Biomedical subjects

Ting Xie

Publications and source records attributed to Ting Xie.

26 records · Page 2Linked to original sources

PubMed2004

Synthesis of Eu2O3 nanotube arrays through a facile sol-gel template approach.

Eu2O3 nanotubes have been successfully fabricated by an improved sol-gel template method within the nanochannels of porous anodic alumina templates. The morphology, structure, and composition of the nanotubes were characterized by means of X-ray diffraction techniques, scanning electron microscope, transmission electron microscopy, and selected-area electron diffraction. The results show that the Eu2O3 nanotubes are polycrystalline with a cubic structure. The outer diameter of nanotubes is 50-80 nm, and the thickness of the tube wall is about 5 nm. The mechanism of nanotube formation was discussed.

Journal Article↗

PubMed2004

Gbb/Bmp signaling is essential for maintaining germline stem cells and for repressing bam transcription in the Drosophila testis.

Stem cells are responsible for replacing damaged or dying cells in various adult tissues throughout a lifetime. They possess great potential for future regenerative medicine and gene therapy. However, the mechanisms governing stem cell regulation are poorly understood. Germline stem cells (GSCs) in the Drosophila testis have been shown to reside in niches, and thus these represent an excellent system for studying relationships between niches and stem cells. Here we show that Bmp signals from somatic cells are essential for maintaining GSCs in the Drosophila testis. Somatic cyst cells and hub cells express two Bmp molecules, Gbb and Dpp. Our genetic analysis indicates that gbb functions cooperatively with dpp to maintain male GSCs, although gbb alone is essential for GSC maintenance. Furthermore, mutant clonal analysis shows that Bmp signals directly act on GSCs and control their maintenance. In GSCs defective in Bmp signaling, expression of bam is upregulated, whereas forced bam expression in GSCs causes the GSCs to be lost. This study demonstrates that Bmp signals from the somatic cells maintain GSCs, at least in part, by repressing bam expression in the Drosophila testis. dpp signaling is known to be essential for maintaining GSCs in the Drosophila ovary. This study further suggests that both Drosophila male and female GSCs use Bmp signals to maintain GSCs.

Activin Receptors, Type II↗

PubMed2004

Bmp signals from niche cells directly repress transcription of a differentiation-promoting gene, bag of marbles, in germline stem cells in the Drosophila ovary.

The Drosophila ovary is an attractive system to study how niches control stem cell self-renewal and differentiation. The niche for germline stem cells (GSCs) provides a Dpp/Bmp signal, which is essential for GSC maintenance. bam is both necessary and sufficient for the differentiation of immediate GSC daughters, cystoblasts. Here we show that Bmp signals directly repress bam transcription in GSCs in the Drosophila ovary. Similar to dpp, gbb encodes another Bmp niche signal that is essential for maintaining GSCs. The expression of phosphorylated Mad (pMad), a Bmp signaling indicator, is restricted to GSCs and some cystoblasts, which have repressed bam expression. Both Dpp and Gbb signals contribute to pMad production. bam transcription is upregulated in GSCs mutant for dpp and gbb. In marked GSCs mutant for Med and punt, two essential Bmp signal transducers, bam transcription is also elevated. Finally, we show that Med and Mad directly bind to the bam silencer in vitro. This study demonstrates that Bmp signals maintain the undifferentiated or self-renewal state of GSCs, and directly repress bam expression in GSCs by functioning as short-range signals. Thus, niche signals directly repress differentiation-promoting genes in stem cells in order to maintain stem cell self-renewal.

Animals↗

PubMed2004

[The influence of L-arginine on the angiogenesis in burn wounds in diabetic rats].

OBJECTIVE: To investigate the possible mechanism of L-arginine supplementation on the angiogenesis of burn wounds in diabetic rats. METHODS: One hundred male Sprague-Dawley (SD) rats were used in the study and were randomly divided into A (scalding control, n = 25), B (scalding of the rats with diabetes, n = 25), C (L-glycine control, n = 25) and D (L-arginine supplementation, n = 25) groups. Diabetes was produced by intra-peritoneal injection of streptozotocin (STZ) in B, C and D groups. The rats in C and D groups were gavaged with L-glycine and L-arginine in dose of 200 mg.kg(-1).d(-1), respectively. The glucose content of the back skin tissue was determined for five rats in each group eight weeks after STZ administration. Deep partial thickness scalding of 20% TBSA was engendered on the back in the other 80 rats. The wound area, wound healing rate, and microvascular density with CD34 immunohistochemistry staining were determined on 3rd, 7th, 14th, and 21st post scalding days (PSDs), In addition, the amount of nitric oxide (NO) released from the wound tissue and the tissue contents of vascular endothelial growth factor (VEGF) and transforming growth factor beta1 (TGF-beta1) from wound were determined at the above time points. RESULTS: Compared to those in group B, the wound healing rate in group D increased significantly since the 7th PSD [(44.10 +/- 3.50)%, P < 0.05], and the wound MVD value was increased significantly at all postburn time points. Furthermore, the levels of VEGF, NO and TGF-beta1 in the wound tissue was also increased significantly, while the glucose content in the cutaneous tissue was decreased to (1.380 +/- 0.120) mg/g. CONCLUSION: L-arginine supplementation could be beneficial to the angiogenesis in the burn wound of the rats with diabetes, as well as to wound healing by increasing the synthesis and the release of VEGF, NO and TGF-beta1 from burn wound and by decreasing the glucose content in the cutaneous tissue of diabetic rats.

Animals↗

PubMed2003

Clonal expansion of ovarian germline stem cells during niche formation in Drosophila.

Stem cell niches are specific regulatory microenvironments formed by neighboring stromal cells. Owing to difficulties in identifying stem cells and their niches in many systems, mechanisms that control niche formation and stem cell recruitment remain elusive. In the Drosophila ovary, two or three germline stem cells (GSCs) have recently been shown to reside in a niche, in which terminal filaments (TFs) and cap cells are two major components. We report that signals from newly formed niches promote clonal expansion of GSCs during niche formation in the Drosophila ovary. After the formation of TFs and cap cells, anterior primordial germ cells (PGCs) adjacent to TFs/cap cells can develop into GSCs at the early pupal stage while the rest directly differentiate. The anterior PGCs are very mitotically active and exhibit two division patterns with respect to cap cells. One of these patterns generates two daughters that both contact cap cells and potentially become GSCs. Our lineage tracing study confirms that one PGC can generate two or three GSCs to occupy a whole niche ('clonal expansion'). decapentaplegic (dpp), the Drosophila homolog of human bone morphogenetic protein 2/4, is expressed in anterior somatic cells of the gonad, including TFs/cap cells. dpp overexpression promotes PGC proliferation and causes the accumulation of more PGCs in the gonad. A single PGC mutant for thick veins, encoding an essential dpp receptor, loses the ability to clonally populate a niche. Therefore, dpp is probably one of the mitotic signals that promote the clonal expansion of GSCs in a niche. This study also suggests that signals from newly formed niche cells are important for expanding stem cells and populating niches.

Animals↗

PubMed2003

Wingless signaling regulates the maintenance of ovarian somatic stem cells in Drosophila.

Identifying the signals involved in maintaining stem cells is critical to understanding stem cell biology and to using stem cells in future regenerative medicine. In the Drosophila ovary, Hedgehog is the only known signal for maintaining somatic stem cells (SSCs). Here we report that Wingless (Wg) signaling is also essential for SSC maintenance in the Drosophila ovary. Wg is expressed in terminal filament and cap cells, a few cells away from SSCs. Downregulation of Wg signaling in SSCs through removal of positive regulators of Wg signaling, dishevelled and armadillo, results in rapid SSC loss. Constitutive Wg signaling in SSCs through the removal of its negative regulators, Axin and shaggy, also causes SSC loss. Also, constitutive wg signaling causes over-proliferation and abnormal differentiation of somatic follicle cells. This work demonstrates that wg signaling regulates SSC maintenance and that its constitutive signaling influences follicle cell proliferation and differentiation. In mammals, constitutive beta-catenin causes over-proliferation and abnormal differentiation of skin cells, resulting in skin cancer formation. Possibly, mechanisms regulating proliferation and differentiation of epithelial cells, including epithelial stem cells, is conserved from Drosophila to man.

Animals↗

PubMed2002

DE-cadherin-mediated cell adhesion is essential for maintaining somatic stem cells in the Drosophila ovary.

Evidence from many systems has shown that stem cells are maintained in "niches" or specific regulatory microenvironments formed by stromal cells. The question of how stem cells are maintained in their niches is important, and further studies will lead to a better understanding of stem cell regulation and enhance the future use of stem cells in regenerative medicine. Here we show that cadherin-mediated cell adhesion is required for anchoring somatic stem cells (SSCs) to their niches in the Drosophila ovary. DE-cadherin and Armadillo/beta-catenin accumulate in the junctions between SSCs and their neighboring cells, inner germarial sheath cells. Removal of DE-cadherin from SSCs results in stem cell loss in the adult ovary. Furthermore, the cadherin-mediated adhesion is also important for maintaining SSCs in their niches before adulthood. This study provides further support that SSCs are located in a niche formed by their neighboring cells. We have previously shown that DE-cadherin-mediated cell adhesion is essential for anchoring germ-line stem cells to their niches in the Drosophila ovary. This study further implicates cadherin-mediated cell adhesion as a general mechanism for anchoring stem cells to their niches in a variety of systems.

Animals↗

PubMed2002

Germline stem cells anchored by adherens junctions in the Drosophila ovary niches.

How stem cells are recruited to and maintained in their niches is crucial to understanding their regulation and use in regenerative medicine. Here, we demonstrate that DE-cadherin-mediated cell adhesion is required for anchoring germline stem cells (GSCs) in their niches in the Drosophila ovary. Two major components of this adhesion process, DE-cadherin and Armadillo/beta-catenin, accumulate at high levels in the junctions between GSCs and cap cells, one of the niche components. Removal of these proteins from GSCs results in stem cell loss. Furthermore, DE-cadherin is required for recruiting GSCs to their niche. Our study demonstrates that anchorage of GSCs in their niche by DE-cadherin-mediated adhesion is important for stem cell maintenance and function.

Adherens Junctions↗