Biomedical subjects

C T Jordan

Publications and source records attributed to C T Jordan.

25 records · Page 2Linked to original sources

PubMed1995

Long-term repopulating abilities of enriched fetal liver stem cells measured by competitive repopulation.

To characterize hematopoietic cell biology, many investigators have used protocols that enrich for primitive hematopoietic stem cells (PHSC). In this study, we quantified the long-term repopulating ability (LTRA) of enriched and discarded fractions of PHSC from day-14 murine fetal liver using the competitive repopulation assay. We fractionated populations of fetal cells using the antigenic markers AA4.1+, AA4.1+/Sca+, and AA4.1+/Linlow/Sca+. Differentiating and repopulating abilities of each of these populations were directly compared using competitive repopulation. Adult bone marrow was mixed with fetal cell fractions from congenic donors having genetically distinguishable markers, and mixtures were given to irradiated recipients. Differentiating and repopulating abilities of the enriched donor cells were measured by the proportions of myeloid and lymphoid cells having donor markers that repopulated the recipients. LTRA was found primarily in the AA4.1+ and AA4.1+/Sca+ subpopulations. Further fractionation of the AA4.1+ cells to derive an AA4.1+/Linlow/Sca+ fraction showed that virtually all of the long-term stem cell activity was found in this subpopulation. These cells were 1400- to 1600-fold enriched in long-term functional ability compared to fresh marrow. This very high multilineage repopulating ability per cell was directly measured using a long-term functional assay in vivo. Importantly, the measured repopulating ability for AA4.1+/Linlow/Sca+ cells was about five-fold less than expected from the fraction of cells enriched and remained two- to three-fold less even after compensating for repopulating ability in discarded fractions. This illustrates that long-term functional abilities of enriched PHSC cannot be estimated from fractions enriched but should be quantitatively assayed.

Aging↗

PubMed1994

Cellular and molecular characterization of the role of the flk-2/flt-3 receptor tyrosine kinase in hematopoietic stem cells.

The flk-2/flt-3 receptor tyrosine kinase was cloned from a hematopoietic stem cell population and is considered to play a potential role in the developmental fate of the stem cell. Using antibodies derived against the extracellular domain of the receptor, we show that stem cells from both murine fetal liver and bone marrow can express flk-2/flt-3. However, in both these tissues, there are stem cell populations that do not express the receptor. Cell cycle analysis shows that stem cells that do not express the receptor have a greater percentage of the population in G0 when compared with the flk-2/flt-3-positive population. Development of agonist antibodies to the receptor shows a proliferative role for the receptor in stem cell populations. Stimulation with an agonist antibody gives rise to an expansion of both myeloid and lymphoid cells and this effect is enhanced by the addition of kit ligand. These studies serve to further illustrate the importance of the flk-2/flt-3 receptor in the regulation of the hematopoietic stem cell.

Animals↗

PubMed1993

Primitive hemopoietic stem cells: direct assay of most productive populations by competitive repopulation with simple binomial, correlation and covariance calculations.

Quantitative analyses of primitive hemopoietic stem cell (PHSC) populations are important both for basic biology and for clinical applications. Unfortunately, many conventional assays fail to measure long-term repopulating ability and maximal differentiating ability, the most important characteristics of the PHSC. The competitive repopulation assay described here focuses on this characteristic, assaying the precursors from which most differentiated cells are descended over large fractions of the life span in laboratory mice. Thus long-term repopulating ability and the ability to differentiate into both myeloid and lymphoid lineages are measured directly from 2.5 to 12.5 months after transplantation. This technique also has found high correlations between granulocytes, macrophages, and T and B lymphocytes as early as 3 weeks after transplantation. All or most differentiated cells of these widely disparate types appear to be descended from a common precursor cell, while myeloid-specific or lymphoid-specific precursors produce few or no descendants. However, large increases in variances between 3 and 6 weeks and 12 weeks after transplantation suggest that most of the initially active multilineage precursors are exhausted. Thus the ability to differentiate into widely disparate lineages does not establish long-term repopulating ability.

Animals↗

PubMed1991

A receptor tyrosine kinase cDNA isolated from a population of enriched primitive hematopoietic cells and exhibiting close genetic linkage to c-kit.

We have cloned a receptor tyrosine kinase cDNA, designated fetal liver kinase 1 (Flk-1), from mouse cell populations enriched for hematopoietic stem and progenitor cells. Sequence analysis of this clone reveals strong homology to the c-Kit subfamily of receptor kinases, and in particular to the Flt gene product. Chromosomal mapping shows that the Flk-1, Kit, and Pdgfra genes are closely linked. Flk-1 mRNA is expressed in primitive and more mature hematopoietic cells as well as in a wide variety of nonhematopoietic tissues.

Amino Acid Sequence↗

PubMed1991

A receptor tyrosine kinase specific to hematopoietic stem and progenitor cell-enriched populations.

To elucidate the molecular biology of the hematopoietic stem cell, we have begun to isolate genes from murine cell populations enriched in stem cell activity. One such cDNA encodes a novel receptor tyrosine kinase, designated fetal liver kinase-2 or flk-2, which is related to the W locus gene product c-kit. Expression analyses suggest an extremely restricted distribution of flk-2. It is expressed in populations enriched for stem cells and primitive uncommitted progenitors, and is absent in populations containing more mature cells. Therefore, this receptor may be a key signal transducing component in the totipotent hematopoietic stem cell and its immediate self-renewing progeny.

Amino Acid Sequence↗

PubMed1990

Cellular and developmental properties of fetal hematopoietic stem cells.

We have characterized the fetal totipotent hematopoietic stem cell using a novel strategy that integrates physical analysis of cell properties and genetic analysis of in vivo developmental behavior. This approach allows the simultaneous isolation and in vivo characterization of any stem cell population. Using this procedure we demonstrate that a cell surface marker, recognized by monoclonal antibody AA4.1, defines 0.5%-1.0% of fetal liver tissue that contains the entire hierarchy of primitive hematopoietic cells. The AA4.1+ subpopulation includes multipotential in vitro progenitors, CFU-S cells, and lymphoid-myeloid stem cells that function to yield permanent and oligoclonal blood systems. Further fractionation of these cells by analysis of density, fibronectin binding, and surface antigen distribution has defined 0.1%-0.2% of fetal liver that contains the totipotent stem cell.

Animals↗

PubMed1990

Clonal and systemic analysis of long-term hematopoiesis in the mouse.

We have analyzed the temporal in vivo fate of 142 individual stem cell clones in 63 reconstituted mice. Long-term sequential analyses of the four major peripheral blood lineages, obtained from animals engrafted with genetically marked stem cells, indicate that developmental behavior is primarily a function of time. As such, the first 4-6 months post-engraftment is characterized by frequent fluctuations in stem cell proliferation and differentiation behavior. Gradually, a stable hematopoietic system emerges, dominated by a small number of totipotent clones. We demonstrate that single stem cell clones are sufficient to maintain hematopoiesis over the lifetime of an animal and suggest that mono- or oligoclonality may be a hallmark of long-term reconstituted systems. A model is proposed, wherein lineage-restricted differentiation and dramatic clonal flux are consequences of mechanisms acting on an expanding pool of totipotent cells and are not indicative of intrinsically distinct stem cell classes.

Animals↗