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X N Chen

Publications and source records attributed to X N Chen.

At least 37 records · Page 2Linked to original sources
PubMed1998

JH8, a gene highly homologous to the mouse jerky gene, maps to the region for childhood absence epilepsy on 8q24.

Insertional inactivation of the jerky gene in transgenic mice resulted epileptic seizures, suggesting that the jerky gene was responsible for mouse epilepsy. To isolate a human homologue of the jerky gene, we screened an Expressed Sequence Tag (EST) database using the cDNA sequence of the mouse jerky gene and identified several EST clones which contained homologous sequences to mouse jerky gene. Using a clone which showed highest homology as a probe, we isolated cDNA clones from a human fetal brain cDNA library. Sequence analysis of these clones named JH8 (jerky homologue of Human on chromosome 8) indicated that it encoded a putative protein with 520 amino acid residues. The JH8 gene has 77% identity to the mouse jerky gene at the DNA level, and its protein has 76% identity and 84% similarity to the mouse protein at the amino acid level. Northern blot analysis showed that the JH8 gene is expressed ubiquitously with a major transcript of about 9.5 kb in size. Fluorescence in situ Hybridization (FISH) analysis and radiation hybrid panel mapping revealed that the JH8 gene was located on chromosome band 8q24.3 in a region that was syntenic to mouse chromosome 15, the mapping site of the mouse jerky gene. Childhood Absence Epilepsy (CAE), one type of Idiopathic Generalized Epilepsy (IGE), has been mapped to chromosome 8q24.3 by linkage analysis. These results suggest that JH8 is a strong candidate gene for CAE.

Animals↗
PubMed1998

DSCAM: a novel member of the immunoglobulin superfamily maps in a Down syndrome region and is involved in the development of the nervous system.

Down syndrome (DS), a major cause of mental retardation, is characterized by subtle abnormalities of cortical neuroanatomy, neurochemistry and function. Recent work has shown that chromosome band 21q22 is critical for many of the neurological phenotypes of DS. A gene, DSCAM (Down syndrome cell adhesion molecule), has now been isolated from chromosome band 21q22.2-22.3. Homology searches indicate that the putative DSCAM protein is a novel member of the immunoglobulin (Ig) superfamily that represents a new class of neural cell adhesion molecules. The sequence of cDNAs indicates alternative splicing and predicts two protein isoforms, both containing 10 Ig-C2 domains, with nine at the N-terminus and the tenth located between domains 4 and 5 of the following array of six fibronectin III domains, with or without the following transmembrane and intracellular domains. Northern analyses reveals the transcripts of 9.7, 8.5 and 7.6 kb primarily in brain. These transcripts are differentially expressed in substructures of the adult brain. Tissue in situ hybridization analyses of a mouse homolog of the DSCAM gene revealed broad expression within the nervous system at the time of neuronal differentiation in the neural tube, cortex, hippocampus, medulla, spinal cord and most neural crest-derived tissues. Given its location on chromosome 21, its specific expression in the central nervous system and neural crest, and the homologies to molecules involved in neural migration, differentiation, and synaptic function, we propose that DSCAM is involved in neural differentiation and contributes to the central and peripheral nervous system defects in DS.

Amino Acid Sequence↗
PubMed1997

The structure and chromosome location of the human chondroadherin gene (CHAD).

The cDNA sequence of the human chondroadherin gene was cloned using PCR-based techniques. The gene encodes a protein of 359 amino acids, of which the first 21 amino acids represent a putative signal peptide sequence and which possesses 11 leucine-rich repeats flanked by cysteine-rich regions. The cDNA possesses a 5' untranslated region of 149 bp, a coding region of 1080 bp including the stop codon, and a 3' untranslated region of 561 bp terminating in a poly(A) tail. The cDNA hybridizes with a single messenger RNA of 1.9 kb, which is present in chondrocytes at all ages. Analysis of genomic DNA revealed that the chondroadherin gene possesses two introns, both of which reside within the coding region. The first intron has a length of about 2.3 kb and separates the codons for lysine(258) and phenylalanine(259). The second intron has a length of about 0.5 kb and splits the codon for tryptophan(314). This genomic organization results in exon 1 encoding the signal peptide, the amino-terminal cysteine-rich region, and the first 9 leucine-rich repeats; exon 2 encoding the last 2 leucine-rich repeats and part of the carboxy-terminal cysteine-rich region; and exon 3 encoding the remainder of the carboxy-terminal cysteine-rich region. The gene does not possess a TATA box prior to its transcription start site. Isolation of a cosmid clone spanning the chondroadherin gene enabled its chromosome location to be established. The gene was shown to reside at chromosome 17q21.33.

Amino Acid Sequence↗
PubMed1997

A high-resolution PAC and BAC map of the SCA2 region.

The spinocerebellar ataxia type 2 (SCA2) gene has been localized to chromosome 12q24.1. To characterize this region and to aid in the identification of the SCA2 gene, we have constructed a 3.9-Mb physical map, which covers markers D12S1328 and D12S1329 known to flank the gene. The map comprises a contig of 84 overlapping yeast artificial chromosomes (YACs), P1 artificial chromosomes (PACs), and bacterial artificial chromosomes (BACs) onto which we placed 82 PCR markers. We localized eight genes and expressed sequence tags on this map, many of which had not been precisely mapped before. In contrast to YACs, which showed a high degree of chimerism and deletions in this region, PACs and BACs were stable. Only 1 in 65 PACs contained a small deletion, and 2 in 18 BACs were chimeric. The high-resolution physical map, which was used in the identification of the SCA2 gene, will be useful for the positional cloning of other disease genes mapped to this region.

Ataxins↗
PubMed1997

Molecular characterization of human neogenin, a DCC-related protein, and the mapping of its gene (NEO1) to chromosomal position 15q22.3-q23.

Neogenin was first identified in the chick embryo, and like a number of cell surface proteins of the immunoglobulin (Ig) superfamily, including N-CAM and L1 (generally called cell adhesion molecules or CAMs), it is expressed on growing nerve cells in the developing nervous system of vertebrate embryos. Neogenin is also expressed in other embryonic tissues, suggesting a more general role in developmental processes such as tissue growth regulation, cell-cell recognition, and cell migration. Neogenin, unlike the CAMs, is closely related to a unique tumor suppressor candidate molecule, deleted in colorectal carcinoma (DCC). Like DCC, the neogenin protein consists of four immunoglobulin-like (Ig-like) domains followed by six fibronectin type III domains, a transmembrane domain, and an intracellular domain. We now report the cloning and sequencing of cDNA clones coding for the human neogenin protein. Human neogenin shares 87% identity with its chicken homolog, and like its chicken counterpart it is expressed in at least two different isoforms derived from alternative splicing in the intracellular domain. Northern blot analysis revealed two mRNA species of about 5 and 7 kb. The chromosomal location of the human neogenin gene (HGMW-approved symbol NEO1) was determined as 15q22.3-q23, using fluorescence in situ hybridization. The gene therefore maps in the vicinity of a locus associated with Bardet-Biedl syndrome. The identification of human neogenin and its chromosomal location provides a basis for studying its involvement in genetic disorders or diseases.

Alternative Splicing↗
PubMed1997

BAC and PAC contigs covering 3.5 Mb of the Down syndrome congenital heart disease region between D21S55 and MX1 on chromosome 21.

Chromosome 21 is a model for the study of human chromosomal aneuploidy, and the construction of its physical and transcriptional maps is a necessary step in understanding the molecular basis of aneuploidy-dependent phenotypes. To identify the gene(s) responsible for Down syndrome congenital heart disease (DS-CHD), we constructed a physical map of the D21S55 to MX1 region. A bacterial artificial chromosome (BAC) library was screened using several YACs spanning the interval, and a P1-derived artificial chromosome (PAC) library was screened using radiolabeled STS PCR products and whole BACs in gap-filling initiatives. FISH confirmed the location of all BAC and PAC clones to 21q22.2-q22.3. Overlaps were established using clone-to-clone Southerns and 24 new STSs, generated from the direct sequencing of BAC and PAC ends, along with 35 preexisting STSs. Approximately 3.5 Mb of the 4- to 5-Mb D21S55 to MX1 interval is covered in 85 BACs and 24 PACs, representing fourfold coverage within the contigs. These BAC and PAC contigs are valuable reagents for isolating the genes for DS-CHD.

Base Sequence↗
PubMed1997

Experimental study of double-lumen, two-stage endotracheal tube during conventional mechanical ventilation in rabbits.

OBJECTIVE: To evaluate the effects of a double-lumen, two-stage endotracheal tube on gas exchanges (ventilatory efficiency) during conventional mechanical ventilation, using a ventilator in rabbits. DESIGN: Prospective, randomized, crossover laboratory animal trial. SETTING: Research laboratory in the Beijing Children's Hospital. SUBJECTS: Five adult New Zealand rabbits, weighing 3.2 to 3.7 kg. INTERVENTIONS: A new type of endotracheal tube-the double-lumen two-stage endotracheal tube-was designed and tested for ventilation efficiency in rabbits with normal and injured lungs. The new tube (size 3.0 mm) was made out of two Portex endotracheal tubes (size 3.0 mm) by adhering two vertical cross-sections at the distal end of the two tubes. The new tube and a conventional endotracheal tube of the same size (inner diameter 3.0 mm) were randomly used in pressure control ventilation. Each trial was maintained for 30 mins. MEASUREMENTS AND MAIN RESULTS: Effects from the two endotracheal tubes on pulmonary mechanics, hemodynamics, and gas exchange were observed. We measured peak inspiratory pressure, positive end-expiratory pressure (PEEP), intrinsic PEEP, mean airway pressure, and arterial blood and mixed expired gas variables (Pao2, Paco2, pH, and mixed expired gas Pco2). The new endotracheal tube acutely increased CO2 elimination in all animals with normal and injured lungs. Paco2 decreased from 46 +/- 4 to 36 +/- 5 torr (6.1 +/- 0.5 to 4.8 +/- 0.7 kPa; p < .01) in normal lungs and from 48 +/- 5 to 36 +/- 5 (6.4 +/- 0.7 to 4.8 +/- 0.7 kPa; p < .01). Meanwhile, tidal volume fraction decreased from 0.48 +/- 0.07 to 0.35 +/- 0.05 (p < .01) and from 0.56 +/- 0.07 to 0.40 +/- 0.07 (p < .01) in normal and injured lungs, respectively. Intrinsic PEEP of the new tube slightly increased, but there were no significant differences in comparison with the conventional tube. CONCLUSION: Compared with the conventional endotracheal tube, the new double-lumen, two-stage endotracheal tube reduced Paco2 by decreasing anatomical deadspace in rabbits with normal and injured lungs under pressure control ventilation, thus enhancing ventilatory efficiency and reducing ventilator-induced injury.

Animals↗
PubMed1997

Cloning, characterization, and copy number of the murine survival motor neuron gene: homolog of the spinal muscular atrophy-determining gene.

Because of a 500-kb inverted duplication, there are two copies of the survival motor neuron (SMN) gene in humans, cenSMN and telSMN. Both genes produce identical ubiquitously expressed transcripts; however, only mutations in telSMN are responsible for spinal muscular atrophy (SMA), the second most common autosomal recessive childhood disease. We have cloned the murine homolog Smn and mapped the gene to Chromosome 13 within the conserved syntenic region of human chromosome 5q13. We show that the Smn transcript (1.4 kb) is expressed as early as embryonic day 7. In contrast to humans, we found no evidence of alternative splicing. The predicted amino acid sequence between mouse and human SMN is 82% identical, and a putative nuclear localization signal is conserved. FISH data indicate that the duplication of the SMA region observed in humans is not present in the mouse. We also found no evidence of multiple Smn genes using Southern blot hybridization and single-strand conformation analysis. Using these methods, we detected at least four copies of Naip exon 5 clustering distal to Smn. Finally, three biallelic markers were identified within the Smn coding region; two are silent polymorphisms, whereas the third changes a cysteine residue to a tyrosine residue in exon 7. Overall, our results indicate that Smn is single copy within the mouse genome, which should facilitate gene disruption experiments to create an animal model of SMA.

Amino Acid Sequence↗
PubMed1996

The gene organization, chromosome location, and expression of a 55-kDa matrix protein (PRELP) of human articular cartilage.

The gene corresponding to a 55-kDa matrix protein previously described in adult human articular cartilage was characterized by sequencing of genomic clones. The deduced protein sequence corresponds to the recently described matrix protein PRELP. The protein was encoded by messages of 1.7, 4.6, and 6.7 kb, whose relative abundance increased as their size decreased. The message heterogeneity appears to originate from variation in the length of the 3'-untranslated region, with the smallest message being contained within the reported sequence and the larger messages having extended 3'-untranslated regions. Two introns were identified within the genomic sequence encoding the smallest message. The first intron of about 6.7 kb resides 16 nucleotides prior to the translation initiation codon, and the second intron of about 2.6 kb resides 173 nucleotides prior to the translation termination codon. The gene, which encompasses at least 16 kb of genomic DNA, was shown to reside on chromosome 1q32. Primer extension techniques were used to establish that the coding sequence commences 199 bp downstream from the major transcription start site. Analysis of the DNA sequence upstream from the transcription start site reveals the presence of numerous potential transcription factor binding sites, but no CAAT or TATA box. At the message level, gene expression was at a high level in juvenile and adult cartilage, but not in the fetus or neonate. The presence of protein in the cartilage matrix was also much lower in the neonate than in the adult. In noncartilagenous tissues appreciable message levels were observed only in the adult lung.

Adult↗
PubMed1996

Characterization of a highly conserved human homolog to the chicken neural cell surface protein Bravo/Nr-CAM that maps to chromosome band 7q31.

The neuronal cell adhesion molecule Bravo/Nr-CAM is a cell surface protein of the immunoglobulin (Ig) superfamily and is closely related to the L1/NgCAM and neurofascin molecules, all of which contain six immunoglobulin domains, five fibronectin repeats, a transmembrane region, and an intracellular domain. Chicken Bravo/Nr-CAM has been shown to interact with other cell surface molecules of the Ig superfamily and has been implicated in specific pathfinding roles of axonal growth cones in the developing nervous system. We now report the characterization of cDNA clones encoding the human Bravo/Nr-CAM protein, which, like its chicken homolog, is composed of six V-like Ig domains and five fibronectin type III repeats. The human Bravo/Nr-CAM homolog also contains a transmembrane and intracellular domain, both of which are 100% conserved at the amino acid level compared to its chicken homolog. Overall, the human Bravo/Nr-CAM homolog is 82% identical to the chicken Bravo/Nr-CAM amino acid sequence. Independent cDNAs encoding four different isoforms were also identified, all of which contain alternatively spliced variants around the fifth fibronectin type III repeat, including one isoform that had been previously identified for chicken Bravo/Nr-CAM. Northern blot analysis reveals one mRNA species of approximately 7.0 kb in adult human brain tissue. Fluorescence in situ hybridization maps the gene for human Bravo/Nr-CAM to human chromosome 7q31.1-q31.2. This chromosomal locus has been previously identified as containing a tumor suppressor candidate gene commonly deleted in certain human cancer tissues.

Amino Acid Sequence↗
PubMed1996

Identification and analysis of the human and murine putative chromatin structure regulator SUPT6H and Supt6h.

We have isolated and sequenced SUPT6H and Supt6h, the human and murine homologues of the Saccharomyces cerevisiae and Caenorhabditis elegans genes SPT6 (P using 1603 aa = 6.7 e-95) and emb-5 (P using 1603 aa = 7.0 e-288), respectively. The human and murine SPT6 homologues are virtually identical, as they share >98% identity and >99% similarity at the protein level. The derived amino acid sequences of these two genes predict a 1603-aa protein (human) and a 1726-bp protein (mouse), respectively. There were several known features, including a highly acidic 5'-region, a degenerate SH2 domain, and a leucine zipper. These features are consistent with a nuclear protein that regulates transcription, whose extreme conservation underscores the likely importance of this gene in mammalian development. Expression of human and murine SPT6 homologues was analyzed by Northern blotting, which revealed a 7. 0-kb transcript that was expressed constitutively. The SPT6 homologue was mapped to chromosome 17q11.2 in human by somatic cell hybrid analysis and in situ hybridization. These data indicate that SUPT6H and Supt6h are functionally analogous to SPT6 and emb-5 and may therefore regulate transcription through establishment or maintenance of chromatin structure.

Amino Acid Sequence↗
PubMed1996

Chromosomal localization of murine and human oligodendrocyte-specific protein genes.

Oligodendrocyte-specific protein (OSP) is a recently described protein present only in myelin of the central nervous system. Several inherited disorders of myelin are caused by mutations in myelin genes but the etiology of many remain unknown. We mapped the location of the mouse OSP gene to the proximal region of chromosome 3 using two sets of multilocus crosses and to human chromosome 3 using somatic cell hybrids. Fine mapping with fluorescence in situ hybridization placed the OSP gene at human chromosome 3q26.2-q26.3. To date, there are no known inherited neurological disorders that localize to these regions.

Animals↗
PubMed1996

APP-BP1, a novel protein that binds to the carboxyl-terminal region of the amyloid precursor protein.

beta-Amyloid protein precursors (APPs, 695-770 amino acids) are the source of the 39-43 amino acid beta-amyloid (A beta) peptides that comprise diffuse and fibrillar deposits in the cerebral cortex and vasculature of Alzheimer's disease brains. A beta is thought to play a role in the pathogenesis of Alzheimer's disease, and, hence, considerable effort has been invested in defining the means by which A beta is generated from the APPs. Knowledge of the normal function of the APPs is sure to provide insights into the genesis and pathological persistence of A beta in Alzheimer's disease. APP is a cell surface protein with a large extracellular amino-terminal domain, a single transmembrane segment, and a short cytoplasmic tail. Its location and structural features characteristic of a receptor for signal transduction led us to search for potential effector proteins capable of binding and interacting with its cytoplasmic domain. Here, we report the cloning of a cDNA encoding one such protein. This ubiquitously expressed 59-kDa APP-binding protein, called APP-BP1, is 61% similar to a protein encoded by the Arabidopsis AXR1 gene, required for normal response to the hormone auxin, and is a relative of the ubiquitin activating enzyme E1.

Adult↗
PubMed1996

Specific cloning of human DNA as yeast artificial chromosomes by transformation-associated recombination.

DNA molecules undergoing transformation into yeast are highly recombinogenic, even when diverged. We reasoned that transformation-associated recombination (TAR) could be employed to clone large DNAs containing repeat sequences, thereby eliminating the need for in vitro enzymatic reactions such as restriction and ligation and reducing the amount of DNA handling. Gently isolated human DNA was transformed directly into yeast spheroplasts along with two genetically marked (M1 and M2) linearized vectors that contained a human Alu sequence at one end and a telomere sequence at the other end (Alu-CEN-M1-TEL and Alu-M2-TEL). Nearly all the M1-selected transformants had yeast artificial chromosomes (YACs) containing human DNA inserts that varied in size from 70 kb to > 600 kb. Approximately half of these had also acquired the unselected M2 marker. The mitotic segregational stability of YACs generated from one (M1) or two (M1 and M2) vector(s) was comparable, suggesting de novo generation of telomeric ends. Since no YACs were isolated when rodent DNAs or a vector lacking an Alu sequence was used, the YACs were most likely the consequence of TAR between the repeat elements on the vector(s) and the human DNA. Using the BLUR13 Alu-containing vector, we demonstrated that human DNA could be efficiently cloned from mouse cells that contained a single human chromosome 16. The distribution of cloned DNAs on chromosome 16 was determined by fluorescence in situ hybridization. We propose that TAR cloning can provide an efficient means for generating YACs from specific chromosomes and subchromosome fragments and that TAR cloning may be useful for isolating families of genes and specific genes from total genome DNA.

Animals↗
PubMed1996

Localization of the human RGR opsin gene to chromosome 10q23.

The human RGR gene encodes an opsin protein (retinal G protein-coupled receptor), which is expressed in Müller cells and the retinal pigment epithelium and is thought to play a role in the visual process. To investigate a possible linkage of the RGR gene to retinal dystrophies, the locus of the gene was mapped on human metaphase chromosomes. Genomic and cDNA fragments of the human RGR gene were used as probes for fluorescence in situ hybridization. Analysis of the fluorescence signals on high-resolution banded chromosomes showed that the RGR gene is localized to human chromosome 10q23. This result now provides for the rapid analysis of this gene with respect to inherited diseases of the retina.

Chromosome Banding↗
PubMed1996

Moderate expansion of a normally biallelic trinucleotide repeat in spinocerebellar ataxia type 2.

The gene for spinocerebellar ataxia type 2 (SCA2) has been mapped to 12q24.1. A 1.1-megabase contig in the candidate region was assembled in P1 artificial chromosome and bacterial artificial chromosome clones. Using this contig, we identified a CAG trinucleotide repeat with CAA interruptions that was expanded in patients with SCA2. In contrast to other unstable trinucleotide repeats, this CAG repeat was not highly polymorphic in normal individuals. In SCA2 patients, the repeat was perfect and expanded to 36-52 repeats. The most common disease allele contained (CAG)37, one of the shortest expansions seen in a CAG expansion syndrome. The repeat occurs in the 5'-coding region of SCA2 which is a member of a novel gene family.

Amino Acid Sequence↗
PubMed1995

Localization of the tight junction protein gene TJP1 to human chromosome 15q13, distal to the Prader-Willi/Angelman region, and to mouse chromosome 7.

The gene encoding the tight junction (zonula occludens) protein, TJP1, was mapped to human chromosome 15q13 by fluorescence in situ hybridization (FISH) using a cDNA probe. The Jackson Laboratory backcross DNA panel derived from the cross (C57BL/6JEi x SPRET/Ei) F1 females x SPRET/Ei males was used to map the mouse Tjp1 to chromosome 7 near position 30 on the Chromosome Committee Map, a region with conserved homology to human chromosome 15q13. FISH studies on metaphases from patients with the Prader-Willi (PWS) or the Angelman syndrome (AS) showed that TJP1 maps close but distal to the PWS/AS chromosome region.

Angelman Syndrome↗