Biomedical subjects

T L Yang-Feng

Publications and source records attributed to T L Yang-Feng.

At least 55 records · Page 3Linked to original sources

PubMed1994

Cloning of the human glycine transporter type 1: molecular and pharmacological characterization of novel isoform variants and chromosomal localization of the gene in the human and mouse genomes.

We report the molecular cloning of a cDNA encoding a high affinity human glycine transporter. An open reading frame of 1914 nucleotides encodes a 638-amino acid protein that transports glycine in a Na+/Cl(-)-dependent manner. In common with other Na+/Cl(-)-dependent transporters, it possesses 12 putative transmembrane domains, according to its hydropathicity profile. This protein is the human homologue of a glycine transporter previously isolated from rat [glycine transporter type 1b (GlyT-1b)]. In addition to the human GlyT-1b, we also characterized a novel functional isoform produced by alternative splicing. This isoform, GlyT-1c, which is distinct from GlyT-2 recently characterized in rat, contains an additional exon encoding 54 amino acids in the amino-terminal part of GlyT-1b and is mainly expressed in brain. These two isoforms are products of the same gene and are localized on human chromosome 1p31.3, as well as on mouse chromosome 4, close to the locus for the spontaneous mouse neuromuscular mutation clasper. When expressed in COS-7 cells, both the human GlyT-1b and GlyT-1c display a time- and dose-dependent uptake of glycine, which is abolished when either Na+ or Cl- is substituted with other ions. For both GlyT-1b and GlyT-1c the affinities for glycine are similar, with Km values of 70-90 microM, and this uptake is inhibited by sarcosine with similar potencies. In addition to the three transporter isoforms present in the human genome, i.e., GlyT-1a, GlyT-1b, and GlyT-1c, point-mutated variants, which appear to be totally devoid of glycine uptake activity when expressed in COS-7 cells, were obtained by polymerase chain reaction amplification of mRNA from human substantia nigra. These variants point to regions of the glycine transporter that might be important in the processing or transport function of this protein.

Amino Acid Sequence↗

PubMed1993

Deficient transcription of XIST from tiny ring X chromosomes in females with severe phenotypes.

The severe phenotype of human females whose karyotype includes tiny ring X chromosomes has been attributed to the inability of the small ring X chromosome to inactivate. The XIST locus is expressed only from the inactive X chromosome, resides at the putative X inactivation center, and is considered a prime player in the initiation of mammalian X dosage compensation. Using PCR, Southern blot analysis, and in situ hybridization, we have looked for the presence of the XIST locus in tiny ring X chromosomes from eight females who have multiple congenital malformations and severe mental retardation. Our studies reveal heterogeneity within this group; some rings lack the XIST locus, while others have sequences homologous to probes for XIST. However, in the latter, the locus is either not expressed or negligibly expressed, based on reverse transcription-PCR analysis. Therefore, what these tiny ring chromosomes have in common is a level of XIST transcription comparable to an active X. As XIST transcription is an indicator of X chromosome inactivity, the absence of XIST transcription strongly suggests that tiny ring X chromosomes in females with severe phenotypes are mutants in the X chromosome inactivation pathway and that the inability of these rings to inactivate is responsible for the severe phenotypes.

Adolescent↗

PubMed1993

Allelic loss in ovarian cancer.

Loss of heterozygosity (LOH) was examined at 86 loci distributed on every chromosomal arm in 50 human ovarian tumors. Frequent allele losses were observed on chromosomes 13q (42%), 17p (42%), 17q (45%), and Xp (41%). Deletion mapping on chromosome 17 revealed a candidate gene on the long arm distal to D17S41/S74 for ovarian cancer which is distant from the locus for early onset breast cancer. LOH on chromosome 17q was found to be concordant with LOH on chromosomes 3p, 13q, 17p and Xp suggesting that it may be an early event in neoplastic development. These findings indicate that multiple tumor-suppressor genes for ovarian cancer possibly exist on chromosomes 13q, 17, and/or Xp and provide the basis for the identification of candidate gene(s) associated with ovarian cancer. The chromosomal mechanisms resulting in allele losses in ovarian cancer include deletion, deletion/duplication, mitotic recombination and monosomy, in concordance with the developed genetic model.

Alleles↗

PubMed1993

Molecular and cytogenetic characterization of 9p- abnormalities.

We report on 2 girls with terminal deletion of the short arm of chromosome 9 with concurrent duplication unrecognizable by routine chromosome studies. The phenotype of the patients was not specifically suggestive of the 9p-syndrome in the absence of trigonocephaly and long philtrum as cardinal manifestations. In addition to psychomotor retardation, their manifestations were mild and include upward slant of palpebral fissures and dolichomesophalangy which are characteristic of del(9p). Chromosome abnormalities were de novo in both cases. The two rearranged chromosomes 9 exhibit similar G-banding patterns and suggested the possible duplication of distal 7p. Fluorescence in situ hybridization (FISH) with a chromosome-7 specific library probe indeed identified that one derivative chromosome 9 was the result of a translocation between chromosomes 7 and 9 [der(9)t(7;9)(p15.3;p24] but failed to detect a signal on the other derivative 9. In the second case, the concurrent abnormality was an inverted duplication of proximal 9p and deletion of distal 9p [inv dup(9)(p13-->p22::p22-->qter)] confirmed by FISH using a chromosome 9 specific library probe. FISH clearly identified the origin of these 2 abnormal chromosomes 9 and provided crucial information for clinical evaluation. We emphasize the importance of utilizing updated cytogenetic and molecular techniques in the precise delineation of subtle or complex abnormalities where there are no useful phenotypic clues.

Abnormalities, Multiple↗

PubMed1993

Mosaic dup (9p) diagnosed by fluorescence in situ hybridization (FISH).

We describe a girl with some manifestations of the dup (9p) syndrome. High-resolution Giemsa-banded karyotype of her lymphocytes documented that she was mosaic with 80% of cells being 46,XX, and 20% 46,XX,-20, + der(20;?) (p13;?). The additional material on 20p could not be defined clearly by high-resolution Giemsa banding, as the banding pattern appeared consistent with either distal 9p or distal 13q. In order to make a definitive cytogenetic diagnosis, we used fluorescence in situ hybridization (FISH) with a chromosome 9 specific DNA library to establish that the origin of the additional chromosomal material on chromosome 20 was from 9p. FISH used in this situation enabled us to counsel the family specifically regarding the prognosis and manifestations of distal 9p duplication.

Abnormalities, Multiple↗

PubMed1993

Fetal blood sampling and cytogenetic abnormalities.

From September 1984 to April 1991, we performed cytogenetic analysis on fetal blood samples from 214 second- and third-trimester pregnancies. One hundred and thirty-four cases were referred to consider the possibility of chromosomal mosaicism following amniocyte studies. The confirmation rate of mosaicism is at 0 per cent (0/9), 1.4 per cent (1/70), and 40 per cent (22/55) for cases of level I, level II, and level III mosaicism, respectively. Four out of 17 cases were positive for the diagnosis of fragile X syndrome. Of 63 cases with abnormal ultrasound findings, blood disorders, or other genetically related clinical conditions, 11 were found to have a chromosome abnormality. Fetal blood sampling is a valuable adjunct to other methods in the prenatal diagnosis of chromosomal mosaicism or pseudomosaicism. It is also useful when rapid cytogenetic diagnosis is desired because of malformations detected in pregnancies at a late gestational age.

Cells, Cultured↗

PubMed1993

Follow-up of pregnancies complicated by placental mosaicism diagnosed by chorionic villus sampling.

Thirty-nine (2.3 per cent) of 1724 chromosome studies from diagnostic chorionic villus samplings (CVS) done between 1983 and 1990 showed either level III (true) mosaicism (1.2 per cent) or level II (pseudo-) mosaicism (1.1 per cent) for chromosomal aneuploidy. Follow-up information on these 39 pregnancies was collected from questionnaires to families, paediatricians, and obstetricians. For all cases in which the pregnancy was continued and further testing was accomplished, the mosaicism was felt to be confined to the placenta. As compared with a control group of pregnancies evaluated by CVS with normal karyotypes, there was no increased incidence of pregnancy loss, congenital malformations, or developmental delay in the infants. Although intrauterine growth retardation occurred in several of the level III mosaic cases, adequate catch-up growth has been demonstrated.

Abortion, Spontaneous↗

PubMed1993

Advanced ovarian carcinoma: molecular evidence of unifocal origin.

The clonal origin has sometimes been disputed in advanced epithelial cancers when multiple sites of peritoneal tumors were present because of the developmental similarity of the surface epithelium of the ovary and the peritoneal mesothelium. We have taken two independent approaches to study the clonality of advanced epithelial carcinoma. Tumor samples of both ovaries, and/or omentum, and/or peritoneum from nine patients were examined. The analysis of loss of heterozygosity (LOH) at 86 polymorphic chromosomal loci distributed on every chromosome revealed the loss of the same allele in every tumor of each patient when LOH was detected. In addition, we used a restriction-fragment-length polymorphism in an X-linked sequence (DXS255) to examine the pattern of X-chromosome inactivation based on the differential methylation of DXS255 in active and inactive X chromosomes. Inactivation of the same X chromosome in various tumors from the same patient was observed in each of the five informative patients. Our results strongly suggest that the advanced epithelial cancers are monoclonal in origin.

Adult↗

PubMed1993

Human skeletal muscle insulin receptor substrate-1. Characterization of the cDNA, gene, and chromosomal localization.

Insulin receptor substrate-1 is a major substrate of insulin receptor Tyr kinase. We have now cloned the IRS-1 cDNA from human skeletal muscle, one of the most important target tissues of insulin action, localized and cloned the human IRS-1 gene, and studied the expression of the protein in Chinese hamster ovary cells. Human IRS-1 cDNA encodes a 1242 amino acid sequence that is 88% identical with rat liver IRS-1. The 14 potential Tyr phosphorylation sites include 6 Tyr-Met-X-Met motifs and 3 Tyr-X-X-Met motifs that are completely conserved in human IRS-1. Human IRS-1 has > 50 possible Ser/Thr phosphorylation sites and one potential ATP-binding site close to the NH2-terminal. The human IRS-1 gene contains the entire 5'-untranslated region and protein coding region in a single exon and was localized on chromosome 2 q36-37 by in situ hybridization. By Northern blot analysis, IRS-1 mRNA is rare and consists of two species of 6.9 and 6 kilobase. By using quantitative polymerase chain reaction after reverse transcription of total RNA from human fetal tissues, IRS-1 mRNA could be identified in all tissues. When human IRS-1 cDNA was expressed in Chinese hamster ovary cells, the protein migrated between 170,000-180,000 M(r) in sodium dodecyl sulfate-polyacrylamide gel electrophoresis and was rapidly Tyr phosphorylated upon insulin stimulation. Thus, IRS-1 is widely expressed and highly conserved across species and tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗

PubMed1993

Molecular definition of a chromosome 9p21 germ-line deletion in a woman with multiple melanomas and a plexiform neurofibroma: implications for 9p tumor-suppressor gene(s).

Cutaneous malignant melanoma (CMM) is often familial, but the mode of inheritance and the chromosomal location of melanoma susceptibility locus are controversial. Identification of a 34-year-old woman with eight primary malignant melanomas, multiple atypical moles, and a de novo constitutional cytogenetic rearrangement involving chromosomes 5p and 9p suggested the presence of a melanoma predisposition gene at one of these locations. A high-resolution karyotype showed a partial deletion of a dark-staining Giemsa band, either 5p14 or 9p21. The patient was heterozygous for five 5p14 RFLPs. In situ hybridization with D9S3 indicated that this 9p21 marker was deleted. Gene dosage studies demonstrated the deletion of two more distal 9p21 markers, D9S126 and IFNA. In addition, she was hemizygous for the more proximal 9p21 short tandem-repeat polymorphism at D9S104. D9S18, D9S19, and D9S33 were retained, localizing the deletion to 9p21 between D9S19 on the proximal side and D9S33 on the distal side. Pulsed-field gel electrophoresis with D9S19 and D9S33 did not reveal any junction fragments in the patient's DNA. This germ-line deletion suggests that mutations in a 9p21 gene may initiate melanoma tumorigenesis.

Adult↗

PubMed1992

Smallest terminal deletion of the long arm of chromosome 2 in a mildly affected boy.

We describe a male twin with the smallest terminal deletion of chromosome 2q [46,XY,del(2)(q37.2)] reported to date. His deletion was confirmed by a fluorescence in situ hybridization study using a probe from the deleted region. Only 3 other cases with larger deletions including 2q37.2-->qter have been reported. Clinical manifestations our patient has in common with them include frontal bossing, long eyelashes, micrognathia, infantile hypotonia and developmental delay. His twin brother is physically and developmentally normal and chromosomes of the parents were normal. The mildness of the phenotype in this patient supports less stringent criteria for cytogenetic study of developmentally impaired individuals.

Adult↗

PubMed1992

Frequent loss of heterozygosity on chromosomes Xp and 13q in human ovarian cancer.

Loss of heterozygosity (LOH) was examined at 27 loci on chromosomes 3p, 6q, 11p, 13q, 17 and X in 42 human ovarian tumors. LOH was detected in 12 of 26 (46%) and 5 of 12 (42%) informative cases at 2 chromosome 13q loci, D13S32 and D13S34 respectively. On chromosome Xp, tumor-specific allele loss was observed in 9 out of 15 informative cases (60%) at the ornithine transcarbamylase (OTC) gene locus. Examination of 12 additional Xp and 13q loci has mapped the common deletion regions to Xp21.1-->p11.4 and 13q33-->q34. The observation of significant LOH on Xp represents a strong indication of genetic changes in the X chromosome in a human malignancy. The allele losses on 13q which have been reported for other cancers suggest that chromosome 13, in addition to the retinoblastoma gene, may contain other growth-regulating gene(s) important in the development of several tumor types, including ovarian malignancies.

Chromosome Deletion↗

PubMed1992

Cytogenetic and molecular characterization of marker chromosomes in patients with mosaic 45,X karyotypes.

Cytogenetic and molecular techniques were employed to determine the origin of marker chromosomes in five patients with mosaic 45,X karyotypes. The markers were shown to be derived from the X chromosome in three female patients and from the Y chromosome in one female and one male. One of the female patients, with a very small, X-derived ring chromosome, had additional phenotypic abnormalities not typically associated with Turner syndrome. In this patient, both the ring and the normal X chromosomes replicated early; perhaps the unusual phenotype is the result of both chromosomes remaining transcriptionally active. These studies illustrate the power of resolution and utility of combined cytogenetic and molecular approaches to some clinical cases.

Adolescent↗

PubMed1992

Assignment of the human glycogen debrancher gene to chromosome 1p21.

Glycogen debranching enzyme is a monomeric protein containing two independent catalytic activities of glycantransferase and glucosidase that are both required for glycogen degradation. Its deficiency causes type III glycogen storage disease. A majority of the patients with this disease have deficient enzyme activity in both liver and muscle (type IIIa) but approximately 15% of them lack enzyme activity only in the liver (type IIIb); however, the enzyme is a monomer and appears to be identical in all the tissues. The cDNA coding for the complete human muscle debranching enzyme has recently been isolated. Using the cDNA clones, the debrancher gene was localized to human chromosome 1 by somatic cell hybrid analysis. Regional assignment to chromosome band 1p21 was determined by in situ hybridization. Mapping of the debrancher gene to a single chromosome site is consistent with our hypotheses that a single gene encodes both liver and muscle debrancher protein.

Animals↗

PubMed1992

Colocalization of the genes for the alpha 3(IV) and alpha 4(IV) chains of type IV collagen to chromosome 2 bands q35-q37.

Each type of basement membrane in man contains between two and five genetically distinct type IV collagens: alpha 1(IV)-alpha 5(IV). Genes for alpha 1(IV), alpha 2(IV), alpha 3(IV), and alpha 5(IV) have been isolated. We have recently isolated partial cDNAs for the fifth member of the family, designated alpha 4(IV). On the basis of comparison of the deduced peptide sequences of all five chains, the type IV collagens can be divided into two families: alpha 1-like, comprising alpha 1(IV), alpha 3(IV), and alpha 5(IV); and alpha 2-like, comprising alpha 2(IV) and alpha 4(IV). Genes encoding the alpha 1(IV) and alpha 2(IV) chains (COL4A1 and COL4A2) both map to human chromosome 13q34 and have been shown to be transcribed from opposite DNA strands using a common bidirectional promoter that allows coordinate regulation of the two chains. Indeed, these two chains are commonly found together in basement membrane and form [alpha 1]2.[alpha 2] heterotrimers. Whereas alpha 1(IV) and alpha 2(IV) have been found in all basement membranes studied hitherto, it has been shown that alpha 3(IV) and alpha 4(IV) are found in only a subset of basement membranes. In basement membranes where either of these molecules is present, however, they are found together. In view of this relationship and the structural similarities between alpha 1(IV) and alpha 3(IV) and between alpha 2(IV) and alpha 4(IV), we hypothesized that COL4A3 and COL4A4, the genes encoding alpha 3(IV) and alpha 4(IV), respectively, have a genomic organization similar to that of COL4A1 and COL4A2.(ABSTRACT TRUNCATED AT 250 WORDS)

Basement Membrane↗

PubMed1992

Assignment of two human alpha-1,3-galactosyltransferase gene sequences (GGTA1 and GGTA1P) to chromosomes 9q33-q34 and 12q14-q15.

alpha-1,3-Galactosyltransferase is a terminal glycosyltransferase that is widely expressed in a variety of mammalian species, with the notable exception of man, apes, and Old World monkeys. Although transcripts for this enzyme are not detectable in humans, homologous sequences have been identified in human genomic DNA. These sequences correspond to a processed pseudogene that maps to chromosome 12 and the inactivated remnant of the once functional source gene that maps to chromosome 9. We have now established that the former sequence (GGTA1P) is localized to 12q14-q15 and the latter sequence (GGTA1) is localized to 9q33-q34 [corrected].

Chromosome Banding↗

PubMed1992

Neural retina-specific leucine zipper gene NRL (D14S46E) maps to human chromosome 14q11.1-q11.2.

The product of a neural retina-specific gene, NRL, belongs to the "leucine zipper" family of DNA-binding proteins and has a strong similarity to the v-maf oncogene product. The NRL gene maps to human chromosome 14 by Southern blot analysis of genomic DNA from a human-rodent somatic cell hybrid panel. In situ hybridization to metaphase chromosomes has further sublocalized the gene to the region 14q11.1-q11.2. D14S46E has now been assigned to the NRL gene. Because of its specific pattern of expression, NRL is a candidate gene for retinal diseases.

Animals↗

PubMed1992

Molecular isolation and characterization of an expressed gene from the human Y chromosome.

Using a positional cloning approach, we have isolated an expressed gene from a flow-sorted Y chromosome cosmid library. The isolation of this gene was based on the identification of the Y-231 cosmid that contains CpG rich sequences (HTF islands) in its human insert. The Y-231 cosmid was capable of detecting a 1.3 kb transcript in poly (A)+ RNA samples from human testis. Several cDNA clones were isolated from a human testis cDNA library constructed in lambda gt10. In addition, DNA-mediated gene transfer and restriction enzyme mapping experiments demonstrated that two functional transcriptional units are present within the Y-231 cosmid. DNA sequencing analysis showed that the largest cDNA clone contains 1075 bp of unique sequence and a poly (A) track at the 3' end of the corresponding mRNA. An open reading frame of 762 bp that encodes a predicted protein of 253 amino acids with a calculated molecular weight of 28.9 kD was identified. The Y-231 structural gene encompasses approximately 2.7 kb of genomic sequence and contains six exons that are interrupted by five introns. The Y-231 gene shares very high (97%) identity at the DNA level to a previously described Y-specific gene, testis specific protein Y-encoded (TSPY) gene, suggesting the possibility that these two genes are related, if not identical. However, the TSPY gene has been postulated to be intronless. Further PCR and RT-PCR analyses of these two genes and their transcripts have provided evidence supporting the hypothesis that they are the same gene and are members of a Y-specific repeated gene family containing intronic sequences. The Y-231 (TSPY) gene is conserved in the male genome and expressed in the testis of the chimpanzee, suggesting that it may play an important role in the physiology of this organ in man and the great ape.

Amino Acid Sequence↗