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Biomedical subjects

J X Jiang

Publications and source records attributed to J X Jiang.

At least 19 recordsLinked to original sources
PubMed2005

Delimitation of the rice wide compatibility gene S5 ( n ) to a 40-kb DNA fragment.

Wide compatibility varieties (WCVs) are a special class of rice (Oryza sativa L.) germplasm that produces hybrids with normal pollen and spikelet fertility when crossed with both indica and japonica subspecies. The wide compatibility gene S5 ( n ) has been used extensively in inter-subspecific hybrid breeding programs. We previously mapped the S5 locus to a 2.2-cM genomic region between RM253 and R2349 on chromosome 6, using a population of 356 F(1) plants derived from the three-way cross 02428/Nanjing11//Balilla. In this study, a chromosome walking strategy was employed to construct a physical map covering this genomic region using these two closest markers as the starting points. A physical map consisting of six overlapping BAC clones was formed, spanning a genomic region of 540-kb in length. By analyzing recombination events from a population of 8,000 F(1) plants derived from a three-way cross based on near isogenic lines of the S5 locus, the S5 locus was localized to a DNA fragment of 40-kb in length, flanked by two shotgun subclones, 7B1 and 15D2. Sequence analysis of this fragment predicted five open reading frames, encoding xyloglucan fucosyltransferases, dnak-type molecular chaperone BiP, a putative eukaryotic aspartyl protease, and a hypothetical protein. This result will be very useful in molecular cloning of the S5 ( n ) allele and marker-assisted transferring of the wide compatibility gene in rice breeding programs.

Aspartic Acid Endopeptidases↗
PubMed2005

A two year family based behaviour treatment for obese children.

BACKGROUND: Childhood obesity has become a nutritional problem in China since the 1990s. AIMS: A family based behavioural treatment was developed and tested, to see if its use was feasible in China and to evaluate its impact on obese schoolchildren. METHODS: In a single school in Beijing, 33 obese children were randomly assigned to a treatment group and 35 to a control group. The treatment group participated in a family based behavioural treatment programme for two years. Height and weight were measured every six months for all participants. Blood pressure, cholesterol, and triglyceride levels were measured at baseline and after two years of programme implementation. RESULTS: Body mass index (BMI, kg/m2) was significantly reduced in the treatment group (from 26.6 (1.7) to 24.0 (0.9), 95% CI 2.06 to 3.18) but not in the control group (from 26.1 (1.5) to 26.0 (1.6)). Total cholesterol decreased 5.5% and triglycerides 9.7% in the treatment group. There was a significant correlation between change in BMI and change in triglycerides. There were no significant changes in plasma lipids in the controls. Blood pressure values also decreased significantly in the treatment, but not the control group. CONCLUSIONS: A family based behavioural intervention was feasible to use in treating obesity in schoolchildren in Beijing, China. After two years of implementation, it successfully decreased the degree of obesity, reduced levels of blood pressure, and decreased serum lipids in treatment; there were no significant changes among control children.

Adolescent↗
PubMed2005

Chiral ligands derived from Abrine 8. An experimental and theoretical study of free ligand conformational preferences and the addition of diethylzinc to benzaldehyde.

Three structurally similar series of 1,2,3,4-tetrahydro-beta-carboline ligands, 4a-d, 6a-d and 7a-d, and two series of chiral oxazolidines, 8a-d and 9a-g, were synthesized and used as chiral catalysts in the addition of diethylzinc to benzaldehyde. The enantioselectivities of the resulting 1-phenyl-1-propanol were obtained in each case, and these ee values were, in most cases, related to the conformational populations of the free ligand as expressed by the calculated differences in the energies of the ligand conformations formed by inversion at nitrogen. This suggested the possible existence of a linear free energy relationship. The effect on enantioselectivity of the carbon chain length of the R group located (1) on the C-3 substituent of 4a-d, 6a-d, and 7a-d or (2) at C-5 in 8a-d and 9a-g was studied in detail. On the basis of the correlations observed and the ligands' structural characterization, a structure was proposed for the transition state during ethyl group transfer when using ligands 8a-d. Furthermore, the change in enantioselectivity was successfully predicted when diastereomeric ligands 11 and 12 were compared in this chiral addition.

Benzaldehydes↗
PubMed2002

Maize dwarf mosaic disease in different regions of China is caused by Sugarcane mosaic virus.

Sugarcane mosaic virus (SCMV) was detected in all 62 maize samples collected from eight maize-growing provinces in China showing dwarf mosaic symptoms by immunocapture reverse-transcription polymerase chain reaction (RT-PCR). Maize dwarf mosaic virus (MDMV), Sorghum mosaic virus (SrMV) and Johnsongrass mosaic virus (JGMV), however, were not detected in any of the samples by RT-PCR. Eleven cDNA fragments of approximately 0.8 kilobases covering most of the coat protein (CP) gene of SCMV were sequenced and sequence analysis indicates that these eleven isolates share 98.1 to 100 % identity at the amino acid level. Sequence comparison and phylogenetic analysis of the CP genes from the eleven Chinese isolates as well as 21 SCMV subgroup virus isolates indicate that the eleven Chinese virus isolates were closely related to SCMV with 97.0 to 98.1 % sequence identity at the amino acid level, while relatively lower sequence identity was found with MDWV, SrMV or JGMV. The results indicate that the Chinese isolates are members of the SCMV species, and thus, SCMV can be considered as the most common and important potyvirus infecting maize in China.

Amino Acid Sequence↗
PubMed2001

The development-associated cleavage of lens connexin 45.6 by caspase-3-like protease is regulated by casein kinase II-mediated phosphorylation.

Gap junctions are important in maintaining lens transparency and metabolic homeostasis. In this paper, we report that the gap junction-forming protein, connexin (Cx) 45.6, was specifically truncated during lens development and that the majority of the truncated fragments were located in the differentiated lens fibers. When isolated lens membranes were treated by caspase-3, the truncated fragments of Cx45.6 were reproduced, and this truncation occurred at the COOH terminus of Cx45.6. Moreover, when primary lens cells were treated with apoptosis-inducing reagents, Cx45.6 was cleaved similarly as the in vitro treatment by caspase-3, and this cleavage was blocked by a caspase-3 inhibitor. These results suggest that caspase-3 is responsible for the development-associated cleavage of Cx45.6. The cleavage site of Cx45.6 was identified between amino acid residues Glu(367) and Gly(368). We have shown previously that Ser(363) is an in vivo phosphorylated site by casein kinase II, and this specific phosphorylation leads to a rapid turnover of Cx45.6. Interestingly, we found here that when Ser(363) was phosphorylated by casein kinase II, the cleavage of Cx45.6 catalyzed by caspase-3 was inhibited. This study, for the first time, demonstrates that a connexin can be a direct target of an apoptotic protease and that cleavage by caspase-3-like protease leads to the development-associated truncation of a lens connexin. Finally, caspase-3-mediated cleavage can be regulated by casein kinase II-mediated phosphorylation, suggesting that Cx45.6 turnover and specific cleavage by caspase-3-like protease is alternatively modulated.

Animals↗
PubMed2001

A novel human amino acid transporter, hNAT3: cDNA cloning, chromosomal mapping, genomic structure, expression, and functional characterization.

Amino acid transporters are proteins that transport amino acids across the membrane. We report here the isolation and characterization of a novel human cDNA clone encoding a protein of 547 amino acids. This protein shares approximately 50% amino acid sequence homology with the amino acid transporters mouse mNAT and its orthologs, rat SN1 and human g17, and mouse GlnT/ATA1 and ATA2. Expression of this cRNA in Xenopus oocytes revealed that the strongest transport activities were specific for l-alanine. In addition, hNAT3 is a Na(+)- and pH-dependent, low-affinity transporter and partially tolerates substitution of Na(+) by Li(+). Since this protein has sequence and functional similarities to the previously identified system N amino acid transporters, we named this protein hNAT3. The genomic DNA sequence encoding the transcript of hNAT3 spans over 14 kb with 16 exons and 15 introns. Using fluorescence in situ hybridization, we mapped the hNAT3 gene to human chromosome 12q12-q13. By RT-PCR of embryonic and adult human tissues, hNAT3 was detected to be predominantly expressed in the liver and to a much lesser extent in the muscle, kidney, and pancreas. The data obtained in this study are likely to offer critical clues for identification of amino acid transporter-associated diseases.

Alanine↗
PubMed2001

Characterization of an N-system amino acid transporter expressed in retina and its involvement in glutamine transport.

We report here on the characterization of a mouse N-system amino acid transporter protein, which is involved in the transport of glutamine. This protein of 485 amino acids shares 52% sequence homology with an N-system amino acid transporter, mouse N-system amino acid transporter (mNAT) and its orthologs. Because this protein shares a high degree of sequence homology and functional similarity to mNAT, we named it mNAT2. mNAT2 is predominately expressed in the retina and to a slightly lesser extent in the brain. In the retina, it is located in the axons of ganglion cells in the nerve fiber layer and in the bundles of the optic nerve. Functional analysis of mNAT2 expressed in Xenopus oocytes revealed that the strongest transport activities were specific for l-glutamine. In addition, mNAT2 is a Na(+)- and pH-dependent, high affinity transporter and partially tolerates substitution of Na(+) by Li(+). Additionally, mNAT2 functions as a carrier-mediated transporter that facilitates efflux. The unique expression pattern and selective glutamine transport properties of mNAT2 suggest that it plays a specific role in the uptake of glutamine involved in the generation of the neurotransmitter glutamate in retina.

Acetyltransferases↗
PubMed2001

PGE(2) is essential for gap junction-mediated intercellular communication between osteocyte-like MLO-Y4 cells in response to mechanical strain.

We have observed, in our previous studies, that fluid flow increases gap junction-mediated intercellular coupling and the expression of a gap junction protein, connexin 43, in osteocyte-like MLO-Y4 cells. Interestingly, this stimulation is further enhanced during the poststress period, indicating that a released factor(s) is likely to be involved. Here, we report that the conditioned medium obtained from the fluid flow-treated MLO-Y4 cells increased the number of functional gap junctions and connexin 43 protein. These changes are similar to those observed in MLO-Y4 cells directly exposed to fluid flow. Fluid flow was found to induce PGE(2) release and increase cyclooxygenase 2 expression. Treatment of the cells with PGE(2) had the same effect as fluid flow, suggesting that PGE(2) could be responsible for these autocrine effects. When PGE(2) was depleted from the fluid flow-conditioned medium, the stimulatory effect on gap junctions was partially, but significantly, decreased. Addition of the cyclooxygenase inhibitor, indomethacin, partially blocked the stimulatory effects of mechanical strain on gap junctions. Taken together, these studies suggest that the stimulatory effect of fluid flow on gap junctions is mediated, in part, by the release of PGE(2). Hence, PGE(2) is an essential mediator between mechanical strain and gap junctions in osteocyte-like cells.

Animals↗
PubMed2001

Expression of functional gap junctions and regulation by fluid flow in osteocyte-like MLO-Y4 cells.

Osteocytes are thought to be mechanosensory cells that respond to mechanical stress by sending signals to other bone cells to initiate bone remodeling. An osteocyte-like cell line MLO-Y4 provides a model system to examine whether gap junctions participate in the regulation of osteocyte function and signaling by mechanical stress. In this study, we show that MLO-Y4 cells are coupled and that gap junction channels mediate this coupling. Biochemical analyses show that connexin 43 (Cx43) is a major gap junction protein expressed in MLO-Y4 cells and approximately 5% of Cx43 protein is phosphorylated. MLO-Y4 cells were exposed to mechanical stress using a parallel plate flow chamber to model bone fluid flow shear stress. Fluid flow increased significantly the length of the dendritic processes, a morphological characteristic of osteocytes. A redistribution of the gap junction protein, Cx43 also was observed from a location circling the nucleus to punctate spots in the cytoplasm and in the dendritic processes. "Scrape-loading" dye transfer analyses showed that fluid flow increased intercellular coupling and increased the number of cells coupled immediately after fluid flow treatment, in direct proportion to shear stress magnitude. Although intercellular coupling continued to increase, stimulation of Cx43 protein expression during the poststress period was found to be biphasic. Cx43 protein was elevated 30 minutes after application of stress but decreased at 24 h poststress. Pulsating fluid flow had a similar stimulatory effect as steady fluid flow on gap junctions. However, this stimulatory effect in osteocyte-like cells was not observed in osteoblast-like 2T3 cells. Together, these results show that fluid flow has stimulatory effects on osteocyte-like MLO-Y4 cells with early effects on cellular morphology, opening of gap junctions, and redistribution of Cx43 protein and delayed effects on Cx43 protein expression. The high expression of Cx43 and its location in the cytoplasm also suggest that Cx43 may have unknown functions in addition to forming gap junctions. These studies indicate that gap junctions may serve as channels for signals generated by osteocytes in response to mechanical loading.

Blotting, Western↗
PubMed2001

Mechanical stimulation of gap junctions in bone osteocytes is mediated by prostaglandin E2.

Gap junction-mediated intercellular communications are thought to transduce the effects of mechanical strain from osteocytes to cells on the bone surface to initiate remodeling. To determine whether gap junctions may co-ordinate the effects of mechanical loading, osteocyte-like MLO-Y4 cells were exposed to fluid flow-imposed shear stress. After exposure of MLO-Y4 to fluid flow, intercellular coupling increased in direct proportion to shear stress level. Interestingly, this stimulation is further enhanced during the post-stress period, indicating that released factor(s) is likely to be involved. The conditioned medium obtained from the fluid flow treated MLO-Y4 cells induced an increase in the number of functional gap junctions and Cx43 protein when added to non-sheer-stressed cells. Fluid flow was found to induce prostaglandin F2 (PGE2) release and increase cyclooxygenase 2 (COX-2) expression. When PGE2 was depleted from the fluid flow conditioned medium, the stimulatory effect on gap junctions was significantly decreased. Addition of the COX inhibitor indomethacin partially blocked the stimulatory effects of mechanical strain on gap junctions. Together, these studies suggest that the stimulatory effect of fluid flow on gap junctions is mediated in part by de novo synthesis and release of PGE2. Gap junctions may serve as channels for the signals generated by osteocytes in response to mechanical loading.

Animals↗
PubMed2001

Regulation of lens connexin 45.6 by apoptotic protease, caspase-3.

Gap junctions are important in maintaining lens homeostasis. Here we report that connexin 45.6 (Cx45.6) was partially truncated to a 46 kDa fragment during chicken lens development. This specific truncation initiated during embryonic days and the truncated fragment accumulated towards the later developmental stages. When membranes of the embryonic lens were subjected to caspase-3 treatment, the 46 kDa fragment of Cx45.6 was reproduced, suggesting apoptotic protease caspase-3 is a potential protease involved. The COOH-terminus of Cx45.6 in GST-fusion protein was also cleaved by caspase-3, confirming that Cx45.6 is a direct substrate of caspase-3. Induction of apoptosis in lens primary cultures regenerated the 46 kDa fragment and this cleavage was blocked by a caspase-3 inhibitor. Alteration of amino acid residue Asp364 or Glu367 to Ala prevented Cx45.6 from cleavage by caspase-3, suggesting that the cleavage site of Cx45.6 is likely to be between Glu367 and Gly361. Phosphorylation of Ser363, a known substrate for casein kinase II (CKII) in vivo, inhibited the cleavage of Cx45.6 by caspase-3. Thus, this study demonstrates that a lens connexin can be a direct target of caspase-3 and the cleavage by caspase-3 leads to the development-associated truncation of Cx45.6. Finally, caspase-3 mediated truncation can be modulated by the specific connexin phosphorylation.

Animals↗
PubMed2001

Cloning a novel mouse Gabarapl2 cDNA and its characterization.

AIM: To clone a novel mouse GABAA-receptor-associated protein like 2 (Gabarapl2) gene, and to analysis its primary function. METHODS: With the aid of computer, the human GABARAPL2 cDNA was used as information probe to search mouse EST database of GenBank for mouse homolog. A series of overlapping EST were found and assembled into an EST contig using Genetics Computer Group (GCG) ASSEMBLY program. The existence of the gene was then identified by experiment. Northern blotting was performed to hybridize [alpha-32P]dATP labeled probe with mRNA of 11 different mouse tissues that had been transferred to the nylon membrane. RESULTS: The novel gene was deposited in GenBank under Accession No AF190644. Its cDNA contained an intact open reading frame and a canonical polyadenylation signal AATAAA followed by polyA. The deduced protein was completely identical to that of human GABARAPL2, and was termed Gabarapl2 by Mouse Gene Nomenclature Committee. The putative protein of Gabarapl2 has a calculated molecular weight of 13 700 and an isoelectric point of 8.56. It was also predicted to contain two protein kinase C phosphorylation sites and one tyrosine kinase phosphorylation site. Northern hybridization showed that Gabarapl2 was expressed as a single 1.35 kb transcript, with high levels in brain, thymus, lung, heart, kidney, and liver, and low in pancreas, testis, small intestine, colon, and stomach. CONCLUSION: A novel mouse Gabarapl2 gene was cloned and identified.

Adaptor Proteins, Signal Transducing↗
PubMed2000

Identification and characterization of an amino acid transporter expressed differentially in liver.

Cellular metabolic needs are fulfilled by transport of amino acids across the plasma membrane by means of specialized transporter proteins. Although many of the classical amino acid transporters have been characterized functionally, less than half of these proteins have been cloned. In this report, we identify and characterize a cDNA encoding a plasma membrane amino acid transporter. The deduced amino acid sequence is 505 residues and is highly hydrophobic with the likely predicted structure of 9 transmembrane domains, which putatively place the amino terminus in the cytoplasm and the carboxy terminus on the cell surface. Expression of the cRNA in Xenopus laevis oocytes revealed strong transport activities specific for histidine and glutamine. This protein is a Na(+)- and pH-dependent transporter and tolerates substitution of Na(+) by Li(+). Furthermore, this transporter is not an obligatory exchanger because efflux occurs in the absence of influx. This transporter is expressed predominantly in the liver, although it is also present in the kidney, brain, and heart. In the liver, it is located in the plasma membrane of hepatocytes, and the strongest expression was detected in those adjacent to the central vein, gradually decreasing towards the portal tract. Because this protein displays functional similarities to the N-system amino acid transport, we have termed it mNAT, for murine N-system amino acid transporter. This is the first transporter gene identified within the N-system, one of the major amino acid transport systems in the body. The expression pattern displayed by mNAT suggests a potential role in hepatocyte physiology.

Amino Acid Sequence↗
PubMed2000

Casein kinase II phosphorylates lens connexin 45.6 and is involved in its degradation.

Connexin (Cx) 45.6, an avian counterpart of rodent Cx50, is phosphorylated in vivo, but the sites and function of the phosphorylation have not been elucidated. Our peptide mapping experiments showed that the Ser(363) site in the carboxyl (COOH) terminus of Cx45.6 was phosphorylated and that this site is within casein kinase (CK) II consensus sequence, although showing some similarity to CKI sequence. The peptide containing Ser(363) could be phosphorylated in vitro by CKII, but not by CKI. Furthermore, CKII phosphorylated Cx45.6 in embryonic lens membrane and the fusion protein containing the COOH terminus of Cx45.6. Two-dimensional peptide mapping experiments showed that one of the Cx45.6 peptides phosphorylated in vivo migrated to the same spot as one of those phosphorylated by CKII in vitro. Furthermore, CKII activity could be detected in lens lysates. To assess the function of this phosphorylation event, exogenous wild type and mutant Cx45.6 (Ser(363) --> Ala) were expressed in lens primary cultures by retroviral infection. The mutant Cx45.6 was shown to be more stable having a longer half-life compared with wild type Cx45.6. Together, the evidence suggests that CKII is likely a kinase responsible for the Ser(363) phosphorylation, leading to the destablization and degradation of Cx45.6. The connexin degradation induced by phosphorylation has a broad functional significance in the regulation of gap junctions in vivo.

Amino Acid Sequence↗
PubMed1999

Formation of heteromeric gap junction channels by connexins 40 and 43 in vascular smooth muscle cells.

Connexin (Cx) 43 and Cx40 are coexpressed in several tissues, including cardiac atrial and ventricular myocytes and vascular smooth muscle. It has been shown that these Cxs form homomeric/homotypic channels with distinct permeability and gating properties but do not form functional homomeric/heterotypic channels. If these Cxs were to form heteromeric channels, they could display functional properties not well predicted by the homomeric forms. We assessed this possibility by using A7r5 cells, an embryonic rat aortic smooth muscle cell line that coexpresses Cxs 43 and 40. Connexons (hemichannels), which were isolated from these cells by density centrifugation and immunoprecipitated with antibody against Cx43, contained Cx40. Similarly, antibody against Cx40 coimmunoprecipitated Cx43 from the same connexon fraction but only Cx40 from Cx (monomer) fractions. These results indicate that heteromeric connexons are formed by these Cxs in the A7r5 cells. The gap junction channels formed in the A7r5 cells display many unitary conductances distinct from homomeric/homotypic Cx43 or Cx40 channels. Voltage-dependent gating parameters in the A7r5 cells are also quite variable compared with cells that express only Cx40 or Cx43. These data indicate that Cxs 43 and 40 form functional heteromeric channels with unique gating and conductance properties.

Animals↗
PubMed1998

Phosphorylation of lens-fiber connexins in lens organ cultures.

Lens gap junction proteins, connexins [1], are known to be phosphorylated in vivo. Phosphorylated states of connexins were examined in lens cultures to define in vitro models for the study of the functions of lens connexin phosphorylation in lens biology. In organ and differentiated cell primary cultures, chick lens-fiber connexins, connexin45.6 and connexin56, were labeled with [32P]orthophosphate. Pulse-chase experiments of lens organ cultures with [35S]methionine demonstrated that connexin45.6 and connexin56 were properly processed into the phosphorylated forms observed in vivo. However, in lens cell primary cultures, both connexins had short half-lives, and connexin56 was degraded before it was phosphorylated into the form which showed the largest mobility shift. The data suggested that the phosphorylation patterns of connexins in lens organ cultures were similar to in vivo connexin phosphorylation, while primary cultures revealed abnormal rates of protein turnover and incomplete phosphorylation. Treatment of lens organ cultures with protein kinase inhibitors indicated that protein kinase C was involved in the phosphorylation of connexin45.6 and connexin56. Comparison of the phosphopeptide patterns by two-dimensional mapping suggested that protein kinase C was involved in the phosphorylation of connexin45.6 and that it phosphorylated the C-terminus of connexin45.6 in vitro.

Animals↗
PubMed1998

Retroviral expression of connexins in embryonic chick lens.

PURPOSE: To develop an in vivo model system in which exogenous proteins can be expressed in embryonic chick lens and to further understand the function of connexin-mediated gap junction intercellular communication in lens cell biology. METHODS: RCAS(A) is a replication-competent chicken retrovirus that infects dividing cells. Retroviral constructs were prepared containing alkaline phosphatase (AP) and FLAG-tagged connexins. Chick lenses were infected in situ by injecting virus into the lumen of lens vesicles at stage 18, cultures were taken at various periods. The lenses were then dissected, and the expressed proteins were visualized by AP histochemical examination and immunostaining. RESULTS: Twenty-four hours after infection, alkaline phosphatase could be seen in epithelia and fibers. As lens fiber maturation progressed, however, the alkaline phosphatase staining was lost as the fibers matured, presumably because of the proteolytic removal of the enzyme. By 72 hours, alkaline phosphatase staining could still be observed in epithelial cells and in differentiating fibers in the bow region but not in the mature lens fibers. FLAG-tagged exogenous lens connexins were also abundantly expressed by viral infection. The exogenous connexins were localized at the cell surfaces in junctional maculae and showed the same cell-type specific distribution as that of their endogenous connexin counterparts. CONCLUSIONS: An in vivo model system has been developed in the chick that provides opportunities to study the expression of wild-type and mutant proteins during lens differentiation. Expression of wild-type connexins has revealed that the characteristic distribution of the three different lens connexins is maintained even when expression is driven by a viral promoter.

Alkaline Phosphatase↗