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Biomedical subjects

S H Phua

Publications and source records attributed to S H Phua.

At least 19 recordsLinked to original sources
PubMed1999

A diagnostic assay discriminating between two major Ovis aries mitochondrial DNA haplogroups.

Two major Ovis aries mitochondrial DNA (mtDNA) haplogroups have been described in independent studies. HinfI RFLP data of mitochondrial genomes from a large sample set (n = 239) indicated an ancient mutation which differentiates between the two mtDNA types. A completely determined sheep mtDNA sequence was used to assign this mutation to the COI gene and to develop a PCR based assay discriminating between the two phylogenetic branches. The haplogroup specificity of the mutation was further investigated in 26 randomly selected individuals. The animals were unequivocally assigned to their respective groups on the basis of the developed test and their complete control region sequences. The assay provides a rapid and economic means of discriminating between both major domestic sheep mtDNAs.

Animals↗
PubMed1999

Isolation and mapping of the first ruminant multidrug resistance genes.

The first ruminant multiple drug resistance gene (MDR1) has been cloned and sequenced from sheep. Sequence data revealed the sheep MDR1 gene to have high sequence and structural similarity to other characterized MDR proteins from humans and rodents. A restriction fragment length polymorphism was discovered using the EcoRI enzyme and used to map the MDR1 gene to sheep chromosome 4. Physical mapping using fluorescent in situ hybridisation confirmed this map placement and assigned the MDR1 locus in the region 4q15-q21. The ovine MDR2 gene was also cloned and found to map to the same region as MDR1.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed1999

Catalase gene is associated with facial eczema disease resistance in sheep.

Facial eczema (FE) is a hepatogenous photosensitization disease of ruminant animals, particularly in sheep which vary widely in their susceptibility to the disease. The liver damage is caused by the mycotoxin, sporidesmin. There is evidence that the toxicity of sporidesmin is due to its ability to generate 'active oxygen' species. We evaluated the catalase gene, which encodes an enzyme with antioxidant functions, as a candidate for determining the susceptibility of sheep to the disease. Two microsatellite markers, OarSHP3 and OarSHP4, which flank the sheep catalase gene, were isolated from a Yeast Artificial Chromosome (YAC) clone. These markers mapped the catalase locus by linkage to ovine chromosome 15. Eleven informative markers spaced throughout chromosome 15, inclusive of the catalase marker OarSHP4, gave no significant linkage with the disease traits when analysed in four outcross resource pedigrees. However, OarSHP3 and OarSHP4 allele frequencies showed significant differences between FE resistant and susceptible selection-lines. Comparison of sequences of catalase cDNAs from sheep of resistant and susceptible lines showed only two silent mutations. A single nucleotide polymorphisms (KP1) in exon 6 of the catalase gene also showed significant differences in allele frequencies between the selection lines. The lack of evidence for linkage in outcross pedigrees, but the significant association in the genetic lines, implies that catalase is involved in determining the susceptibility of sheep to facial eczema, and that the candidate gene's effect is probably recessive or minor.

Alleles↗
PubMed1996

Variation in the control region sequence of the sheep mitochondrial genome.

The DNA sequences of the control region of the mitochondrial genome of fifty unrelated sheep were determined in order to ascertain the extent and distribution of its variability. A consensus sequence was derived, and 1081 differences from it were observed amongst the fifty animals. Some constant groups of differences were observed that were held in common by a number of animals, which thus fell into two main groups, although neither group was typical of any of the breeds sampled. The consensus sequence also allowed comparison between the control region sequences of sheep and other mammals. The sequence contains four tandem repeats of a 75 base-pair motif that accounts for the difference in its size from the cattle control region, to which it is otherwise very similar. Comparison with the cattle sequence allowed the determination of the homologues of various functionally important sites. The homologues of the transcription promoters, the origin of replication and the central conserved sequence block were all identified by this method.

Animals↗
PubMed1995

Cloning of a DNA repeat element from horse: DNA sequence and chromosomal localization.

A DNA repeat element, revealed initially by digestion of horse DNA with TaqI, was cloned and characterized by Southern and in situ hybridization studies and nucleotide sequencing. The clone, e4/1, consisted of 32 tandem reiteration of a unit repeat of 21-22 bp, and produced multilocus DNA fingerprinting profiles that were useful for parentage analysis in horses. The tandem repeat element was shown by in situ hybridization to be localized in the centromeres of the acrocentric but not metacentric classes of horse chromosomes.

Animals↗
PubMed1995

Families of tandemly repeated DNA elements from horse: cloning, nucleotide sequence, and organization.

DNA repeats, revealed initially by digestion of horse DNA with restriction enzymes, were cloned and characterized by cross-hybridization studies and nucleotide sequencing. The Sau-like family of tandem repeats contained two classes of repetitive elements with unit repeats of about 80 bp that shared no sequence similarity. Both unit repeats were present, frequently in tandem, in cloned segments of horse DNA of less than 600 bp. Evidence is presented, based on their ladderlike patterns of hybridization to horse DNA and their high level of similarity to published sequences of satellites from equine DNA, suggesting that they are centromerically located in the horse genome. The Sau-like tandem repeat families were specific to Equidae. Another class of repeats, GATA-like elements, which did not appear to have a centromeric distribution, was also cloned and sequenced.

Animals↗
PubMed1994

Regional mapping of loci from human chromosome 2q to sheep chromosome 2q.

The human chromosome 2q loci, fibronectin 1 (FN1), the alpha 1 chain of type III collagen (COL3A1), and the delta subunit of the muscle acetylcholine receptor (CHRND) have been regionally assigned to sheep chromosome 2q by in situ hybridization. COL3A1 is pericentromeric (2q12-q21), while FN1 and CHRND are in the subterminal region at 2q41-q44 and 2q42-qter, respectively. The mapping of FN1 assigns the sheep syntenic group U11, which contains FN1, villin 1 (VIL1), isocitrate dehydrogenase 1 (IDH1), and gamma subunit of the muscle acetylcholine receptor (CHRNG), to sheep chromosome 2q. Inhibin-alpha (INHA) is also assigned to sheep chromosome 2q as FN1 and INHA compose sheep linkage group 3. These seven loci are members of a conserved chromosomal segment in human, mouse, and sheep.

Animals↗