donors tested, which included 1,187 hospital or free clinic patients, 1,065 blood donors and 313 aborigines. The overall prevalence rate was 0.43% and was 0.90% (9/995) for adults aged 40 years or over, which was similar to the rates observed in the non-endemic areas in Japan. No highly prevalent area was demonstrated. The II seropositive individuals identified were 8 hospital or clinic patients, 1 blood donor and 2 aborigines. Among 108 various leukemia/lymphoma patients also studied, 7 were positive. These 7 anti-HTLV-A-positive patients also had clinicopathologic features of adult T-cell leukemia/lymphoma (ATL). Among 21 relatives of 3 seropositive individuals in the epidemiologic study, 2 were positive; and among 25 relatives of 5 ATL patients, 6 were positive. Our data support the contention that horizontal familial transmission of human T-cell leukemia virus (HTLV-I) is an important route and HTLV-I infection can occur on a different genetic background. Furthermore, the antibody titer did not correlate with the manifestation or the state of the disease.

Adolescent↗
PubMed1985

Cutaneous manifestations of adult T cell leukemia/lymphoma. Report of three different forms.

The clinical and pathologic features of cutaneous lesions observed in three adult T cell leukemia/lymphoma (ATL) patients identified in Taiwan are described. They represent one classical case of ATL and two "smoldering" variants. The classical ATL patient when first seen had numerous erythematous or purpuric papules, nodules, and plaques with or without ulceration. The two "smoldering" cases developed encrusted purpuric plaques with subcutaneous erythematous nodules in one patient and pompholyx-like vesicular eruptions with tumor masses in another patient. The pompholyx-like eruptions have not been described before. Pruritus was the major complaint in two patients. Histopathologic studies revealed pleomorphic infiltration in the classical case and monomorphic infiltration with medium-sized cells in the two "smoldering" variants. Therefore, the cutaneous lesions of ATL are diverse and not pathognomonic. The diagnosis requires a high index of suspicion, detection of circulating characteristic multilobated lymphoid cells with T helper/inducer cell marker, and demonstration of serum antibody against the adult T cell leukemia virus-associated antigen.

Adult↗
PubMed1984

The functional human dihydrofolate reductase gene.

Molecular cloning, mapping, and DNA sequencing techniques have been used to characterize the functional human dihydrofolate reductase (DHFR) gene. The gene is about 30 kilobases in length. Its coding portions are separated into 6 exons, the intron-exon boundaries of which are identical to those of the previously characterized mouse DHFR gene. The 5 introns vary in length from 362 to 12,000 base pairs. The position of the DHFR gene promoter was identified as being shortly upstream from the initiation codon in an in vitro transcription reaction by polymerase II. A DHFR minigene was constructed in a plasmid expression vector by combining a DNA fragment containing exon 1, intron I, and a small part of exon 2 from the functional gene, with a second DNA fragment containing exons 2-6 from a processed intronless gene, the coding sequences of which are identical to those of the normal locus. Transcription initiation from the DHFR promoter was localized to a position 71 +/- 2 base pairs upstream from the initiation codon, both in monkey kidney cells transfected with vectors containing the DHFR minigene, and in human HeLa cells. This single transcription start and the three previously identified polyadenylation sites account for the 800-, 1,000-, and 3,800-nucleotide DHFR mRNA species found in human cells. On comparison of the mouse and human DHFR genes, sequence homology was shown to be limited to the coding regions and 100 base pairs of the 3' untranslated region up to the first polyadenylation site of both genes. In addition, there is fairly extensive homology in the 5' flanking region, although the quadruply repeated 48-base pair sequence found in the mouse genome is represented only once in human DNA.

Base Sequence↗
PubMed1984

A human dihydrofolate reductase intronless pseudogene with an Alu repetitive sequence: multiple DNA insertions at a single chromosomal site.

A dihydrofolate reductase (DHFR) pseudogene, hDHFR-psi 3 has been isolated from a human genomic DNA fragment library. Sequence analysis of this gene revealed a lack of introns and the presence of a tract of nine adenines, 90 bp downstream from the end of the coding sequence. These features suggest that hDHFR-psi 3 was derived from a processed RNA molecule that has been converted into DNA and inserted into a chromosome, analogous to the origin of three intronless human DHFR genes previously described. An interesting feature of hDHFR-psi 3 is the presence of a member of the Alu moderately repetitive DNA sequence family within the DHFR coding region. This Alu element is flanked by a 16 bp directly repeated DNA segment derived from DHFR coding sequences. The Alu element apparently has been inserted into the intronless DHFR pseudogene and thus, there have been two insertions at a single chromosomal locus. The hDHFR-psi 3 contains only the 3' half of the DHFR coding sequence. Immediately upstream from the directly repeated sequence before the Alu element is an adenine-rich tract. The DNA farther upstream is moderately repetitive and is related to neither DHFR nor Alu DNA sequence. Therefore, it seems possible that a third insertion has occurred at the same site further disrupting the hDHFR coding sequences.

Base Sequence↗
PubMed1984

Representational drawings of solid objects by young children.

Two groups of children aged 6 and 8 years were given three tasks requiring graphical representations of solid geometric forms. These tasks were drawing from life models, copying from photographs, and copying from line drawings of these objects. Performance was assessed on the basis of level of approximation to correct perspective. Older children used more perspective features than younger children in their drawings. At all ages, the drawings from life were most difficult. Results on the two copying tasks were not consistent. Drawings made by copying photographs were either as advanced as or poorer than copies of line drawings. The results are explained in terms of the difficulties exhibited by young children in translating the three-dimensional scene to a two-dimensional picture plane and strategies adopted by them to cope with these problems.

Art↗
PubMed1984

Chromosomal organization of the human dihydrofolate reductase genes: dispersion, selective amplification, and a novel form of polymorphism.

The human dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate: NADP+ oxidoreductase, EC 1.5.1.3) gene family includes a functional gene (hDHFR) and at least four intronless genes. Three intronless genes (hDHFR-psi 2, hDHFR-psi 3, and hDHFR-psi 4) are identifiable as pseudogenes because of DNA sequence divergence from the functional gene with introns, while one intronless gene (hDHFR-psi 1) is completely homologous to the coding sequences of the functional gene. Analysis of genomic DNA from two panels of somatic human-rodent cell hybrids with specific molecular probes provide insight into the chromosomal organization and assignment of these genes. The five genes are dispersed in that each one is found on a different chromosome. The functional gene hDHFR has been assigned to chromosome 5, and one pseudogene (hDHFR-psi 4), to chromosome 3. In a human cell line (HeLa) that was selected for methotrexate resistance, the functional locus became amplified, while there was no amplification of the four intronless pseudogenes. hDHFR-psi 1 was found to be present in DNA of some individuals and absent from DNA of others, consistent with a recent evolutionary origin of this gene originally suggested by its sequence identity to the coding portions of the functional gene. The presence or absence of this intronless pseudogene represents a previously unreported form of DNA polymorphism.

Animals↗
PubMed1983

Timing of dispersal in juvenile jewel fish during development is unaffected by available space.

The spatial distributions of 2 groups of sibling juvenile jewel fish were examined between 58 and 99 days of age to determine the effects of spatial experience on the timing of dispersal from a more aggregative behavioral mode. One group was provided a seminatural 1000-liter aquarium, the other with 70% less space per fish, but both groups were able to observe the same number of fish. Using a computer and digitizing tablet, distances between 1st-6th nearest neighbors were measured from time-sampled video recordings of spatial distributions in either overhead or underneath plan views. Both groups exhibited changes in aggregative behavior that were remarkably similar. Between 65 and 92 days of age, both groups showed gradual dispersal, which accelerated abruptly at 93-99 days of age. These results suggest that the timing of dispersal is regulated by developmental processes operating independently of spatial experience.

Animals↗
PubMed1982

Intronless human dihydrofolate reductase genes are derived from processed RNA molecules.

Three groups of recombinant bacteriophage containing coding sequences for dihydrofolate reductase (DHFR; tetrahydrofolate dehydrogenase; 5,6,7,8-tetrahydrofolate:NADP+ oxidoreductase, EC 1.5.1.3) were isolated from two human DNA clone libraries. One recombinant (lambda hDHFR-1) contains three exons that encode the COOH-terminal portion of human DHFR. The other two human DHFR genes (hDHFR-psi 1 and hDHRF-psi 2) lack introns. hDHFR-psi 2 contains several in-phase termination codons and is only 93% homologous to the normal human DHFR coding sequences, whereas hDHFR-psi 1 has an open reading frame and is virtually identical to the coding sequence of the normal DHFR gene. The region of DNA sequence homology between each intronless gene and the normal DHFR gene extends 2.9 kilobases beyond the end of the coding sequences. At the 3' end of this homologous sequence, each intronless gene has an A-rich tract. The lack of introns and the presence of the 3' A-rich tract suggest that hDHFR-psi 1 and hDHFR-psi 2 were derived from processed RNA molecules. A short DNA sequence, 60 nucleotides 5' to the ATG start codon in lambda hDHFR-psi 2, is directly repeated immediately after the 3' A-rich tract; such terminal direct repeats also flank integrated proretroviruses and transposable DNA elements and are thought to be the hallmark of inserted DNA sequences.

Base Sequence↗
PubMed1981

Structure and expression of human globin genes introduced into mouse fibroblasts.

The human delta- and beta-globin genes, contained in a recombinant bacteriophage (lambda H beta G1), were introduced into mouse fibroblasts by cotransformation with a plasmid (chi 1) containing the herpes simplex thymidine kinase gene using the calcium phosphate precipitation technique. A molar ratio of lambda H eta G1 to chi 1 DNA of 3:1 was used. Four of the eleven stable transformants obtained contained intact delta- and beta-globin genes as determined by Southern blot analysis. To assess methylation in the segment of human DNA introduced into mouse cells, digestion with Hpa II or Msp I alone or with a second restriction enzyme was performed. The sites examined near the human delta- and beta-globin genes in transformed cells were not methylated. RNA extracted from the transformed cells was analyzed by RNA-cDNA hybridization; no more than 100 copies of human beta-globin mRNA/cell were found. Although hypomethylation of sites surrounding expressed globin genes in erythroid cells has been described, this property is not sufficient to ensure a high level of expression in fibroblasts.

Animals↗
PubMed1980

Hemoglobin switching in sheep. Cloning and characterization of the beta A and beta-like embryonic globin genes from genomic DNA.

Genomic DNA from a fetal sheep homozygous for the beta A gene was used to construct a library of one million cloned DNA fragments using the bacteriophage vector, Charon 4A. Screening of 150,000 plaques from this library using radioactive beta-globin gene sequences resulted in the isolation of two recombinant bacteriophage containing globin genes. One of these, S beta AG-21, contains the complete adult beta A-globin gene as demonstrated by hybridization and restriction endonuclease analysis. In common with adult globin genes from other species, the beta A gene contains small (105 base pairs) and large (900 base pairs) intervening sequences. The second recombinant bacteriophage, SG-4, contains a complete embryonic beta-like globin gene which is expressed in the sheep embryo as demonstrated by hybridization analysis with cDNA made from sheep embryonic globin mRNA. Although differing in its restriction endonuclease map from the adult beta-globin genes, SG-4 appears to contain a large intervening sequence of at least 750 base pairs in length. Finally, preliminary evidence is discussed which indicates that a Pvu II site just 5' to the Cap site may be a common feature of sheep globin genes.

Animals↗
PubMed1977

Abstraction of information from a complex display.

Two experiments concerned with simultaneously abstracting information about different dimensions from the same display were carried out. In experiment 1 the subject was briefly shown a complex display containing coloured forms with three values of each dimension. Instead of identifying the individual items in the display (such as red triangle, blue square, etc), the subject was to abstract and report in any order the different dimensional values (e.g. red and blue for colour, and triangle and square for form). The results showed that the accuracy of performance was independent of the way in which two dimensions were combined, whether they were orthogonal, partially correlated, or completely correlated. The results showed that colour and form were processed independently and that the perception of one was not facilitated or interfered with by the presence of the other in the same display. In experiment 2 various numbers of values from each dimension were combined orthogonally within each display. The subject's task was the same as in the previous experiment except that the order of report of the two dimensions was specified for each subject. Suppose the dimension reported first is X, and that reported second is Y. The results showed that the number of X values not only detrimentally affected the accuracy of reporting the X values, it also reduced the accuracy of reporting Y owing to memory impairment. The number of Y values, on the other hand, affected only the report of Y values. The results were discussed in terms of a parallel-processing system which proposes no capacity limitation.

Color Perception↗
PubMed1976

The physical mapping of bacteriophage T5 transfer tRNAs.

Transfer RNAs, isolated from Escherichia coli F cells infected with T5 bacteriophage, were charged with radioactive amino acids and used in RNA-DNA hybridization studies to detect and locate T5 tRNA cistrons in the T5 DNA chromosome. Hybridization of 14 3H-aminoacyl-tRNA species, including purified T5 [35S]Met-tRNAm and [35S]Met-tRNAf, to the separated strands of T5+ DNA indicates that most, if not all, of the T5 tRNAs are transcribed from the continuous heavy strand of T5 DNA. Heteroduplex mapping of eight mutant T5 DNA deletions has enabled us to locate and determine the size of these deleted segments. By correlating this information with the presence and absence of specific tDNA sequences in these mutants, as determined by tRNA-DNA hybridization, we were able to define the physical limits of four tDNA-containing loci along the T5 DNA molecule. A physical map for 15 tRNA species examined indicates that the structural genes for these tRNAs are clustered within a segment length of T5 DNA that represents approximately 11.2% of the total wild type T5 DNA. The existence of the deletion mutants indicates that T5 tRNAs are dispensable for T5 replication under the growth conditions and for the host employed.

Amino Acids↗
PubMed1975

Methionine and formylmethionine specific tRNAs coded by bacteriophage T5.

By RNA-DNA hybridization, as well as chemical and chromatographic analysis, evidence is provided that the bacteriophage T5 codes for the synthesis of two isoacceptor methionine transfer RNA species, tRNA-Met and tRNA-f-Met. Because of the differences in chromatographic properties of T5 phage and host methionine tRNAs, the phage tRNA species are readily distinguishable.

Chromatography↗