42 research outputs found
Embryonal subregion-derived stromal cell lines from novel temperature-sensitive SV40 T antigen transgenic mice support hematopoiesis
Throughout life, the hematopoietic system requires a supportive
microenvironment that allows for the maintenance and differentiation of
hematopoietic stem cells (HSC). To understand the cellular interactions
and molecules that provide these functions, investigators have previously
established stromal cell lines from the late gestational stage and adult
murine hematopoietic microenvironments. However, the stromal cell
microenvironment that supports the emergence, expansion and maintenance of
HSCs during mid-gestational stages has been largely unexplored. Since
several tissues within the mouse embryo are known to harbor HSCs (i.e.
aortagonads-mesonephros, yolk sac, liver), we generated numerous stromal
cell clones from these mid-gestational sites. Owing to the limited cell
numbers, isolations were performed with tissues from transgenic embryos
containing the ts SV40 Tag gene (tsA58) under the transcriptional control
of constitutive and ubiquitously expressing promoters. We report here that
the growth and cloning efficiency of embryonic cells (with the exception
of the aorta) is increased in the presence of the tsA58 transgene.
Furthermore, our results show that the large panel of stromal clones
isolated from the different embryonal subregions exhibit heterogeneity in
their ability to promote murine and human hematopoietic differentiation.
Despite our findings of heterogeneity in hematopoietic growth factor gene
expression profiles, high-level expression of some factors may influence
hematopoietic differentiation. Interestingly, a few of these stromal
clones express a recently described chordin-like protein, which is an
inhibitor of bone morphogenic proteins and is preferentially expressed in
cells of the mesenchymal lineage
Using the past to constrain the future: how the palaeorecord can improve estimates of global warming
Climate sensitivity is defined as the change in global mean equilibrium
temperature after a doubling of atmospheric CO2 concentration and provides a
simple measure of global warming. An early estimate of climate sensitivity,
1.5-4.5{\deg}C, has changed little subsequently, including the latest
assessment by the Intergovernmental Panel on Climate Change.
The persistence of such large uncertainties in this simple measure casts
doubt on our understanding of the mechanisms of climate change and our ability
to predict the response of the climate system to future perturbations. This has
motivated continued attempts to constrain the range with climate data, alone or
in conjunction with models. The majority of studies use data from the
instrumental period (post-1850) but recent work has made use of information
about the large climate changes experienced in the geological past.
In this review, we first outline approaches that estimate climate sensitivity
using instrumental climate observations and then summarise attempts to use the
record of climate change on geological timescales. We examine the limitations
of these studies and suggest ways in which the power of the palaeoclimate
record could be better used to reduce uncertainties in our predictions of
climate sensitivity.Comment: The final, definitive version of this paper has been published in
Progress in Physical Geography, 31(5), 2007 by SAGE Publications Ltd, All
rights reserved. \c{opyright} 2007 Edwards, Crucifix and Harriso
MMN and Differential Waveform
A mismatch negativity response (MMN) and a new differential waveform were derived in an effort to evaluate a neural refractory or recovery effect in adult listeners. The MMN was elicited using oddball test runs in which the standard and deviant stimuli differed in frequency. To derive the differential waveform, the same standard and deviant stimuli were presented alone. MMN responses were obtained by subtracting the averaged responses to standards from the deviants. The differential waveforms were obtained by subtracting the averaged responses to standards presented alone from deviants presented alone. Scalp topography for the MMN and differential waveforms were similar. A significant (p < .05) positive and negative correlation was found between the earlier and later components of the bimodal MMN and the N1 and P2 component of the differential waveform, respectively. Further, N1 and P2 of the differential waveform were significant (p < .05) predictor variables of early and late peak amplitudes of the MMN. These results suggest that refractory effects may overlay/modify the morphology of the MMN waveform
Use of a constrain phage displayed-peptide library for the isolation of peptides binding to HIV-1 nucleocapsid protein (NCp7)
Ligament-Derived Matrix Stimulates a Ligamentous Phenotype in Human Adipose-Derived Stem Cells
Human adipose stem cells (hASCs) can differentiate into a variety of phenotypes. Native extracellular matrix (e.g., demineralized bone matrix or small intestinal submucosa) can influence the growth and differentiation of stem cells. The hypothesis of this study was that a novel ligament-derived matrix (LDM) would enhance expression of a ligamentous phenotype in hASCs compared to collagen gel alone. LDM prepared using phosphate-buffered saline or 0.1% peracetic acid was mixed with collagen gel (COL) and was evaluated for its ability to induce proliferation, differentiation, and extracellular matrix synthesis in hASCs over 28 days in culture at different seeding densities (0, 0.25 × 106, 1 × 106, or 2 × 106 hASC/mL). Biochemical and gene expression data were analyzed using analysis of variance. Fisher's least significant difference test was used to determine differences between treatments following analysis of variance. hASCs in either LDM or COL demonstrated changes in gene expression consistent with ligament development. hASCs cultured with LDM demonstrated more dsDNA content, sulfated-glycosaminoglycan accumulation, and type I and III collagen synthesis, and released more sulfated-glycosaminoglycan and collagen into the medium compared to hASCs in COL (p ≤ 0.05). Increased seeding density increased DNA content incrementally over 28 days in culture for LDM but not COL constructs (p ≤ 0.05). These findings suggest that LDM can stimulate a ligament phenotype by hASCs, and may provide a novel scaffold material for ligament engineering applications