2 research outputs found
The role of apoptosis in the development of AGM hematopoietic stem cells revealed by Bcl-2 overexpression
Apoptosis is an essential process in embryonic tissue remodeling and adult
tissue homeostasis. Within the adult hematopoietic system, it allows for
tight regulation of hematopoietic cell subsets. Previously, it was shown
that B-cell leukemia 2 (Bcl-2) overexpression in the adult increases the
viability and activity of hematopoietic cells under normal and/or
stressful conditions. However, a role for apoptosis in the embryonic
hematopoietic system has not yet been established. Since the first
hematopoietic stem cells (HSCs) are generated within the
aortagonad-mesonephros (AGM; an actively remodeling tissue) region
beginning at embryonic day 10.5, we examined this tissue for expression of
apoptosis-related genes and ongoing apoptosis. Here, we show expression of
several proapoptotic and antiapoptotic genes in the AGM. We also generated
transgenic mice overexpressing Bcl-2 under the control of the
transcriptional regulatory elements of the HSC marker stem cell antigen-1
(Sca-1), to test for the role of cell survival in the regulation of AGM
HSCs. We provide evidence for increased numbers and viability of Sca-1(+)
cells in the AGM and subdissected midgestation aortas, the site where HSCs
are localized. Most important, our in vivo transplantation data show that
Bcl-2 overexpression increases AGM and fetal liver HSC activity, strongly
suggesting that apoptosis plays a role in HSC development
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