Search PubMed⌕ Search

Biomedical subjects

K H Choo

Publications and source records attributed to K H Choo.

At least 91 records · Page 5Linked to original sources
PubMed1991

Four distinct alpha satellite subfamilies shared by human chromosomes 13, 14 and 21.

We describe the characterisation of four alpha satellite sequences which are found on a subset of the human acrocentric chromosomes. Direct sequence study, and analysis of somatic cell hybrids carrying specific human chromosomes indicate a unique 'higher-order structure' for each of the four sequences, suggesting that they belong to different subfamilies of alpha DNA. Under very high stringency of Southern hybridisation conditions, all four subfamilies were detected on chromosomes 13, 14 and 21, with 13 and 21 showing a slightly greater sequence homology in comparison to chromosome 14. None of these subfamilies were detected on chromosomes 15 and 22. In addition, we report preliminary evidence for a new alphoid subfamily that is specific for human chromosome 14. These results, together with those of earlier published work, indicate that the centromeres of the five acrocentric chromosomes are characterised by a number of clearly defined alphoid subfamilies or microdomains (with at least 5, 7, 3, 5 and 2 different ones on chromosomes 13, 14, 15, 21 and 22, respectively). These microdomains must impose a relatively stringent subregional pairing of the centromeres of two homologous chromosomes. The different alphoid subfamilies reported should serve as useful markers to allow further 'dissection' of the structure of the human centromere as well as the investigation of how the different nonhomologous chromosomes may interact in the aetiology of aberrations involving these chromosomes.

Blotting, Southern↗
PubMed1991

The importance of further cytogenetic and molecular investigation of acrocentric variants: justification by presentation of a case [t(8;14)(q24;p11)].

On routine chromosome analysis a moderately retarded 18-year-old man was found to have an unusual short arm on one chromosome 14. With GTL-banding this chromosome showed an enlarged short arm with no evident secondary constriction. Negative CBG-banding of the short arm suggested the possibility of a translocation involving euchromatin. Interpretation of the abnormality as an unbalanced translocation relied on chromosome analysis using GTL-, CBG-, and Ag-NOR-banding of the proband's phenotypically normal mother, who was found to be carrying a balanced translocation involving chromosomes 8 and 14. In situ hybridization of sequences known to map to the short arm of chromosome 14 confirmed the interpretation and established that the breakpoint was within p11. The patient, whose karyotype is 46,XY, -14, +der(14)t(8;14)(q24.1;p11), is trisomic for the terminal end of the long arm of chromosome 8. The patient's clinical features are described and compared with those reported in patients trisomic for this region. This study demonstrates the importance of using a number of different banding techniques in conjunction with in situ hybridization for the investigation of morphologically unusual acrocentric short arm variants seen at routine diagnosis.

Adolescent↗
PubMed1990

A homologous subfamily of satellite III DNA on human chromosomes 14 and 22.

We describe a new subfamily of human satellite III DNA that is represented on two different acrocentric chromosomes. This DNA is composed of a tandemly repeated array of diverged 5-base-pair monomer units of the sequence GGAAT or GGAGT. These monomers are organised into a 1.37-kilobase higher-order structure that is itself tandemly reiterated. Using a panel of somatic cell hybrids containing specific human chromosomes, this higher-order structure is demonstrated on chromosomes 14 and 22, but not on the remaining acrocentric chromosomes. In situ hybridisation studies have localised the sequence to the proximal p-arm region of these chromosomes. Analysis by pulsed-field gel electrophoresis (PFGE) reveals that 70-110 copies of the higher-order structure are tandemly organised on a chromosome into a major domain which appears to be flanked on both sides by non-tandemly repeated genomic DNA. In addition, some of the satellite III sequences are interspersed over a number of other PFGE fragments. This study provides fundamental knowledge on the structure and evolution of the acrocentric chromosomes, and should extend our understanding of the complex process of interchromosomal interaction which may be responsible for Robertsonian translocation and meiotic nondisjunction involving these chromosomes.

Animals↗
PubMed1990

Identification of two distinct subfamilies of alpha satellite DNA that are highly specific for human chromosome 15.

We report the isolation of two distinct subfamilies of alpha satellite DNA (pTRA-20 and -25) from human chromosome 15. In situ hybridization experiments indicated that both subfamilies are highly specific for this chromosome. Southern analysis of a somatic hybrid cell line carrying human chromosome 15 revealed a likely higher-order genomic band of 2.5 kb for pTRA-20. Similar analysis for pTRA-25 showed multiple higher-order bands of 3.5, 4.5, and 5 kb at moderately high hybridization stringency, but a predominance of the 4.5-kb species at very high stringency. Direct comparison with human genomic DNA confirmed the authenticity of these higher-order structures and demonstrated polymorphic variations using both probes. The origin of the different alphoid subfamilies on chromosome 15 is discussed. These sequences should be useful for the construction of centromere-based genetic linkage maps for human chromosome 15 and, in conjunction with the other alphoid sequences already reported for chromosomes 13, 14, 21, and 22, should allow a concerted analysis of the evolution and the possible etiological role of these DNAs in aberrations commonly seen in these chromosomes.

Blotting, Southern↗
PubMed1990

Role of acrocentric cen-pter satellite DNA in Robertsonian translocation and chromosomal non-disjunction.

The centromeres and short arms of the human acrocentric chromosomes have in common several families of tandemly repeated DNA. Recent analyses have revealed that, within some of these families, clearly distinct subfamilies have evolved that are unique to one or a subset of the different acrocentric chromosomes. The existence and maintenance of subfamilies common to different chromosomes entail a process of regular exchange between the non-homologous chromosomes. This process is suggested for the evolution of an alpha satellite subfamily recently found on chromosomes 13, 14 and 21. The presence of this alpha subfamily may allow pairing between these chromosomes leading to the observed non-random participation of these chromosomes in t(13q14q) and t(14q21q) Robertsonian translocations. The available data also indicate a very similar molecular organisation of the cen-pter region for chromosomes 13 and 21. This latter feature may further allow the two chromosomes to undergo a relatively extensive degree of meiotic pairing (in a manner analogous to that seen in the pseudoautosomal regions of the X and Y chromosomes), thus predisposing these two chromosomes to errors in meiotic segregation and non-disjunction.

Centromere↗
PubMed1989

Centromeric alpha satellite DNA amplification and translocation in an unusually large chromosome 14p+ variant.

We report cytogenetic and molecular studies on a family that carries, in the father, an unusually large chromosome 14p+ variant [WSi-var(14)(p+)] and, in one of his children, a translocation [DSi-der(14)] involving the variant chromosome. Increase in the size of WSi-var(14)(p+) was estimated to be approximately 35% that of a normal chromosome 14. Presence of extra chromosomal material in this variant chromosome was demonstrated by G-banding using trypsin and staining with Leishman, G-banding using bromodeoxyuridine (BrdU) and Giemsa, and R-banding using BrdU and Giemsa. This material was positive using C-banding with BaOH and staining with Giemsa and negative in DAPI/distamycin staining, suggesting that it contained repetitive DNA but probably not of the types found in the heterochromatic regions of chromosomes 1, 9, 15, 16, and Y. Staining of the nucleolus organiser region (NOR) with AgNO3 indicated the retention of the NOR in WSi-var(14)(p+) but not in DSi-der(14). In situ hybridisation of metaphase cells with an alpha satellite DNA probe specific for human acrocentric chromosomes demonstrated a significantly increased amount of centromeric alpha sequences in WSi-var(14)(p+). Most or all of the extra alpha sequences were retained in DSi-der(14), indicating translocation near the very distal end of the enlarged region. The extra alpha satellite DNA material may have originated through amplification of some centromeric segments. The possible role of the amplified DNA in chromosomal translocations is discussed.

Chromosome Banding↗
PubMed1989

Amplification of satellite III DNA in an unusually large chromosome 14p+ variant.

A phenotypically normal male (WSm) was found to have an unusually large short arm of chromosome 14. Increase in the size of this variant chromosome [Wsm-var(14)] was estimated to be approximately 30% that of a normal chromosome 14 by G-banding using trypsin and staining with Leishman. The extra chromosomal material was positive in CBG staining (C-banding using BaOH and staining with Giemsa), suggesting the presence of repetitive DNA. In situ hybridisation using repetitive probes demonstrated this material to be strongly positive for satellite III DNA, and negative for Y-specific heterochromatic DNA. Hybridisation with an alpha DNA probe specific for human acrocentric chromosomes indicated the retention of the centromere, and the absence of alpha DNA in the extra chromosomal material. We propose the origin of the extra chromosomal material in WSm-var(14) to be a result of amplification of contiguous satellite III DNA that is normally present in the short arm of chromosome 14. This variant chromosome does not appear to be associated with the abnormal phenotype in WSm's daughter who is mentally retarded and carries a t(1;?)(q41;?) translocation of chromosome 1.

Chromosome Banding↗
PubMed1989

Mouse major (gamma) satellite DNA is highly conserved and organized into extremely long tandem arrays: implications for recombination between nonhomologous chromosomes.

We have isolated and sequenced 30 independent clones derived from MnlI digestion of purified mouse major (gamma) satellite DNA. These clones contained between 0.9 and 1.1 gamma monomeric units derived presumably from random chromosomal sources. Individual clones showed a mean deviation from the mouse consensus satellite sequence of 3.9%, with a range of 0.9-9.1%. Cleavage of total mouse LTK cell genomic DNA with three different restriction enzymes (HindIII, BglII, BamHI) that do not cut within satellite monomers, followed by Southern and pulsed-field gel electrophoretic analyses, showed that the majority of monomers were organized into largely uninterrupted arrays that varied from a minimum of 240 kb to greater than 2000 kb in length. We suggest that the high degree of conservation of the mouse gamma-satellite sequences throughout the mouse genome results from frequent recombinational exchange between nonhomologous chromosomes. Further, this same process, facilitated by the all-acrocentric constitution of the typical mouse karyotype, and the extremely long and homologous gamma-satellite arrays, may be related to the common occurrence of Robertsonian translocation in mouse.

Animals↗
PubMed1989

Evolution of alpha-satellite DNA on human acrocentric chromosomes.

In situ hybridization of five new and one previously described alpha-satellite sequences isolated from chromosome 21 libraries gave the following chromosomal distribution patterns: (a) two sequences (pTRA-1 and -4) hybridizing to chromosomes 13, 14, 15, 21, and 22 (also 19 and 20); (b) one sequence (pTRA-7) hybridizing to chromosome 14; and (c) three sequences (pTRA-2, -11 and -15) hybridizing to chromosomes 13, 14, and 21, with significant but weaker signals on 15 and 22. These results suggested the sharing of alphoid domains between different acrocentric chromosomes and the coexistence of multiple domains on each chromosome. Analysis of somatic cell hybrids carrying a single human acrocentric chromosome using pTRA-2 demonstrated a higher-order repeating structure common to chromosomes 13, 14, and 21, but not to 15 and 22, providing direct evidence for sequence homogenization in this domain among the former three chromosomes. We present a model of evolution and genetic exchange of alpha sequences on the acrocentric chromosomes which can satisfactorily explain these and previous observations of (a) two different alphoid subfamilies, one common to chromosomes 13 and 21 and the other common to chromosomes 14 and 22, (b) a different alphoid subfamily on chromosome 22, and (c) nonrandom participation of chromosomes 13 and 14, and 14 and 21 in Robertsonian translocations.

Blotting, Southern↗
PubMed1988

Homologous alpha satellite sequences on human acrocentric chromosomes with selectivity for chromosomes 13, 14 and 21: implications for recombination between nonhomologues and Robertsonian translocations.

We report a new subfamily of alpha satellite DNA (pTRA-2) which is found on all the human acrocentric chromosomes. The alphoid nature of the cloned DNA was established by partial sequencing. Southern analysis of restriction enzyme-digested DNA fragments from mouse/human hybrid cells containing only human chromosome 21 showed that the predominant higher-order repeating unit for pTRA-2 is a 3.9 kb structure. Analysis of a "consensus" in situ hybridisation profile derived from 13 normal individuals revealed the localisation of 73% of all centromeric autoradiographic grains over the five acrocentric chromosomes, with the following distribution: 20.4%, 21.5%, 17.1%, 7.3% and 6.5% on chromosomes 13, 14, 21, 15 and 22 respectively. An average of 1.4% of grains was found on the centromere of each of the remaining 19 nonacrocentric chromosomes. These results indicate the presence of a common subfamily of alpha satellite DNA on the five acrocentric chromosomes and suggest an evolutionary process consistent with recombination exchange of sequences between the nonhomologues. The results further suggests that such exchanges are more selective for chromosomes 13, 14 and 21 than for chromosomes 15 and 22. The possible role of centromeric alpha satellite DNA in the aetiology of 13q14q and 14q21q Robertsonian translocations involving the common and nonrandom association of chromosomes 13 and 14, and 14 and 21 is discussed.

Base Sequence↗
PubMed1988

Isolation of human chromosome 21 sequences and their application to in situ hybridization.

We report the isolation of 50 independent unique sequences from a human chromosome 21 library (identification code LA21 NSO1). These sequences were individually assigned to chromosome 21 using a mouse-human somatic hybrid cell line, WAVR 4d-F94a. Use of these unique clones as a mixture of probes for in situ hybridization of human metaphase chromosomes demonstrated strong signals on chromosome 21. These unique DNA sequences should provide useful tools for structural and functional analysis of human chromosome 21. The use of these sequences for the detection of Down syndrome is discussed.

Animals↗
PubMed1988

Application of DNA-DNA hybridization of dual labeled probes to the detection of trisomy 21, monosomy 21, and sex determination.

Chromosomal aneuploidy is usually identified by cytogenetic methods. However, for some purposes it would be desirable to have an easier method of recognizing specific trisomies or monosomies. We have devised such an assay. It involves the simultaneous hybridization of two chromosome-specific DNA probes labeled with different isotopes (32P and 35S) to human chromosomal DNA immobilized on a nitrocellulose filter. The hybridization signals are then counted, and the dpm ratios between the two isotopes are determined. In this paper we show the application of this technique in sex determination, in the analysis of two human cell lines reported to have chromosome 21 monosomy, and, especially, in testing for Down syndrome.

Cell Line↗
PubMed1987

Expression of active human blood clotting factor IX in transgenic mice: use of a cDNA with complete mRNA sequence.

Haemophilia B is a bleeding disorder caused by a functional deficiency of the clotting factor IX. A full length human factor IX complementary DNA clone containing all the natural mRNA sequences plus some flanking intron sequences was constructed with a metallothionein promoter and introduced into transgenic mice by microinjection into the pronuclei of fertilised eggs. The transgenic mice expressed high levels of messenger RNA, gamma-carboxylated and glycosylated protein, and biological clotting activity that are indistinguishable from normal human plasma factor IX. This study demonstrates the feasibility of expressing highly complex heterologous proteins in transgenic mice. It also provides the groundwork for the production of large amounts of human factor IX in larger transgenic livestock for therapeutic use, and the investigation of alternative genetic therapies for haemophilia B.

Animals↗