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Biomedical subjects

F C Leung

Publications and source records attributed to F C Leung.

At least 19 recordsLinked to original sources
PubMed2006

Cloning and characterization of chicken growth hormone binding protein (cGHBP).

Growth hormone (GH) is indispensable for the growth of animals and its biological activity is mediated by binding to the growth hormone receptor (GHR) [Harvey S, Scanes CG, Daughaday WH. Growth hormone. Boca Raton: CRC Press; 1995]. GHR is a transmembrane protein responsible for signal transduction upon GH binding. GH also binds to the growth hormone binding protein (GHBP) which is the soluble form of GHR extracellular domain existing in circulation. Actions of GHBP include prolongation of GH bioavailability and prevention of GH signaling system from over-stimulation. To date, little is known about the mechanisms generating the chicken GHBP (cGHBP). Elucidating the genomic structure of cGHR will provide insights into such underlying mechanisms. Using polymerase chain reaction and library screening methods, we have characterized the genomic organization of chicken GHR (cGHR). The full-length coding region of the cGHR transcript is composed of eight exons (exons 2-10), lacking a human homolog exon 3 and spans at least 71 kb on the genome. A novel transcript of size 1.2kb was isolated from chicken liver total RNA using 5' and 3' rapid cDNA ends amplification (RACE). It was generated by utilizing a previously unknown polyadenylation signal located at the intron 6. Semi-quantitative reverse transcription polymerase chain reaction showed that this transcript is widely expressed in a variety of tissues. This transcript has an open reading frame comprising 203 amino acids. In vitro binding assay using ELISA demonstrated that Escherichia coli expressed recombinant protein encoded by this transcript was able to bind with chicken GH. Hence, this transcript is a potential candidate for cGHBP.

Amino Acid Sequence↗
PubMed2006

Expression profiles of growth hormone-releasing hormone and growth hormone-releasing hormone receptor during chicken embryonic pituitary development.

Growth hormone-releasing hormone (GHRH) and its receptor (GHRHR) have long been regarded as the critical molecules for the stimulation of growth hormone (GH) synthesis and release, as well as the regulation of pituitary somatotroph expansion in vertebrates. However, little is known about their expression in the embryonic pituitaries of birds. In this study, the full-length cDNA for chicken GHRHR was cloned from the chicken pituitary. It encodes 419 amino acids and shares high homology with that of the human, rat, and mouse. As in those in mammals, chicken GHRHR is predominantly expressed in the pituitary and weakly expressed in several extra-pituitary tissues including brain, pancreas, testis, and kidney, among 12 tissues examined. Using semiquantitative reverse transcription-PCR, we further examined the expression of GH, GHRH, and GHRHR during embryonic pituitary development. The expression of GHRHR on embryonic d 8 was much lower, but abundant expression was noticed as early as embryonic d 12. In contrast, the level of pituitary GHRH mRNA peaked on d 8 and declined sharply afterwards. Interestingly, unlike those of pituitary GHRH and GHRHR, the higher expression levels of GH appeared much later (from d 16 to 20). The differential expressions of GHRH, GHRHR, and GH in the developing embryonic pituitaries not only imply that pituitary-derived GHRH (or pituitary adenylate cyclase-activating polypeptide) and GHRHR may have a paracrine/autocrine role in the expansion of undifferentiated somatotroph precursor cells, but also suggest that GHRHR is likely to be involved in the somatotroph differentiation occurring at the later developmental stages.

Amino Acid Sequence↗
PubMed2004

Molecular epidemiology of the novel coronavirus that causes severe acute respiratory syndrome.

BACKGROUND: Severe acute respiratory syndrome (SARS) is a newly emerged disease caused by a novel coronavirus (SARS-CoV), which spread globally in early 2003, affecting over 30 countries. We have used molecular epidemiology to define the patterns of spread of the virus in Hong Kong and beyond. METHODS: The case definition of SARS was based on that recommended by WHO. We genetically sequenced the gene for the S1 unit of the viral spike protein of viruses from patients with SARS in Hong Kong (138) and Guangdong (three) in February to April, 2003. We undertook phylogenetic comparisons with 27 other sequences available from public databases (Genbank). FINDINGS: Most of the Hong Kong viruses (139/142), including those from a large outbreak in an apartment block, clustered closely together with the isolate from a single index case (HKU-33) who came from Guangdong to Hong Kong in late February. Three other isolates were genetically distinct from HKU-33 in Hong Kong during February, but none of these contributed substantially to the subsequent local outbreak. Viruses identified in Guangdong and Beijing were genetically more diverse. INTERPRETATION: The molecular epidemiological evidence suggests that most SARS-CoV from the outbreak in Hong Kong, as well as the viruses from Canada, Vietnam, and Singapore, are genetically closely linked. Three viruses found in Hong Kong in February were phylogenetically distinct from the major cluster, which suggests that several introductions of the virus had occurred, but that only one was associated with the subsequent outbreak in Hong Kong, which in turn spread globally.

Canada↗
PubMed2003

The complete genome sequence of severe acute respiratory syndrome coronavirus strain HKU-39849 (HK-39).

The complete genomic nucleotide sequence (29.7kb) of a Hong Kong severe acute respiratory syndrome (SARS) coronavirus (SARS-CoV) strain HK-39 is determined. Phylogenetic analysis of the genomic sequence reveals it to be a distinct member of the Coronaviridae family. 5' RACE assay confirms the presence of at least six subgenomic transcripts all containing the predicted intergenic sequences. Five open reading frames (ORFs), namely ORF1a, 1b, S, M, and N, are found to be homologues to other CoV members, and three more unknown ORFs (X1, X2, and X3) are unparalleled in all other known CoV species. Optimal alignment and computer analysis of the homologous ORFs has predicted the characteristic structural and functional domains on the putative genes. The overall nucleotides conservation of the homologous ORFs is low (<5%) compared with other known CoVs, implying that HK-39 is a newly emergent SARS-CoV phylogenetically distant from other known members. SimPlot analysis supports this finding, and also suggests that this novel virus is not a product of a recent recombinant from any of the known characterized CoVs. Together, these results confirm that HK-39 is a novel and distinct member of the Coronaviridae family, with unknown origin. The completion of the genomic sequence of the virus will assist in tracing its origin.

3' Untranslated Regions↗
PubMed2002

Genetic diversity of Chinese native chicken breeds based on protein polymorphism, randomly amplified polymorphic DNA, and microsatellite polymorphism.

Genetic diversity of Chinese native chicken breeds was investigated using protein polymorphism, randomly amplified polymorphic DNA (RAPD), and microsatellite polymorphism. Imported broiler and layer breeds were also included in the analysis. The results from protein polymorphism did not show distinct differences between Chinese native chicken and imported broilers; however, there were small significant differences between these two types of chickens. The results from RAPD indicated that gene diversity within a population was large in Chinese native chickens, intermediate in broilers, and low in layers and that there were small differences between Chinese native chickens and both broilers and layers. A great difference between broilers and layers was observed. Microsatellite polymorphism data showed that genetic diversity was high in the Chinese native chickens and low in layers and that there was a close relationship between Chinese native chickens and broiler but a remote relationship between Chinese native chickens and layers. The wide genetic diversity of Chinese native breeds can meet different requirements of breeding for chicken quality in China.

Alkaline Phosphatase↗
PubMed2002

Comparative analysis of allozyme, random amplified polymorphic DNA, and microsatellite polymorphism on Chinese native chickens.

Allozyme, random amplified polymorphic DNA (RAPD), and microsatellite polymorphisms were examined and compared among five native populations of Chinese chickens, two fast-growing broiler lines, and one layer line. Three assay systems resulted in a different average heterozygosity or gene diversity in each of the eight populations. The lowest average heterozygosity was obtained with allozyme analysis (0.2209), intermediate heterozygosity was obtained with RAPD (0.2632), and the highest heterozygosity was observed with microsatellite analysis (0.7591). The genetic distances among all populations measured by three methods were also different. Allozyme data showed close relationships between Chinese native chickens and the two broiler lines, but they were both remotely related to the layer line. Microsatellite polymorphism analysis was similar to the allozyme analysis but genetic distances from RAPD showed a close relationship between Chinese native chickens and broiler and layer chickens.

Albumins↗
PubMed2001

Isolation and characterization of repetitive DNA sequences from Panax ginseng.

Repetitive sequences constitute a significant component of most eukaryotic genomes, and the isolation and characterization of repetitive DNA sequences provide an insight into the organization and evolution of the genome of interest. We report the isolation and characterization of the major classes of repetitive sequences from the genome of Panax ginseng. The isolation of repetitive DNA from P. ginseng was achieved by the reannealing of chemically hydrolyzed (200 bp-1 kb fragments) and heat-denatured genomic DNA to low C(o)t value. The low C(o)t fraction was cloned, and fifty-five P. ginseng clones were identified that contained repetitive sequences. Sequence analysis revealed that the fraction includes repetitive telomeric sequences, species-specific satellite sequences, chloroplast DNA fragments and sequences that are homologous to retrotransposons. Two of the retrotransposon-like sequences are homologous to Ty1/ copia-type retroelements of Zea mays, and six cloned sequences are homologous to various regions of the del retrotransposon of Lilium henryi. The del retrotransposon-like sequences and several novel repetitive DNA sequences from P. ginseng were used to differentiate P. ginseng from P. quinquefolius, and should be useful for evolutionary studies of these disjunct species.

Cloning, Molecular↗
PubMed2001

Genomic growth hormone gene polymorphisms in native Chinese chickens.

Chicken growth hormone (cGH), a polypeptide hormone synthesized in and secreted by the pituitary gland, is involved in a wide variety of physiological functions such as growth, body composition, egg production, aging, and reproduction. Chicken growth hormone polymorphisms have been reported to be associated with certain phenotypes. Our objective is to investigate the GH gene polymorphism in selected strains of native Chinese chickens. Yellow Wai Chow GH gene was characterized by sequencing and was found to have one silent substitution, 31 insertions, and other substitutions spread among the introns. In addition, a novel Mspl site has been identified and characterized in the first intron. Allele frequencies of the intron 1 polymorphism were characterized among 28 populations of native Chinese chickens. Thus, polymorphism of the cGH gene may be useful in phylogenetic analysis, as well as in the design of breeding programs.

Alleles↗
PubMed1999

New applications of low-C0tDNA as a DNA fingerprint probe.

New applications of low-C0t DNA are reported as probes for genetic identification and genome characterization. These fast and intermediately reannealing fractions have sometimes either been discarded in genomic library construction to enhance the probability of finding single copy genes, or they are used as resources for identifying individual repetitive sequences. In addition, they are used as blockers to enhance hybridization signals. C0t-1 DNA serves as a probe for DNA fingerprinting of human yeast artificial chromosomes. We have isolated low-C0t DNA from bacteria, fungus, plant, mussel, chicken, rat and fish from the sheared genomic DNA of the respective species. Low-C0t DNA is labeled to generate DNA fingerprints and for in situ hybridization. Individual specific DNA fingerprint profiles are observed and species-specific DNA fragments can be identified in bacteria, fungus, plants (Ginseng and Amaranthus) and mussel. When low-C0t DNA probes from rat, chicken and fish were employed, only smear profiles and no distinct DNA banding patterns were evident. In these species, individual clones can be used as a probe for DNA fingerprinting containing repetitive sequences after subcloning. The advantage of this approach is to quickly develop a useful probe for DNA fingerprinting for genetic identification and analysis without sequencing knowledge a priori. This represents an innovative approach to the use of these repetitive components of the genome.

Animals↗
PubMed1997

Visual Genome Explorer: a comparative visual interface to genome data.

In response to the deluge of genome data, we are developing Visual Genome Explorer, an interactive graphical interface to genome data. Given is a description of the prototype program, which introduces the concept of visual comparative genomics for complete bacterial genomes.

Computer Communication Networks↗
PubMed1997

[DNA polymorphism in the genomes of different Escherichia coli strains].

Bacteria have been traditionally classified on the basis of their morphology, biochemical reaction, serology and etc. However, in some case these methods could not authenticate the closely related bacteria strains. In this study, we cloned two repetitive DNA sequences with 0.9 and 0.6 kb in length from Escherichia coli K12 strain JM109 and designated as ECR-1 and ECR-6 respectively. Using ECR-1 and ECR-6 sequences or their combination as the probes for DNA polymorphism analysis, we were be able to develop a molecular method of biotyping for the identification of very closely related strains of Escherichia coli. Both of ECR-1 and ECR-6 probes could be applied for the taxonomy, epidemiological and microecological studies, and clinical diagnosis for pathogenic Escherichia coli strains.

DNA, Bacterial↗
PubMed1996

Hypothyroidism alters the effect of GTP on adenylyl cyclase in forebrain and hindbrain synaptosomal membranes from 15-day-old rats.

The effect of GTP concentration of forskolin-stimulated adenylyl cyclase activity was examined in synaptosomal membranes from 15-day-old rats that were hypothyroid owing to administration of propylthiouracil and a low-iodine diet to the mothers during pregnancy and suckling. In membranes from the forebrain hypothyroidism abolished the overall stimulatory effect of GTP, which was seen in the euthyroid case. In membranes from the hindbrain hypothyroidism had the opposite effect in that there was an enhancement of an overall stimulatory effect of GTP. It is suggested that these findings reflect changes during early development of the brain in the expression of various G-proteins and/or the expression of different isoforms of adenylyl cyclase.

Adenylyl Cyclases↗
PubMed1996

Signal transduction processes in the developing brain: perturbations of G protein alpha-subunit abundances by perinatal hypothyroidism.

The abundances of G protein alpha-subunits (Gi1 alpha, Gi2 alpha, G0 alpha and Gq/ll alpha) were measured in synaptosomal membranes isolated from forebrain and hindbrain regions of euthyroid and hypothyroid neonatal rats at 10, 15, 20 and 25 days post-partum. The findings show that hypothyroidism causes a distinct perturbation of the normal developmental profile of these signalling components. It is suggested that these changes may contribute to some of the neurological deficits arising from hypothyroidism in early development.

Animals↗
PubMed1993

A computer program to aid in calculating similarity indexes from DNA fingerprints.

DNA SIMDEX is a DOS-based computer program designed to assist in the visual scoring of DNA fingerprint assays. DNA SIMDEX uses the migration distances of the individual DNA bands to generate lists of probable matching and nonmatching bands and automatically calculates a probable similarity index between DNA fingerprints based on these initial predictions. After comparisons are edited by the user, the final similarity index, along with accompanying data, can be saved on a floppy disk or hard drive for easy storage and retrieval or can be printed directly on a laser or line printer. The program has been developed to function with or without an image-analysis system, thus making it an inexpensive alternative for small laboratories.

DNA Fingerprinting↗
PubMed1992

Treatment with triiodothyronine decreases the abundance of the alpha-subunits of Gi1 and Gi2 in the cerebral cortex.

Treatment of rats for 3 days with T3 halved the abundance of the alpha-subunits of Gi1 and Gi2 in synaptosomal membranes isolated from the cerebral cortex. It is suggested that these changes could contribute to behavioural abnormalities in hyperthyroidism. Similar T3 treatment did not alter abundance of Gi1 alpha or Gi2 alpha in the medulla oblongata nor did it alter abundance of G(o) alpha-subunits in three tested brain regions.

Amino Acid Sequence↗
PubMed1991

Elevated epidermal growth factor receptor binding in plutonium-induced lung tumors from dogs.

The objective of this study is to examine and characterize epidermal growth factor receptor (EGF-R) binding in inhaled plutonium-induced canine lung-tumor tissue and to compare it with that in normal canine lung tissue. Crude membrane preparations from normal and lung-tumor tissue from beagle dogs were examined in a radioreceptor assay, using 125I-labeled epidermal growth factor (EGF) as a ligand. Specific EGF receptor binding was determined in the presence of excess unlabeled EGF. We have examined EGF receptor binding in eight lung-tumor samples obtained from six dogs. Epidermal growth factor receptor binding was significantly greater in lung-tumor samples (31.38%) compared with that in normal lung tissue (3.76%). Scatchard plot analysis from the displacement assay revealed that there was no statistical difference in the binding affinity but significantly higher concentration of EGF-R sites in the lung-tumor tissue (619 fmol/mg) than in normal lung tissue (53 fmol/mg). The increase in EGF-R number in plutonium-induced dog lung tumors does not seem to correlate with increase in the initial lung burden exposure to plutonium. Our results demonstrate that there is a significant increase in EGF-R binding in inhaled plutonium-induced dog lung tumors.

Adenocarcinoma, Papillary↗