Biomedical subjects

Feng Ma

Publications and source records attributed to Feng Ma.

4 recordsLinked to original sources

PubMed2006

Sequential analysis of alpha- and beta-globin gene expression during erythropoietic differentiation from primate embryonic stem cells.

The temporal pattern of embryonic, fetal, and adult globin expression in the alpha (zeta --> alpha) and beta (epsilon --> gamma and gamma --> beta) clusters were quantitatively analyzed at the transcriptional and translational levels in erythrocytes induced from primate embryonic stem cells in vitro. When vascular endothelial growth factor receptor-2(high) CD34(+) cells were harvested and reseeded onto OP9 stromal cells, two-wave erythropoiesis occurred sequentially. Immunostaining and real-time reverse transcription-polymerase chain reaction analyses of floating mature erythrocytes revealed that globin switches occurred in parallel with the erythropoietic transition. Colony-forming assays showed replacement of primitive clonogenic progenitor cells with definitive cells during culturing. A decline in embryonic zeta- and epsilon-globin expression at the translational level occurred in individual definitive erythroid progenitors. Expression of beta-globin in individual definitive erythroid progenitors was upregulated in the presence of OP9 stromal cells. Thus, this system reproduces early hematopoietic development in vitro and can serve as a model for analyzing the mechanisms of the globin switch in humans.

Animals↗

PubMed2005

Shot noise suppression in avalanche photodiodes.

We identify a new shot noise suppression mechanism in a thin (approximately 100 nm) heterostructure avalanche photodiode. In the low-gain regime the shot noise is suppressed due to temporal correlations within amplified current pulses. We demonstrate in a Monte Carlo simulation that the effective excess noise factors can be < 1, and reconcile the apparent conflict between theory and experiments. This shot noise suppression mechanism is independent of known mechanisms such as Coulomb interaction, or reflection at heterojunction interfaces.

Journal Article↗

PubMed2003

Tunica interna endothelial cell kinase expression and hematopoietic and angiogenic potentials in cord blood CD34+ cells.

Tunica interna endothelial cell kinase (TEK) is expressed in both hematopoietic and endothelial cells and plays a crucial role in hematopoiesis and angiogenesis in mouse development. In humans, however, little is known about the hematopoietic and angiogenic potentials of TEK-expressing cells in umbilical cord blood (CB) cells, which originate during the human fetal period. We therefore compared the hematopoietic and angiogenic abilities of CB CD34+TEK+ and CD34+TEK- cells by using a clonogenic assay and xenotransplantation into immunodeficient NOD/SCID mice. The results showed that colony-forming cells and cells capable of repopulating in NOD/SCID mice were present in both CD34+TEK+ and CD34+TEK- cells and that the hematopoietic activities of the cell types were similar. In contrast, the potential to differentiate into endothelial cells in vivo was greater in the CD34+TEK+ cells. All NOD/SCID mice engrafted with CD34+TEK+ cells had human CD31-expressing and VE-cadherin-expressing endothelial cells in the vessels of the ischemic muscles and/ or human endothelial cells expressing CD31, kinase-insert domain-containing receptor, and endothelial nitric oxide synthase in liver sinusoidal cells, whereas such endothelial cells were detected in only 3 of the 7 recipients engrafted with CD34+TEK- cells. This result has important implications in cell therapy using CB cells for treating hematopoietic disorders and vascular diseases.

Animals↗

PubMed2003

[Relations between trace elements in drinking water and elderly residents' cognitive function].

The relationship between trace element levels in drinking water and cognitive function was studied for elderly residents in rural areas in China. Cognitive function was measured by a Chinese translation of the Community Screening Interview for Dementia (CSI "D"). The trace elements fluoride, calcium, selenium, aluminum, iron, zinc, cadmium, lead and arsenic contents of drinking water were determined using Chinese. National Standard Methods. A mixed effects model was used to evaluate the effect of each of the elements on cognitive function while adjusting for age, sex, and education level. Several of the elements examined had a significant effect on cognitive function when they were examined in a univariate context. However, after adjusting for other elements many of these results were not significant. There was a significant quadratic effect for calcium and a significant zinc-cadmium interaction. Cognitive function increased with calcium level to a certain point, and then decreased as calcium continued to increase. Zinc showed a positive relationship with cognitive function at low cadmium levels, but a negative relationship at high cadmium levels.

Aged↗