PubMed Health⌕ Search

Biomedical subjects

X M Xu

Publications and source records attributed to X M Xu.

At least 73 records · Page 4Linked to original sources
PubMed1994

Developmental plasticity of reticulospinal and vestibulospinal axons in the north American opossum, Didelphis virginiana.

We have shown previously that rubral axons grow around a lesion of their spinal pathway in the North American opossum if it is made at early stages of development. In the present experiments, we have asked whether reticular and vestibular axons have the same ability. The spinal cord was hemisected at postnatal day 20, 12, or 5, well within the critical period for rubrospinal plasticity, and, approximately 30 days later, bilateral injections of fast blue were made about four segments caudal to the lesion. The pups were killed 4 or 5 days after the injections. In most of the animals lesioned on postnatal day 20, labeled neurons were not found in the medial part of the pontine reticular nucleus or the dorsal part of the lateral vestibular nucleus ipsilateral to the lesion. The spinal projections from both areas are exclusively ipsilateral. When the lesions were made at postnatal day 12 or 5, however, labeled neurons were present in both areas, suggesting that they supported axons that had grown caudal to the lesion. As was expected from previous studies, rubral neurons were labeled contralateral to the lesion in all three groups. In the opossum, as in other species, the red nucleus projects contralaterally. We conclude that reticular and vestibular axons, like axons from the red nucleus, grow around a lesion of their pathway during development and that the critical period for their plasticity ends earlier than that for rubrospinal axons.

Animals↗
PubMed1994

Characterization of the genomic structure, chromosomal location and promoter of human prostaglandin H synthase-2 gene.

Prostaglandin H synthase (PGHS) is the rate-limiting enzyme in the conversion of arachidonic acid to prostanoids. The human PGHS has two isoforms. PGHS-1 is a house keeping gene whereas PGHS-2 is an inducible gene. We reported here the isolation of the entire PGHS-2 gene and its 5'-flanking region from a human bacteriophage P1 genomic library. The gene containing 10 exons is 7.5 kb in length and located at chromosome 1. The transcriptional start site was mapped at 134 bases upstream from the ATG start codon. Nucleotide sequence of 1.8 kb promoter region contains a TATA box and a number of potential regulatory elements including CRE, NF-kappa B, Sp1 and AP2 sites. Studies of the promoter activity showed that the first 460 nucleotides of 5'-flanking region efficiently drove transcription of the luciferase reporter gene in human umbilical vein endothelial cells upon stimulation with phorbor ester.

Animals↗
PubMed1994

[Transurethral non-contact laser treatment of prostatic hypertrophy].

66 cases of prostatic hypertrophy have been treated by transurethral non-contact Nd:YAG laser irradiation since April 1993. Sixty patients regained unobstructed urination within 1 week and 6 within 2 weeks after operation. The symptoms of the treated group were improved with the necrotic tissues gradually peeling off in 3 to 6 weeks. The short-term follow-up indicated that the prostatic gland distinctly reduced and residual urine decreased or vanished after treatment. Three patients had one of the following complications: urinary tract infection, epididymitis or urinous infiltration. These complications were treated appropriately. This therapy is ideal for the treatment of prostatic hypertrophy.

Aged↗
PubMed1994

[Transurethral laser prostatectomy: report of 200 cases].

From August 1988 to May 1993, 200 patients with benign prostatic hyperplasia (BPH) were treated by transurethral laser prostatectomy (TULP) in our hospital. 165 patients were followed up for 6 months to 4.5 years and the results showed excellent effect in 128 cases, improved 32 cases, the total effectiveness was 97%. TULP, a safe and effective therapy for BPH, have more wide operative indication range but it is not suitable for patients with carcinoma of prostate.

Aged↗
PubMed1994

[Molecular screening and prenatal diagnosis of the deletional alpha-thalassemia by polymerase chain reaction amplification].

For the genetic counselling, 8,432 blood samples from Chinese couples were screened for detecting alpha-thalassemia in Guangzhou city. The positive diagnosis of 646 (7.66%) alpha-thalassemia patients was made. One hundred DNA random samples from the above positive cases were collected and were analysed by using polymerase chain reaction (PCR) to determine the genotype of alpha-thalassemia of Southeast Asian deletion(--SEA/). Of 100 alpha-thalassemia individuals screened for the (--SEA/) mutation, 99 (96 with alpha-thalassemia trait and 3 with hemoglobin H disease) were detected by the present method. This mutation was not found in the remaining one with alpha-thalassemia compound Hb Q. We also used this assay to analyse DNA samples from cord blood in 6 pregnancies at risk of Bart's hydrops fetalis, in 1 at risk of Hb H disease for prenatal diagnosis.

Female↗
PubMed1994

Gene therapy for vascular diseases.

Gene transfer by virus- and liposome-mediated vectors has potential for treating genetic diseases, cancer, and cardiovascular diseases. In this article, we discuss the general principle and techniques for gene transfer and the specific issues facing therapy for vascular diseases. We also propose a strategy for using virus-mediated gene transfer to restore the vasoprotective function of the vascular wall, thereby preventing vascular thrombosis. Experimental data from ongoing work in our laboratories are presented to illustrate the importance of this approach in vascular gene transfer therapy.

Gene Transfer Techniques↗
PubMed1993

Characterization of the promoter of human prostaglandin H synthase-1 gene.

The gene of human prostaglandin H synthase-1 (PGHS-1,EC 1.14.99.1) was isolated from a human cosmid library and was contained in two overlapping clones. Multiple transcriptional start sites were identified. The major one located 136 bases upstream from the ATG initiation codon. The promoter region contains no canonical TATA box but possesses a high G+C content. These observations suggest that PGHS-1 gene has the characteristics of a housekeeping gene. Both 0.8 and 0.4 kb of the 5'-flanking sequence of the PGHS-1 gene can confer transcriptional activity.

Animals↗
PubMed1993

Direct genotyping and prenatal diagnosis of beta-thalassemia in Chinese by polymerase chain reaction mediated restriction fragment length polymorphism method.

The molecular basis of beta-thalassemia is predominantly point mutations in the beta-globin gene. Frameshift 41-42 (-CTTT), IVS-2 position 654 (C-->T) mutation, nonsense codon 17 (A-->T), TATA box position -28 (A-->G) mutation and frameshift 71-72 (+A) account for more than 95% of beta-thalassemia alleles in the population of South China. We have developed a polymerase chain reaction (PCR)-mediated restriction fragment length polymorphism (RFLP) method for the identification of these alleles. In this method, artificial mispairing bases in PCR-amplified products were created to distinguish normal from mutant alleles on the basis of RFLPs. The size of the five PCR-amplified DNA fragments that may potentially contain the above five types of mutations is 93 or 89 bp (codons 41-42), 221 bp (IVS-2 nt 654), 110 bp (codon 17), 123 bp (TATA box nt -28), and 97 or 98 bp (codons 71-72). After these fragments were digested with Hinc II, Mae III, Nhe I, EcoR I, and Dde I, respectively, the allele-specific RFLPs produced were analyzed by gel electrophoresis. DNA samples of 24 patients with the above five types of beta-thalassemia were investigated with the present method and allele-specific oligonucleotide (ASO) probing simultaneously. We used this method in the prenatal diagnosis of 14 Chinese families for beta-thalassemia. The results obtained by the present method correspond well with those by the ASO probe test.

Adult↗
PubMed1993

The origins of descending projections to the lumbar spinal cord at different stages of development in the North American opossum.

We have employed the retrograde transport of fast blue (FB) to identify the origins of descending projections to the lumbar cord of the opossum from postnatal day (PD)1, 12-13 days after conception, to maturity. When FB injections were made into the lumbar cord at PD1, supraspinal labeling was sparse and limited to the hypothalamus, the reticular formation, the coeruleus complex, the caudal raphe, and, in one case, the interstitial nucleus of the medial longitudinal fasciculus and the lateral vestibular nucleus. Only a few propriospinal neurons were labeled at cervical and thoracic levels. By PD3, however, supraspinal and propriospinal labeling was abundant and present in most of the areas labeled in the adult animal. A notable exception was the red nucleus which was not labeled until approximately PD10. Our results have been compared with those described in other species and discussed in light of their relevance to the development of descending control over hindlimb movement and developmental plasticity of descending spinal pathways.

Amidines↗
PubMed1993

Enhanced prostacyclin synthesis in endothelial cells by retrovirus-mediated transfer of prostaglandin H synthase cDNA.

A retroviral vector (BAG) was used to transfer human prostaglandin H synthase (PGHS-1) gene into a human endothelial cell line for enhancement of PGI2 synthesis. Cells infected with BAG containing PGHS-1 cDNA in the sense orientation relative to the retroviral promoter (PGHS(S)) expressed a 30-fold increase in mRNA but, due to a reading frame shift, did not show an increase in PGHS protein or in PGI2 synthesis, while those with PGHS-1 in reverse orientation relative to the viral promoter (PGHS(R)), produced a > 10-fold increase in PGHS mRNA over the control (169 +/- 22 vs 14.8 +/- 1.2 amol/micrograms RNA) with a concordant increase in PGHS protein (5.82 +/- 1.07 vs 0.23 +/- 0.04 ng/mg protein) and enzyme activity. Primer extension analysis of PGHS(R) revealed two transcription start sites located in the SV40 late promoter region adjacent to PGHS-1 cDNA. PGHS(R) cells produced a high basal PGI2 level which was increased by several-fold in response to stimulation by ionophore, arachidonic acid, and thrombin. Kinetic analysis revealed the PGI2 synthetic rate to be 14 ng/min-1 per million cells and t1/2 of PGI2 synthesis, 13.3 min. These findings indicate that transfer of PGHS-1 gene into vascular cells enhances PGI2 synthesis and may be a useful strategy for restoring thromboprotective property of damaged blood vessels.

Amino Acid Sequence↗
PubMed1993

The developing organ of Corti contains retinoic acid and forms supernumerary hair cells in response to exogenous retinoic acid in culture.

The mammalian organ of Corti has one of the most highly ordered patterns of cells in any vertebrate sensory epithelium. A single row of inner hair cells and three or four rows of outer hair cells extend along its length. The factors that regulate the formation of this strict pattern are unknown. In order to determine whether retinoic acid plays a role during the development of the organ of Corti, exogenous retinoic acid was added to embryonic mouse cochleae in vitro. Exogenous retinoic acid significantly increased the number of cells that developed as hair cells and resulted in large regions of supernumerary hair cells and supporting cells containing two rows of inner hair cells and up to 11 rows of outer hair cells. The effects of retinoic acid were dependent on concentration and on the timing of its addition. Western blot analysis indicated that cellular retinoic acid binding protein (CRABP) was present in the sensory epithelium of the embryonic cochlea. The amount of CRABP apparently increased between embryonic day 14 and postnatal day 1, but CRABP was not detectable in sensory epithelia from adults. A retinoic acid reporter cell line was used to demonstrate that retinoic acid was also present in the developing organ of Corti between embryonic day 14 and postnatal day 1, and was also present in adult cochleae at least in the vicinity of the modiolus. These results suggest that retinoic acid is involved in the normal development of the organ of Corti and that the effect of retinoic acid may be to induce a population of prosensory cells to become competent to differentiate as hair cells and supporting cells.

Animals↗
PubMed1993

Quantitative analysis of vascular prostaglandin H synthase mRNA levels by competitive polymerase chain reaction.

Prostaglandin H synthase (PGHS) occupies a central position in the biosynthesis of prostaglandins, thromboxane, and prostacyclin. Expression of this enzyme is enhanced by inflammatory cytokines and phorbol esters. Because of the low abundance of PGHS, PGHS mRNA levels in tissues and cells were difficult to measure accurately. In this study, we quantified vascular PGHS-1 mRNA levels by a competitive polymerase chain reaction assay. The mean basal PGHS-1 level in cultured human umbilical vein endothelial cells (HUVECs) was 24.3 +/- 10.6 amol/microgram RNA. Treatment of the HUVECs with recombinant human interleukin-1 beta at 37 degrees C for 4 hours increased the mRNA to 49.1 +/- 9.1 amol/microgram RNA, a 2.1-fold increase. Treatment of the cells with phorbol 12-myristate 13-acetate at 37 degrees C for 4 hours caused a 1.7-fold increase in the mRNA level. This procedure was utilized to measure PGHS-1 mRNA levels in rabbit abdominal aorta, inferior vena cava, liver, kidney, and lung. The aortic mRNA level (9.2 +/- 1.9 amol/microgram RNA) was about 5 times higher than the inferior vena caval level (2.4 +/- 1.3 amol/microgram RNA) but only slightly higher than the level of other organs. These results reveal a significant difference in PGHS-1 mRNA levels between arterial and venous tissues. The synthase mRNA levels in organs such as liver, kidneys, and lungs do not differ significantly. The PCR assay should be valuable for studying the role of PGHS expression in disease states.

Animals↗