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Biomedical subjects

Frederick C Leung

Publications and source records attributed to Frederick C Leung.

8 recordsLinked to original sources
PubMed2006

The intragenomic polymorphism of a partially inverted repeat (PIR) in Gallus gallus domesticus, potential role of inverted repeats in satellite DNAs evolution.

We report here the molecular characterization of the basic repeating unit of a novel repetitive family, partially inverted repeat (PIR), previously identified from chicken genome. This repetitive DNA family shares a close evolutionary relationship with XhoI/EcoRI repeats and chicken nuclear-membrane-associated (CNM) repeat. Sequence analyses reveal the 1430 bp basic repeating unit can be divided into two regions: the central region ( approximately 1000 bp) and the flanking region ( approximately 430 bp). Within the central region, a pair of repeats (86 bp) flanks the central core ( approximately 828 bp) in inversed orientation. Due to the tandem array feature shared by the repeating units, the inverted repeats fall between the central core and flanking region. Southern blot analyses further reveal the intragenomic polymorphism of PIR, and the molecular size of repeating units ranges from 1.1 kb to 1.6 kb. The identified monomer variants may result from multiple crossing-over events, implying the potential roles of inverted repeats in satellite DNAs variation.

Animals↗
PubMed2006

Molecular characterization of foot-and-mouth disease virus in Hong Kong during 2001-2002.

Most of the molecular epidemiological studies of foot-and-mouth disease virus (FMDV) are based on comparison of VP1 gene sequence. In this report, The nucleotide sequences of the VP1 coding region of FMDV type O strains O/HKN/3/01, O/HKN/5/01, O/HKN/12/01, O/HKN/7/02 and O/HKN/10/02, isolated from the disease outbreak that occurred in Hong Kong Special Administrative Region (Hong Kong SAR) of China during 2001-2002, were determined and compared with the sequences of other FMDVs. The results revealed that the VP1 gene of the five isolates had the same nucleotide (nt) sequences (639 nt), coding for 213 amino acids, and no changes were found either at the critical amino acid sites 144 (Val), 148 (Leu), 154 (Lys) and 208 (Pro) within the VP1 protein epitope (amino acids 140-160, 200-213), or in the amino acids 145-147 comprising the arginine-glycine-aspartic acid (RGD) sequence that is involved in the adsorption of virus to host cell. Analysis of the VP1 gene nucleotide sequence revealed that the five isolates examined were most closely related to FMDVs found in Hong Kong from 1991 to 1999 and Taiwan in 1997. Furthermore, although the critical amino acids on the antigen epitope of the prevalent Hong Kong isolates and the serotype O vaccine strain, O1/Manisa/Turkey/69, showed relative conservativeness, they were distantly related genetically, which showed that there existed variation between the prevalent Hong Kong FMDV strains and the vaccine strain.

Amino Acid Sequence↗
PubMed2006

A CR1 element is embedded in a novel tandem repeat (HinfI repeat) within the chicken genome.

Highly repetitive DNA sequences constitute a significant portion of most eukaryotic genomes, raising questions about their evolutionary origins and amplification dynamics. In this study, a novel chicken repetitive DNA family, the HinfI repeat, was characterized. The basic repeating unit of this family displays a uniform length of 770 bp, which was defined by the recognition site of HinfI. The HinfI repeat was specifically localized in the pericentric region of chromosome 4 by fluorescence in situ hybridization and constitutes 0.51% of the chicken genome. Interestingly, a chicken repeat 1 (CR1) element has been identified within this basic repeating unit. Like other CR1 elements, this CR1 element also displays typical retrotransposition characteristics, including a highly conserved 3' region and a badly truncated 5' end. This direct evidence from sequence analysis, together with our Southern blot results, suggests that the HinfI repeat may originate from a unique region containing a retrotransposed CR1 element.

Animals↗
PubMed2004

Rapid authentication of ginseng species using microchip electrophoresis with laser-induced fluorescence detection.

Ginseng is one of the most expensive Chinese herbal medicines and the effectiveness of ginseng depends strongly on its botanical sources and the use of different parts of the plants. In this study, a microchip electrophoresis method coupled with the polymerase chain reaction (PCR)-short tandem repeats (STR) technique was developed for rapid authentication of ginseng species. A low viscosity hydroxypropyl methylcellulose (HPMC) solution was used as the sieving matrix for separation of the amplified STR fragments. The allele sizing of the amplified PCR products could be detected within 240 s or less. Good reproducibility and accuracy of the fragment size were obtained with the relative standard deviation for the allele sizes less than 1.0% (n=11). At two microsatellite loci (CT 12, CA 33), American ginseng had a different allele pattern on the electropherograms compared with that of the Oriental ginseng. Moreover, cultivated and wild American ginseng can be distinguished on the basis of allele sizing. This work establishes the feasibility of fast genetic authentication of ginseng species by use of microchip electrophoresis.

Alleles↗
PubMed2004

Characterization of the 5'-flanking transcriptional regulatory region of chicken growth hormone gene.

A 1727-bp fragment of 5'-flanking region of chicken growth hormone (cGH) gene has been cloned and sequenced. Various lengths of the 5'-flanking region (122 to 1775 bp) was linked to a luciferase reporter gene, and its transcriptional regulation was examined by an in vitro transient transfection coupled with luciferase assay. Our results demonstrated that pituitary-specific transcription factor, Pit-1, is necessary and sufficient to confer a strong tissue-specific expression. Co-transfection with goldfish or chicken Pit-1 expression vectors significantly restored the luciferase expression in HeLa cells. Site-directed mutagenesis and mobility gel-shift assays further confirmed the position of the Pit-1 binding site at -113/-104. Moreover, a repressive thyroid hormone response element (TRE) was identified at -137/-74, and we propose that interactions between the TRE and Pit-1 sites may be required for its repressive effect.

5' Untranslated Regions↗
PubMed2002

Partially inverted tandem repeat isolated from pericentric region of chicken chromosome 8.

The majority of chicken repetitive sequence is nuclear-membrane-associated sequence (CNM), which resides in a large number of microchromosomes (chromosomes 11-39) and is absent from macrochromosomes 1-5, ZW, and some of the intermediate chromosomes 6-10. Two repetitive families, EcoRI/XhoI, are confined to the female-specific W chromosome. The core repeat units of the three families are 21 bp, containing (A)3-5 and (T)3-5 clusters separated by 5-7-bp sequences. In this article, we describe the isolation and initial characterization of a novel repeat family that is related to CNM/EcoRI/XhoI families. The novel family, designated as PIR, consists of multiple types of partially inverted repeat units of about 1.2, 1.4 and 1.6 kb. The PIR sequence is restricted to chicken chromosome 8, and accounts for about 3.8 mb, or 2500 copies of the 1.4-kb units, of the chicken genome. The evolution of PIR and related sequences is discussed.

Animals↗