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Biomedical subjects

J Cheng

Publications and source records attributed to J Cheng.

At least 361 records · Page 20Linked to original sources
PubMed1995

CD34+ endothelial cell lines derived from murine yolk sac induce the proliferation and differentiation of yolk sac CD34+ hematopoietic progenitors.

Embryonic hematopoiesis is initiated in part in the blood islands of the yolk sac. Previous confocal microscopic analysis has shown that the CD34 antigen, a mucin-like cell surface glycoprotein that is expressed by hematopoietic progenitors and all endothelial cells of the adult and embryo, is also found on a subset of luminal hematopoietic-like cells in the yolk sac blood islands as well as on the vascular endothelium lining these early hematopoietic locations. We show here that, as in all other hematopoietic sites thus far examined, immunoaffinity-purified CD34+ nonadherent cells from murine yolk sacs contain the vast majority of erythroid and myeloid progenitor cell colony forming activity. To examine the developmental interactions between these CD34+ hematopoietic progenitor cells of the yolk sac and the CD34+ yolk sac endothelium, we have immunaffinity-purified adherent endothelial cells from day 10.5 yolk sacs using CD34 antiserum and produced cell lines by transformation with a retrovirus expressing the polyoma middle T antigen. Analysis of these cell lines for CD34, von Willebrand's factor, FLK 1 and FLT 1 expression, and capillary growth in Matrigel indicates that they appear to be endothelial cells, consistent with their original phenotype in vivo. Coculture of yolk sac CD34+ hematopoietic cells on these endothelial cell lines results in up to a 60-fold increase in total hematopoietic cell number after approximately 8 days. Analysis of these expanded hematopoietic cells showed that the majority were of the monocyte/macrophage lineage. In addition, examination of the cultures showed the rapid formation of numerous cobblestone areas, a previously described morphologic entity thought to be representative of early pluripotential stem cells. Scrutiny of the ability of these endothelial cell lines to expand committed progenitor cells showed up to a sixfold increase in erythroid and myeloid colony-forming cells after 3 to 6 days in culture, consistent with the notion that these embryonic endothelial cells mediate the expansion of these precursor cells. Polymerase chain reaction analyses showed that most of the cell lines produce FLK-2/FLT-3 ligand, stem cell factor, macrophage colony-stimulating factor, leukemia-inhibitory factor, and interleukin-6 (IL-6), whereas there is a generally low or not measurable production of granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, IL-1, IL-3, transforming growth factor beta-1, erythropoietin, or thrombopoietin. The output of mature hematopoietic cells from these cocultures can be modified to include an erythroid population by the addition of exogenous erythropoietin. These data suggest that endothelial cell lines derived form the yolk sac provide an appropriate hematopoietic environment for the expansion and differentiation of yolk sac progenitor cells into at least the myeloid and erythroid lineages.

Animals↗
PubMed1995

Movement-induced depression of soleus H reflexes is consistent in humans over the range of excitatory afferents involved.

The presumption that the H reflex arises exclusively from Ia afferent discharge has been challenged. If the reflex is comprised of many afferent responses, then movement-induced H reflex inhibition witnessed at one point in the recruitment curve may be quite different from the inhibition at another point in the curve. H reflex recruitment curves were constructed for three subjects during passive pedalling, isolated knee rotation and isolated hip rotation. Compared to control recruitment curves, these curves were reduced across the full spectrum of stimulus intensities. This suggests one of two possibilities: (1) all afferents contributing to the H reflex are subject to the same source and modality of inhibition; or (2) there is only one afferent type contributing to the reflex.

Adult↗
PubMed1995

Differential expression of human Fas mRNA species upon peripheral blood mononuclear cell activation.

Human Fas/Apo-1 is a cell-surface protein that mediates apoptosis upon ligation with Fas ligand. The gene lies on the long arm of chromosome 10, consists of nine exons, and spans more than 26 kb of DNA. We previously reported the presence of a Fas variant mRNA, designated as Fas delta TM, in human peripheral blood mononuclear cells. Fas delta TM is generated by alternative splicing of the intact exon 6, which encodes the Fas transmembrane domain. In the present study, we describe three novel forms of Fas mRNA that are generated by alternative splicing of exons 3, 4, 6 and 7. These three mRNA variants undergo a frameshift and produce truncated polypeptides because of the appearance of a stop codon in the altered open reading frame. On activation of the peripheral blood mononuclear cells, a decreased expression of alternatively spliced Fas mRNA species correlated with increased cell-surface expression of Fas. These results suggest that differential expression of alternatively spliced Fas mRNAs may play a role in regulation of Fas function via regulation of the production of the membrane-bound and the soluble, secreted Fas protein products.

Alternative Splicing↗
PubMed1995

Immune responses to nucleic acid vaccines to rabies virus.

A plasmid vector expressing the full-length rabies virus glycoprotein (G protein) under the control of the simian virus 40 (SV40) promoter has previously been shown to induce upon intramuscular (i.m.) inoculation into mice a specific B- and T-cell-mediated immune response and protection against challenge with a virulent strain of the virus. Here we tested two parameters that might affect the efficacy of this DNA vaccine. First, we replaced the SV40 promoter of the original vector with the early promoter derived from cytomegalovirus leaving all other parameters of the plasmid intact. Although upon transfection in vitro the two vectors showed a striking difference in their ability to cause stable expression of the rabies virus G protein, upon i.m. inoculation into mice both constructs induced comparable immune responses. Second, we constructed a vector that induces expression of a secreted form of rabies G protein by inserting a stop codon just upstream of the transmembrane domain of the rabies G protein gene. The immune responses to the DNA vaccines expressing the two different forms of the G protein, secreted and membrane bound, were compared and found to be similar in magnitude. The long-term effect of DNA vaccination was also investigated especially with regard to adverse immunological reactions such as the induction of unresponsiveness against rabies virus and the development of antibodies to DNA. DNA vaccination was found to induce long-lasting immunity to rabies virus without apparent negative side effects such as development of T cell tolerance or generation of anti-DNA antibodies.

Animals↗
PubMed1995

Long-lasting conditioning of the human soleus H reflex following quadriceps tendon tap.

Percussion of the quadriceps tendon was used to test the hypothesis that knee extensor muscle spindle discharge initiates down-regulation of the gain of the soleus H reflex. Seven subjects participated. Soleus H reflex magnitude was observed for up to 15 s, following conditioning tendon taps of 60 N or 80 N force and 10 ms duration, with the knee at 60 degrees or 90 degrees of flexion. The tap elicited quadriceps stretch reflexes in four subjects, with a mean latency of 42 ms. The major component of the conditioning of the soleus H reflex was significant attenuation of magnitude by 30-90% of controls, starting as early as 36 ms post-percussion and lasting as long as 3-8 s. The attenuation of reflex magnitude was evident, whichever combination of duration and force of tap was used. Preceding and/or following this inhibition, there was mild facilitation. Static stretch of quadriceps also significantly reduced soleus H reflex magnitude. These results support the spindle receptor origin for the gain attenuation seen during movement. The time course of the gain attenuation suggests a spinal route, by which the spindle discharge of the heteronymous extensor muscles initiates presynaptic inhibition of transmission through the reflex pathway.

Adult↗
PubMed1995

Correlating the pharmacology and molecular biology of opioid receptors. Cloning and antisense mapping a kappa 3-related opiate receptor.

We cloned a kappa 3-related opioid receptor, and although it is still not clear whether this clone corresponds to the kappa 3 receptor itself or is a related gene product, the extensive antisense mapping and the antibody immunoreactivity strongly associate this clone with the kappa 3 receptor. Our approach also indicates the usefulness of antisense approaches in mapping and identifying orphan receptors. Perhaps it is most effective in identifying partial sequences prior to cloning them in their entirety. It also provides a mechanism of identifying proteins that are not expressed functionally.

Animals↗
PubMed1995

Long-lasting inhibition of the human soleus H reflex pathway after passive movement.

Human soleus H reflexes are attenuated during passive pedalling movements. This depression occurs within 70 ms of movement onset. We hypothesized that the reflex gain would return to control values with a similar brevity following movement. However, H reflexes sampled following a slow (10 rpm) passive pedalling movement of a single leg remained below control values for the duration of a 200 ms collection period, for all four pedal positions tested. The extent of the attenuation after movement was position dependent in a manner similar to that observed during movement. This position effect was more precisely defined by sampling reflexes 200 ms post-movement at 10 pedal crank positions. Also, the full course of reflex recovery was investigated by sampling up to 8 s post-movement at four pedal positions. Reflex gain remained reduced 1-4 s post-movement, in a position dependent manner. There was a subsequent facilitation of the reflex. Thus, following a locomotor-like movement there is sustained attenuation of the soleus H reflex. The early post-movement period is likely the continued expression of movement-induced reflex inhibition while the later period may arise from descending influences consequent to the termination of movement. Presynaptic inhibition is implicated, as reflexes still showed the gain modulation when sampled while soleus was tonically contracted, both following and during the passive movement.

Adult↗
PubMed1995

The relationship between the kinematics of passive movement, the stretch of extensor muscles of the leg and the change induced in the gain of the soleus H reflex in humans.

The gain of the H reflex attenuates during passive stepping and pedalling movements of the leg. We hypothesized that the kinematics of the movement indirectly reflect the receptor origin of this attenuation. In the first experiment, H reflexes were evoked in soleus at 26 points in the cycle of slow, passive pedalling movement of the leg and at 13 points with the leg static (the ankle was always immobilized). Maximum inhibition occurred as the leg moved through its most flexed position (P < 0.05). Inhibition observed in the static leg was also strongest at this position (P < 0.05). The increase in inhibition was gradual during flexion movement, with rapid reversal of this increase during extension. In the second experiment, the length of stretch of the vasti muscles was modelled. Variable pedal crank lengths and revolutions per minute (rpm) altered leg joint displacements and angular velocities. Equivalent rates of stretch of the vasti, achieved through different combinations of joint displacements and velocities, elicited equivalent attenuations of mean reflex magnitudes in the flexed leg. Reflex gain exponentially related to rate of stretch (R2 = 0.98 P < 0.01). The results imply that gain attenuation of this spinal sensorimotor path arises from spindle discharge in heteronymous extensor muscles of knee and/or hip, concomitant with movement.

Adult↗
PubMed1995

Characterization of human Fas gene. Exon/intron organization and promoter region.

Ligation of the Fas cell-surface molecule induces apoptosis. Defective Fas-mediated apoptosis has been associated with spontaneous autoimmunity in mice. Using human Fas/Apo-1 cDNA as a probe, we have molecularly cloned and characterized the human Fas chromosomal gene. The gene consists of nine exons and spans more than 26 kilobases of DNA. The lengths of introns vary from > 14 kilobases at the 5' end of the gene to 152 base pairs upstream of the exon encoding the transmembrane domain. The domain structure of the human Fas is encoded by an exon or a set of exons. Primer extension analysis revealed three major transcription initiation sites. The promoter region lacked canonical "TATA" and "CAAT" boxes but was a "GC-rich" sequence, and contained consensus sequences for AP-1, GF-1, NY-Y, CP-2, EBP20, and c-myb. These data provide the first characterization of the human Fas gene and insight into its regulatory region.

Amino Acid Sequence↗
PubMed1995

Autoimmunity, apoptosis defects and retroviruses.

Autoimmunity and AIDS both share the common feature of increased expression of retroviral protein products and abnormal apoptosis of immune cells (81). This leads to a more global immunomodulatory defect (82-84). The challenge in the future will be to devise compounds that can either regulate the effect of the retroviral products on apoptosis, or that can inhibit apoptosis pathways in order to restore normal immune system function.

Amino Acid Sequence↗
PubMed1995

Biosynthesis of basement membrane molecules by salivary adenoid cystic carcinoma cells: an immunofluorescence and confocal microscopic study.

The biosynthesis of basement membrane molecules and fibronectin was studied in vitro in the two different human cell systems (ACC2 and ACC3) established from adenoid cystic carcinomas (ACC) of the salivary gland using immunofluorescence and confocal microscopy. When cells were attached and spread on dishes, fine granular immunofluorescence for type IV collagen, laminin, heparan sulphate proteoglycan, entactin, and fibronectin first appeared diffusely in the cytoplasm, and then changed in aggregation of coarse granules in the perinuclear area. With formation of colonies, these signals were present in the extracellular space, initially in the basal aspect of attached cells and consequently in the lateral intercellular space. After the cells formed a confluent monolayer, extracellular signals started to decrease in inverse proportion to the reappearance of intracellular ones. The results indicate that the parenchymal cells of ACC synthesize these five extracellular matrix molecules, secrete them into the extracellular milieu and remodel the extracellular deposits. It is suggested that the characteristic stromal architecture of ACC, represented by stromal pseudocysts, results from their own secretion of the basement membrane molecules and fibronectin.

Adult↗
PubMed1995

Rapid optimization of electroporation conditions for plant cells, protoplasts, and pollen.

The optimization of electroporation conditions for maximal uptake of DNA during direct gene transfer experiments is critical to achieve high levels of gene expression in transformed plant cells. Two stains, trypan blue and fluorescein diacetate, have been applied to optimize electroporation conditions for three plant cell types, using different square wave and exponential wave electroporation devices. The different cell types included protoplasts from tobacco, a stable mixotrophic suspension cell culture from soybean with intact cell walls, and germinating pollen from alfalfa and tobacco. Successful electroporation of each of these cell types was obtained, even in the presence of an intact cell wall when conditions were optimized for the electroporation pulse. The optimal field strength for each of these cells differs, protoplasts having the lowest optimal pulse field strength, followed by suspension cells and finally germinating pollen requiring the strongest electroporation pulse. A rapid procedure is described for optimizing electroporation parameters using different types of cells from different plant sources.

Electroporation↗
PubMed1995

The effect of levonorgestrel-releasing intrauterine device (20 micrograms/day) (LNG-IUD-20) on the morphological structure of human endometrium: a study of the endometrial factor VIII activity in the women before and after insertion of LNG-IUD-20 by the digital image analysis.

The specimens of endometria were obtained from 18 women using an intrauterine device releasing levonorgestrel at 20 micrograms/day (LNG-IUD-20). An immunoperoxidase reaction, PAP method, with the antiserum of Factor VIII as the primary antibody, was carried out in the endometrial biopsies to detect the Factor VIII activity in the endometrial endothelium before and after insertion of LNG-IUD-20. The immunoperoxidase activity was quantitatively assessed by a computer digital image analyser. The results revealed that there were a lower Factor VIII activity in the endometrial endothelial cells after insertion of LNG-IUD-20 (p < 0.001) when compared with the control. From the results of the present study, it is suggested that the synthesis and release of endometrial endothelial Factor VIII might be inhibited by the insertion of LNG-IUD20.

Adult↗
PubMed1995

Primary leiomyosarcoma of the maxilla with regional lymph node metastasis. Report of a case and review of the literature.

A rare case of oral leiomyosarcoma diagnosed with the aid of immunohistochemical and electron microscopic examinations together with a review of the literature are reported. The patient was a 70-year-old Japanese man. The primary tumor involved the maxillary gingiva and bone and metastasized to the cervical lymph nodes. On histologic examination the tumor showed invasive growth into the maxillary bone. It was composed of interlacing fascicles of spindle-shaped cells with eosinophilic cytoplasm and elongated, blunt-ended nuclei. The tumor formed extensive metastatic foci in the cervical lymph nodes. On immunohistochemical examination most of the tumor cells were positive for desmin, smooth muscle-specific actin, and myosin. The ultrastructural characteristics of the tumor cells were abundant microfilaments, pinocytotic vesicles, and basement membrane formation. The findings were indicative of a tumor demonstrating myogenic differentiation. A review of the literature during the past 50 years disclosed a total of 60 oral leiomyosarcomas, including our case.

Actin Cytoskeleton↗