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Biomedical subjects

N Lu

Publications and source records attributed to N Lu.

At least 19 recordsLinked to original sources
PubMed2001

A functional role for Tsix transcription in blocking Xist RNA accumulation but not in X-chromosome choice.

In female mammals, up-regulation of Xist triggers X-chromosome inactivation in cis. Up-regulation is inhibited by sequences 3' to Xist contained within the antisense locus, Tsix. Inhibition could depend on transcription of Tsix and/or on DNA elements therein. Here we test the role of Tsix transcription by augmenting the duration and strength of Tsix expression. We find that Tsix hypertranscription is sufficient to block Xist RNA accumulation in a cis-limited manner. We propose that Tsix transcription is necessary to restrict Xist activity on the future active X and, conversely, that Tsix repression is required for Xist RNA accumulation on the future inactive X. We also find that Tsix hypertranscription does not affect X-chromosome choice. Thus, choice is mediated by elements within Tsix that are independent of promoter activity.

Animals↗
PubMed2001

Surprises of genetic engineering: a possible model of polyglucosan body disease.

BACKGROUND: The authors previously reported the generation of a knockout mouse model of Pompe disease caused by the inherited deficiency of lysosomal acid alpha-glucosidase (GAA). The disorder in the knockout mice (GAA-/-) resembles the human disease closely, except that the clinical symptoms develop late relative to the lifespan of the animals. In an attempt to accelerate the course of the disease in the knockouts, the authors increased the level of cytoplasmic glycogen by overexpressing glycogen synthase (GSase) or GlutI glucose transporter. METHODS: GAA-/- mice were crossed to transgenic mice overexpressing GSase or GlutI in skeletal muscle. RESULTS: Both transgenics on a GAA knockout background (GS/GAA-/- and GlutI/GAA-/-) developed a severe muscle wasting disorder with an early age at onset. This finding, however, is not the major focus of the study. Unexpectedly, the mice bearing the GSase transgene, but not those bearing the GlutI transgene, accumulated structurally abnormal polysaccharide (polyglucosan) similar to that observed in patients with Lafora disease, glycogenosis type IV, and glycogenosis type VII. Ultrastructurally, the periodic acid-Schiff (PAS)-positive polysaccharide inclusions were composed of short, amorphous, irregular branching filaments indistinguishable from classic polyglucosan bodies. The authors show here that increased level of GSase in the presence of normal glycogen branching enzyme (GBE) activity leads to polyglucosan accumulation. The authors have further shown that inactivation of lysosomal acid alpha-glucosidase in the knockout mice does not contribute to the process of polyglucosan formation. CONCLUSIONS: An imbalance between GSase and GBE activities is proposed as the mechanism involved in the production of polyglucosan bodies. The authors may have inadvertently created a "muscle polyglucosan disease" by simulating the mechanism for polyglucosan formation.

1,4-alpha-Glucan Branching Enzyme↗
PubMed2001

Identification and characterization of a tissue-specific silencer element in the first intron of the human acid maltase gene.

Deficiency of acid maltase (acid alpha-glucosidase), a lysosomal enzyme that degrades glycogen, results in glycogenosis type II, an autosomal recessive disease whose manifestations and severity largely depend on the level of residual enzyme activity. Previous studies have established that there are transcriptional control elements in the first intron; in particular a silencer responsive to Hes-1 and YY1 has been identified in the human hepatoma line, HepG2. This region functions as an enhancer in human fibroblasts. Here we have localized a silencer active in fibroblasts to a nearby 25-bp element in intron 1. This element repressed thymidine kinase promoter activity by about 50% in both orientations in human fibroblasts. This silencer, as with the previous one, is tissue specific since constructs containing this region are inactive in HepG2 cells. Electrophoretic mobility shift assay revealed three proteins specifically binding to the element in fibroblasts, and site-directed mutagenesis analysis indicated that all the three proteins binding to the element contribute to the silencer function. The data may be helpful for designing therapy to increase the level of enzyme, particularly when, as in most adults with the disease, there is reduced production of structurally normal enzyme.

Chloramphenicol O-Acetyltransferase↗
PubMed2001

[Changes in expression of angiotensin subtype AT1A and AT2 receptors in rats during cardiac remodeling following myocardial infarction].

Immunohistochemical and electron microscopic techniques and image analysis were employed to investigate the regulation of cardiac AT1A and AT2 subtype receptors in rats during cardiac remodeling following myocardial infarction (MI). Positive immunostaining for AT1A and AT2 receptors was observed in myocytes and vessels with AT1A being more than AT2. Three days after MI, disappearance of myocardial cross striation and fibroblast hyperplasia were found with electron microscopy. AT1A receptor protein expression in myocardial noninfarcted portion notably increased compared with that in sham-operated control rats (P < 0.001). No apparent changes were observed in AT2 receptor (P > 0.05). Two weeks after MI, myocyte cross striation and collagen deposition were found. Meanwhile, AT1A receptor staining decreased compared with that of three days after MI (P < 0.01), but there was still more than that of the control (P < 0.05). AT2 receptor was significantly increased compared with that of the sham-operated control rats (P < 0.001). These results suggest that both AT1A and AT2 receptor protein expression was upregulated in noninfarcted myocardium after MI, and the regulation of AT1A and AT2 receptors after MI may be involved in post-infarction cardiac remodeling.

Animals↗
PubMed2000

Transcriptional regulation of the human acid alpha-glucosidase gene. Identification of a repressor element and its transcription factors Hes-1 and YY1.

Acid alpha-glucosidase, the product of a housekeeping gene, is a lysosomal enzyme that degrades glycogen. A deficiency of this enzyme is responsible for a recessively inherited myopathy and cardiomyopathy, glycogenesis type II. We have previously demonstrated that the human acid alpha-glucosidase gene expression is regulated by a silencer within intron 1, which is located in the 5'-untranslated region. In this study, we have used deletion analysis, electrophoretic mobility shift assay, and footprint analysis to further localize the silencer to a 25-base pair element. The repressive effect on the TK promoter was about 50% in both orientations in expression plasmid, and two transcriptional factors were identified with antibodies binding specifically to the element. Mutagenesis and functional analyses of the element demonstrated that the mammalian homologue 1 of Drosophila hairy and Enhancer of split (Hes-1) binding to an E box (CACGCG) and global transcription factor-YY1 binding to its core site function as a transcriptional repressor. Furthermore, the overexpression of Hes-1 significantly enhanced the repressive effect of the silencer element. The data should be helpful in understanding the expression and regulation of the human acid alpha-glucosidase gene as well as other lysosomal enzyme genes.

Base Sequence↗
PubMed2000

Mechanisms of NSAID-induced gastrointestinal injury defined using mutant mice.

BACKGROUND & AIMS: Nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly used agents that have a high incidence of gastrointestinal side effects resulting in significant morbidity and mortality. Leukocytes have been implicated in NSAID-induced injury, but the mechanisms are unclear. We established a murine model of NSAID-induced gastrointestinal damage to assess the roles of candidate gene products in the pathogenesis of this injury. METHODS: Indomethacin-induced gastrointestinal injury was assessed in wild-type and several mutant murine lines. Leukocyte involvement was assessed by neutrophil depletion, impairment of recruitment (resulting from targeted disruption of fucosyltransferase VII [FTVII]), and the absence of mature T and B cells with the use of Rag 2(-/-) mice. Activation and oxygen free radicals were assessed using gp91(phox-/-) mice that exhibit normal leukocyte recruitment but are deficient in myeloid cell activation and oxygen free radical generation. RESULTS: Impairment of leukocyte recruitment (FTVII(/-)) and neutrophil depletion resulted in more than a 50% reduction in NSAID-induced injury. However, mice deficient in mature T and B cells had NSAID-induced damage comparable to control mice. Leukocyte activation was required for NSAID-induced damage because the gp91(phox-/-) mice were less susceptible to NSAID injury than wild-type mice. CONCLUSIONS: In this murine model system, FTVII-dependent leukocyte recruitment, leukocyte activation via gp91(phox), and neutrophils are required for NSAID-induced gastrointestinal injury, whereas T and B cells are not essential.

Animals↗
PubMed2000

Crystallization and initial X-ray analysis of alkaline xylanase.

Crystals of alkaline xylanase (xylanase J) from alkaliphilic Bacillus sp. 41M-1 were grown by decreasing the temperature of the protein solution. Initial X-ray analysis of the crystal showed a tetragonal system with space group P4(1) or P4(3) and unit-cell parameters a = b = 115.7, c = 46.0 A. Assuming two molecules per asymmetric unit, V(m) = 2.31 A(3) Da(-1). The crystals diffract X-rays to 2.6 A resolution at 100 K.

Bacillus↗
PubMed2000

Individual sociodemographic characteristics associated with hospitalization for pediatric ambulatory care sensitive conditions.

This study examined the association of individual sociodemographic characteristics with pediatric ambulatory care sensitive condition (ACSC) hospitalizations in American hospitals while controlling for selected hospital characteristics. Data came from the 1994 National Hospital Discharge Survey. Bivariate statistical comparisons were performed to test the differences between ACSC and non-ACSC hospitalization rates in patient demographic and hospital characteristics. Logistic regression was followed to examine the relative significance of patient and hospital characteristics associated with pediatric ACSC hospitalizations. Such individual sociodemographic characteristics as age, race, and insurance status were significant predictors of ACSC hospitalization. Younger children were more likely to have ACSC hospitalization than older ones. Black children were 1.653 times more likely than white children to be hospitalized for ACSC (confidence interval = 1.53-1.79). Those with Medicaid or no secondary insurance were more likely to be hospitalized for ACSC than those with private insurance or with secondary insurance.

Adolescent↗
PubMed2000

Respiratory symptoms and use of medical care associated with child day care and health care plan among preschool children.

This study compared the risk of respiratory infections in pre-school children (under 6-year-old) attending day care center and those taken care of at home by controlling for the type of health plan and sociodemographic characteristics. The study population consists of members of two health plans residing in two South Carolina counties. Results show that the risks of respiratory symptoms were higher among children attending day care settings than those taken care of at homes although this relationship is more apparent among Medicaid children than among HMO children. While the type of child care has weak influence on medical care utilization, the type of health plan exerts strong influence on utilization for both day care and home care groups.

Chi-Square Distribution↗
PubMed1999

Targeted mutagenesis of Tsix leads to nonrandom X inactivation.

During X inactivation, mammalian female cells make the selection of one active and one inactive X chromosome. X chromosome choice occurs randomly and results in Xist upregulation on the inactive X. We have hypothesized that the antisense gene, Tsix, controls Xist expression. Here, we create a targeted deletion of Tsix in female and male mouse cells. Despite a deficiency of Tsix RNA, X chromosome counting remains intact: female cells still inactivate one X, while male cells block X inactivation. However, heterozygous female cells show skewed Xist expression and primary nonrandom inactivation of the mutant X. The ability of the mutant X to block Xist accumulation is compromised. We conclude that Tsix regulates Xist in cis and determines X chromosome choice without affecting silencing. Therefore, counting, choice, and silencing are genetically separable. Contrasting effects in XX and XY cells argue that negative and positive factors are involved in choosing active and inactive Xs.

Animals↗
PubMed1999

Genetic analysis of the mouse X inactivation center defines an 80-kb multifunction domain.

Dosage compensation in mammals occurs by X inactivation, a silencing mechanism regulated in cis by the X inactivation center (Xic). In response to developmental cues, the Xic orchestrates events of X inactivation, including chromosome counting and choice, initiation, spread, and establishment of silencing. It remains unclear what elements make up the Xic. We previously showed that the Xic is contained within a 450-kb sequence that includes Xist, an RNA-encoding gene required for X inactivation. To characterize the Xic further, we performed deletional analysis across the 450-kb region by yeast-artificial-chromosome fragmentation and phage P1 cloning. We tested Xic deletions for cis inactivation potential by using a transgene (Tg)-based approach and found that an 80-kb subregion also enacted somatic X inactivation on autosomes. Xist RNA coated the autosome but skipped the Xic Tg, raising the possibility that X chromosome domains escape inactivation by excluding Xist RNA binding. The autosomes became late-replicating and hypoacetylated on histone H4. A deletion of the Xist 5' sequence resulted in the loss of somatic X inactivation without abolishing Xist expression in undifferentiated cells. Thus, Xist expression in undifferentiated cells can be separated genetically from somatic silencing. Analysis of multiple Xic constructs and insertion sites indicated that long-range Xic effects can be generalized to different autosomes, thereby supporting the feasibility of a Tg-based approach for studying X inactivation.

Acetylation↗
PubMed1999

ELAV tumor antigen, Hel-N1, increases translation of neurofilament M mRNA and induces formation of neurites in human teratocarcinoma cells.

Human ELAV proteins are implicated in cell growth and differentiation via regulation of mRNA expression in the cytoplasm. In human embryonic teratocarcinoma (hNT2) cells transfected with the human neuronal ELAV-like protein, Hel-N1, neurites formed, yet cells were not terminally differentiated. Cells in which neurite formation was associated with Hel-N1 overexpression, also expressed increased levels of endogenous neurofilament M (NF-M) protein, which distributed along the neurites. However, steady-state levels of NF-M mRNA remained similar whether or not hNT2 cells were transfected with Hel-N1. These findings suggest that turnover of NF-M mRNA was not affected by Hel-N1 expression, despite the fact that Hel-N1 can bind to the 3' UTR of NF-M mRNA and was found directly associated with NF-M mRNA in transfected cells. Analysis of the association of NF-M mRNA with the translational apparatus in Hel-N1 transfectants showed nearly complete recruitment to heavy polysomes, indicating that Hel-N1 caused an increase in translational initiation. Our results suggest that the stability and/or translation of ARE-containing mRNAs can be regulated independently by the ELAV protein, Hel-N1, depending upon sequence elements in the 3' UTRs and upon the inherent turnover rates of the mRNAs that are bound to Hel-N1 in vivo.

3' Untranslated Regions↗
PubMed1999

Interleukin-2 receptoralpha gene expression in intestinal allograft rejection.

This study was undertaken to determine whether the interleukin-2 receptor alpha (IL-2Ralpha) coding gene could serve as a genetic marker of intestinal allograft rejection. The small bowel graft from Jinbai mice was heterotopically transplanted to BALB/c mice. Naive BALB/c mice and BALB/c mice with intestinal isografts were used as controls. The mRNA transcription level of the spleen cells harvested from the recipients and controls was measured with quantitative reverse transcription polymerase chain reaction (Q-RT-PCR) on postoperative day (POD) 3 and routine pathology was studied in these grafts. The IL-2Ralpha mRNA transcription level in untreated allografts was significantly higher than that of controls on POD 3, when intestinal allograft rejection was not detected. These data suggest that the IL-2Ralpha mRNA transcription level may reflect the early cellular immune response and this genetic marker may be of value in monitoring intestinal allograft rejection.

Animals↗
PubMed1999

Quantitative analysis of leukocyte dynamics in retinal microcirculation of rats with short-term ischemia-reperfusion injury.

PURPOSE: To characterize the time course of complete recovery of leukocyte velocities in the retinal microcirculation of rats from short-term (5-minute) retinal ischemia. METHODS: After 5 minutes of retinal ischemia produced by clamping the optic nerve, resulting in the occlusion of both central retinal artery and the central retinal vein, we used acridine orange (AO) and a scanning laser ophthalmoscope (SLO) to observe the velocities of leukocytes in precapillary arteriole ( v(a)), capillary (v(c)) and postcapillary venule (v(v)). Measurements were taken at reperfusion time points of 5, 10, 15, 20, 30, 40, 50, 60 and 80 minutes for the ischemic eyes and at 12, 22, 42 and 62 minutes for the control eyes, respectively. RESULTS: Each control velocity was arteriole 25.1 +/- 4.3 mm/ s; venule 16.9 +/- 3.2 mm/s; and capillary 1.54 +/- 0.31 mm/s, respectively. The leukocyte velocities after 5 minutes of ischemia in arteriole and venule recovered completely within 80 minutes of reperfusion; however, the recovery patterns were different. The recovery pattern showed a biphasic increase in arterioles and a monophasic increase in venules. The velocity in capillaries half recovered rapidly, within 5 minutes of reperfusion, but the subsequent recovery was slower and was not complete even at 80 minutes of reperfusion. CONCLUSIONS: In this study, leukocyte velocities in arterioles, venules and capillaries exhibited different recovery patterns following retinal ischemia and subsequent reperfusion. Capillaries, at least within 80 minutes of reperfusion, may have difficulty recovering completely from even short-term (5-minute) ischemia.

Acridine Orange↗
PubMed1998

The PACAP ligand/receptor system regulates cerebral cortical neurogenesis.

The PACAP ligand/type I receptor system is expressed throughout the embryonic nervous system, suggesting roles in regulating neural patterning and neurogenesis. In the forebrain, precursors of the six-layered cerebral cortex cease dividing in a highly reproducible spatiotemporal sequence. The time of cell cycle exit in fact determines neuron laminar fate. Our studies indicate that PACAP signaling may elicit cortical precursor withdrawal from the cell cycle, antagonizing mitogenic stimulators. PACAP inhibited embryonic day 13.5 rat cortical precursor [3H]thymidine incorporation, decreasing the proportion of mitotic cells. PACAP promoted morphological and biochemical differentiation, indicating that PACAP-induced cell cycle withdrawal was accompanied by neuronal differentiation. In vivo, embryonic cortex contains PACAP. In culture, 85% of cells expressed PACAP while 64% exhibited receptor. Co-localization studies indicated that PACAP ligand and receptor were expressed by the mitotic precursors that divided in response to bFGF, suggesting that precursors integrate mitogenic and anti-mitogenic signals to determine the timing of cell cycle exit. The expression of PACAP ligand and receptor in precursors raised the possibility of autocrine function. Indeed, peptide antagonists increased proliferation, suggesting that the PACAP system is expressed to elicit cell cycle exit. During ontogeny, an inhibitory signal, such as PACAP, may be required to counter the stimulatory activity of mitogenic bFGF and IGFI whose expression during cortical neurogenesis is sustained. The dynamic interplay of positive and negative regulators would regulate the timing of cell cycle withdrawal, and thus neuronal phenotype and laminar position.

Animals↗
PubMed1998

Tumor induction of VEGF promoter activity in stromal cells.

We have established a line of transgenic mice expressing the A. victoria green fluorescent protein (GFP) under the control of the promoter for vascular endothelial growth factor (VEGF). Mice bearing the transgene show green cellular fluorescence around the healing margins and throughout the granulation tissue of superficial ulcerative wounds. Implantation of solid tumors in the transgenic mice leads to an accumulation of green fluorescence resulting from tumor induction of host VEGF promoter activity. With time, the fluorescent cells invade the tumor and can be seen throughout the tumor mass. Spontaneous mammary tumors induced by oncogene expression in the VEGF-GFP mouse show strong stromal, but not tumor, expression of GFP. In both wound and tumor models the predominant GFP-positive cells are fibroblasts. The finding that the VEGF promoter of nontransformed cells is strongly activated by the tumor microenvironment points to a need to analyze and understand stromal cell collaboration in tumor angiogenesis.

Animals↗
PubMed1998

Opposing mitogenic regulation by PACAP in sympathetic and cerebral cortical precursors correlates with differential expression of PACAP receptor (PAC1-R) isoforms.

Neurogenesis in the peripheral and central nervous systems proceeds in region-specific fashion, although underlying mechanisms remain undefined. Emerging evidence indicates that the neuropeptide PACAP and its G-protein-coupled receptor are expressed widely in the embryonic brain, suggesting that the ligand/receptor system plays a role in development. We found previously that PAC1-R activation elicited opposing mitogenic effects in neurogenetic cultures, stimulating peripheral sympathetic neuroblasts while inhibiting cerebral cortical precursors. We have now defined the expression of PAC1-R mRNA isoforms and activation of second-messenger pathways in these model populations. Sympathetic neuroblasts express the "hop" receptor isoform, through which PACAP elicits increased levels of cAMP and activation of the PI signaling pathway. In contrast, cerebral cortical precursors express primarily the "short" (non-insert) receptor isoform and exhibit increased cAMP levels alone following PACAP treatment. Thus, opposing mitogenic regulation in sympathetic and cortical precursors correlates with differential receptor isoform expression and distinct second-messenger signaling. In addition to receptor, PACAP ligand mRNA was expressed by both populations, suggesting that the peptide is produced and acts locally to regulate precursor proliferation. These observations indicate that the PACAP ligand/receptor system is expressed in both the peripheral and central nervous system during development. More generally, these studies suggest that widely expressed extracellular factors mediate region-specific neurogenesis by activating lineage-restricted receptor isoforms and intracellular pathways.

Animals↗