Mouse hematopoietic stem-cell antigen Sca-1 is a member of the Ly-6 antigen family

Vascular smooth muscle differentiation of murine stroma: a sequential model

Previous studies by our group showed that stromal cells from human long-term marrow cultures were mesenchymal cells following a vascular smooth muscle pathway. The present study using 58 immortalized stromal lines from different hematopoietic sites was conducted to verify whether this hypothesis also held true for murine stroma. Principal components analysis performed using cytoskeletal and extracellular matrix proteins allowed the segregation of five factors explaining more than 70% of the variance. Factor I, including osteopontin and vimentin, and factor II, laminins and fibronectins, were representative of the mesenchyme. The remaining three factors were representative of vascular smooth muscle: factor III, including alphaSM actin, SM alpha actinin, SM22alpha, EDa+ fibronectin, and thrombospondin-1; factor IV, metavinculin and h-caldesmon; and factor V, smooth muscle myosin SM1 and desmin. All lines expressed factors I and II; 53 lines expressed factor III, 35 lines expressed factor IV; and 11 lines expressed factor V. A second principal components analysis including membrane antigens indicated the cosegregration of vascular cell adhesion molecule-1 with osteopontin and that of Ly6A/E with vimentin, whereas CD34 and Thy-1 appeared to be independent factors. The heterogeneity of vascular smooth muscle markers expression suggests that harmonious maintenance of hematopoiesis depends on the cooperation between different stromal cell clones.

Stem cell emergence and hemopoietic activity are incompatible in mouse intraembryonic sites

In the mouse embryo, the generation of candidate progenitors for long-lasting hemopoiesis has been reported in the paraaortic splanchnopleura (P-Sp)/ aorta-gonad-mesonephros (AGM) region. Here, we address the following question: can the P-Sp/AGM environment support hemopoietic differentiation as well as generate stem cells, and, conversely, are other sites where hemopoietic differentiation occurs capable of generating stem cells? Although P-Sp/AGM generates de novo hemopoietic stem cells between 9.5 and 12.5 days post coitus (dpc), we show here that it does not support hemopoietic differentiation. Among mesoderm-derived sites, spleen and omentum were shown to be colonized by exogenous cells in the same fashion as the fetal liver. Cells colonizing the spleen were multipotent and pursued their evolution to committed progenitors in this organ. In contrast, the omentum, which was colonized by lymphoid-committed progenitors that did not expand, cannot be considered as a hemopoietic organ. From these data, stem cell generation appears incompatible with hemopoietic activity. At the peak of hemopoietic progenitor production in the P-Sp/AGM, between 10.5 and 11.5 dpc, multipotent cells were found at the exceptional frequency of 1 out of 12 total cells and 1 out of 4 AA4.1+ cells. Thus, progenitors within this region constitute a pool of undifferentiated hemopoietic cells readily accessible for characterization.

Engraftment and multilineage expression of human bone marrow CD34- cells in vivo

The fetal sheep competitive engraftment model of human hematopoietic stem cells (HSC) was used to evaluate the in vivo engraftment potential of human bone marrow CD34- Lin- cells. Transplantation of CD34- Lin- cells into primary hosts resulted in the long-term (> 1 year) engraftment and multilineage donor cell/progenitor expression with production of significant numbers of CD34+ cells. Secondary transplantation and limiting dilution studies confirmed the presence in human CD34- fraction of HSC with in vivo long-term engraftment and multilineage differentiation potentials.

Thy-1 antigen expression by cells in the osteoblast lineage

Identification of surface markers involved in osteoblast differentiation provides a method to isolate osteoblasts at various stages of maturation. In this study, we examined expression of the T lymphocyte differentiation antigen, Thy-1, by osteoblastic cells from different species. Murine skeletal progenitor, neonatal calvarial, and adult bone cells (ABCs) were selected to represent osteoblasts at distinct stages of maturation. Flow cytometric analysis showed that Thy-1 expression was undetectable on the progenitor cells (mouse limb bud clones 14 and 17), appeared on calvarial cells (45%+), and was decreased on ABCs (< 10%+). Thy-1 was also detected in situ on osteoblastic cells in mouse calvariae. Thy-1 mRNA expression correlated with cell surface expression. Antigen expression was markedly increased during the cells' proliferative phase in culture. Furthermore, examination of primary rat and human osteoblast-like cells revealed that significant levels of Thy-1 were also expressed on those cells derived from subconfluent culture. This study indicates that osteoblasts express Thy-1 antigen and that its expression is maximal at their earliest stage of maturation, during the proliferative phase, and then declines as the cells mature. In a role similar to the one it plays in the hematopoietic system, Thy-1 antigen may be useful as a differentiation marker in following the development of the osteoblast.

Stimulation of Mouse and Human Primitive Hematopoiesis by Murine Embryonic Aorta-Gonad-Mesonephros–Derived Stromal Cell Lines

We report here on a novel stromal cell line, AGM-S3, derived from the aorta-gonad-mesonephros (AGM) region of a 10.5 days postcoitum (dpc) mouse embryo. The AGM-S3 cells promoted production of hematopoietic progenitors and day-12 spleen colony-forming cells from Lin−c-Kit+Sca-1+ murine primitive hematopoietic cells. They also supported for 6 weeks generation of human multipotential progenitors from cord blood CD34+CD38− primitive hematopoietic cells. Human long-term repopulating hematopoietic stem cells (LTR-HSC) with the potential to reconstitute hematopoiesis in NOD/SCID mice were maintained on AGM-S3 cells for at least 4 weeks. Flow cytometric analysis showed that CD13, vascular cellular adhesion molecule-1, and Sca-1 were expressed on AGM-S3 cells. Because stem cell factor, interleukin-6 (IL-6), and oncostatin M, but not IL-3, IL-11, leukemia- inhibitory factor, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, thrombopoietin, and Flk2 ligand were detected in reverse transcription-polymerase chain reaction analysis of AGM-S3 cells, the cells seem to express species-cross reactive molecule(s) other than the cytokines examined and which act on primitive hematopoietic progenitor/stem cells. This cell line is expected to elucidate molecular mechanisms regulating early hematopoiesis and pave the way for developing strategies for expansion of human transplantable HSC.

© 1998 by The American Society of Hematology.

Stimulation of Mouse and Human Primitive Hematopoiesis by Murine Embryonic Aorta-Gonad-Mesonephros–Derived Stromal Cell Lines

We report here on a novel stromal cell line, AGM-S3, derived from the aorta-gonad-mesonephros (AGM) region of a 10.5 days postcoitum (dpc) mouse embryo. The AGM-S3 cells promoted production of hematopoietic progenitors and day-12 spleen colony-forming cells from Lin−c-Kit+Sca-1+ murine primitive hematopoietic cells. They also supported for 6 weeks generation of human multipotential progenitors from cord blood CD34+CD38− primitive hematopoietic cells. Human long-term repopulating hematopoietic stem cells (LTR-HSC) with the potential to reconstitute hematopoiesis in NOD/SCID mice were maintained on AGM-S3 cells for at least 4 weeks. Flow cytometric analysis showed that CD13, vascular cellular adhesion molecule-1, and Sca-1 were expressed on AGM-S3 cells. Because stem cell factor, interleukin-6 (IL-6), and oncostatin M, but not IL-3, IL-11, leukemia- inhibitory factor, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, thrombopoietin, and Flk2 ligand were detected in reverse transcription-polymerase chain reaction analysis of AGM-S3 cells, the cells seem to express species-cross reactive molecule(s) other than the cytokines examined and which act on primitive hematopoietic progenitor/stem cells. This cell line is expected to elucidate molecular mechanisms regulating early hematopoiesis and pave the way for developing strategies for expansion of human transplantable HSC.

© 1998 by The American Society of Hematology.

A nestin-negative precursor cell from the adult mouse brain gives rise to neurons and glia

Using a novel suspension culture approach, previously undescribed populations of neural precursor cells have been isolated from the adult mouse brain. Recent studies have shown that neuronal and glial precursor cells proliferate within the subependymal zone of the lateral ventricle throughout life, and a persistent expression of developmentally regulated surface and extracellular matrix molecules implicates cell-cell and cell-substrate interactions in the proliferation, migration, and differentiation of these cells. By using reagents that may affect cell-cell interactions, dissociated adult brain yields two types of cell aggregates, type I and type II spheres. Both sphere types are proliferative, and type I spheres evolve into type II spheres. Neurons and glia arise from presumptive stem cells of type II spheres, and they can survive transplantation to the adult brain.

Altered proliferative response by T lymphocytes of Ly-6A (Sca-1) null mice

Ly-6A is a murine antigen which is implicated in lymphocyte activation and may be involved in activation of hematopoietic stem cells. Antibody cross-linking studies and antisense experiments have suggested that Ly-6A is a lymphocyte coactivation molecule. To better understand the function of Ly-6A, we used gene targeting to produce Ly-6A null mice which are healthy and have normal numbers and percentages of hematopoietic lineages. However, T lymphocytes from Ly-6A-deficient animals proliferate at a significantly higher rate in response to antigens and mitogens than wild-type littermates. In addition, Ly-6A mutant splenocytes generate more cytotoxic T lymphocytes compared to wild-type splenocytes when cocultured with alloantigen. This enhanced proliferation is not due to alterations in kinetics of response, sensitivity to stimulant concentration, or cytokine production by the T cell population, and is manifest in both in vivo and in vitro T cell responses. Moreover, T cells from Ly-6A-deficient animals exhibit a prolonged proliferative response to antigen stimulation, thereby suggesting that Ly-6A acts to downmodulate lymphocyte responses.

In vitro differentiation of embryonic stem cells: immunophenotypic analysis of cultured embryoid bodies

The process of in vitro embryonic stem cell differentiation and embryoid body development was monitored using a panel of antibodies against surface markers traditionally associated with embryonic tissue (Forssman, SSEA-1) and hematopoietic progenitor cells (Fall-3, HSA, Sca-1, Thy-1.2, ER-MP12, CD45, AA4.1, and c-kit). All markers with the exception of CD45 and AA4.1 were initially detected in cultures of undifferentiated ES cells. During the first 11 days of differentiation, distinct and reproducible patterns of surface expression were observed for each marker. Using the kinetic display of surface markers as a gauge of differentiation, perturbations in embryoid body development were detected in cultures supplemented with interleukin-11, a gp130-activating cytokine thought to affect embryonic stem cell differentiation. In the absence of exogenous cytokines, microbead immunoselected day 7 c-kit, ER-MP12, and CD45-positive embryoid body cells were enriched for hematopoietic progenitors as detected by methylcellulose colony assays, while no significant enrichment of hematopoietic progenitors was observed with Sca-1, Thy-1.2, Fall-3, and Forssman-immunoselected cells. These results indicate that the process of early embryoid body development is associated with a programmed sequence of cell surface marker display, concomitant with the development of phenotypically definable embryonic cell lineages.

Role of bcl-2 in the Development of Lymphoid Cells From the Hematopoietic Stem Cell

To investigate the role of bcl-2 in lymphohematopoiesis, a long-term bone marrow reconstitution system was established. Transplantation of 1,000 c-Kit+ Sca-1+ and lineage markers negative cells from bcl-2−/− mouse bone marrow resulted in long-term reconstitution of nonlymphoid cells. However, T cells were totally absent and B-lymphocyte development was severely impaired at a very early stage of differentiation in the chimeric mouse. On the other hand, transplantation of day 14 fetal liver cells from bcl-2−/− mice resulted in generation of both T and B cells in the recipient, albeit transiently. These data suggest that bcl-2 plays a critical role in the development of lymphoid progenitor cells from the hematopoietic stem cell (HSC), but is not essential for the development of nonlymphoid cells and the self-renewal of HSC. In addition, lymphopoiesis from fetal liver HSC appears to be less dependent on bcl-2 than adult bone marrow HSC.

Expression of the Ly-6E.1 (Sca-1) transgene in adult hematopoietic stem cells and the developing mouse embryo

The mouse hematopoietic marker Sca-1, encoded by the Ly-6E.1 and Ly-6A.2 genes, has been instrumental in the enrichment and characterization of the stem cell for the adult blood system. In the studies reported here, we use Ly-6E.1 genomic fragments to direct expression of a lacZ marker transgene in vivo to study Ly-6E.1 specific regulatory elements in the hematopoietic stem cell and to localize these cells in the developing mouse embryo. We demonstrate that a region approximately 9 kb downstream from the transcriptional start site is required for the distinct, restricted expression pattern of the Ly-6E.1-lacZ transgene within adult hematopoietic stem cells and embryos. We also demonstrate that viable and functional lacZ-expressing hematopoietic stem cells can be enriched by FDG staining and flow cytometric sorting. The Ly-6E.1-lacZ-mediated enrichment of hematopoietic stem cells from adult transgenic bone marrow in combination with the temporal expression pattern of the transgene in the pro/mesonephros suggest an intraembryonic site of development for these cells in the mouse.

In vitro differentiation of murine Sca-1+Lin- cells into myeloid, B cell and T cell lineages

Hematopoietic progenitor cells were shown to be capable of differentiating into myeloid, B cell and T cell lineages. We used a two-step culture system in which enriched murine hematopoietic progenitors in bone marrow were first plated in viscid culture medium containing methylcellulose, erythropoietin (EPO), stem cell factor (SCF) and interleukin (IL)-7. One thousand enriched murine marrow cells formed 53.5 +/- 12.1 (mean +/- SD) primary colonies. Cells from a single blast colony were separated into two aliquots and replated in secondary methylcellulose cultures containing SCF and IL-7 for B cell lineage and SCF, IL-3, G-CSF, GM-CSF and EPO for myeloid lineage. Next, cells from five to ten primary blast colonies were cultured again in embryonal thymus (25 Gy irradiated). One aliquot of blast colonies in a primary culture contained four colony forming units (CFU) of granulocytes, erythroblasts, macrophages and megakaryocytes, eight CFU-granulocytes and macrophages, and 28 BFU-E in a representative secondary myeloid culture. Another aliquot formed a few B cell colonies (2-10) in a secondary B cell culture. B lymphoid colonies were composed of blast-like cells with B-220 antigen. T cells in a secondary T cell culture consisted of 16% L3T4+, 16% CD8+ and 11% CD3+ of bone marrow origin in the thymus. From these results, we concluded that cells in the primary colonies from Sca-1+Lin- hematopoietic stem cells could differentiate into B cell, T cell and myeloid lineages.

Identification of a unique membrane-bound molecule on a hemopoietic stem cell line and on multipotent progenitor cells

Hemopoietic stem cells are a distinct population of cells that can differentiate into multilineages of hemopoietic cells and have long-term repopulation capability. A few membrane-bound molecules have been found to be preferentially, but not uniquely, present on the surface of these primitive cells. We report here the identification of a unique 105-kDa glycoprotein on the surface of hemopoietic stem cell line BL3. This molecule, recognized by the absorbed antiserum, is not present on the surface of myeloid progenitors 32D and FDC-P1 cells, EL4 T cells, and NIH 3T3 fibroblasts. This antiserum can also be used to block the proliferation of BL3 cells even in the presence of mitogen-stimulated spleen cell conditioned medium, which is known to have a stimulating activity on BL3 cells. It can also inhibit development of in vitro, fetal liver cell-derived multilineage colonies, but not other types of colonies, and of in vivo bone marrow cell-derived colony-forming unit spleen foci. These data suggest that gp105 plays an important role in hemopoietic stem cell differentiation.

Hematopoietic stem cell antigen-1 (Sca-1) expression in different lymphoid tissues of female mice treated with GnRH agonist

PROBLEM

Our earlier studies have demonstrated a general suppression of leukocyte maturation upon GnRH agonist treatment in mice and suggested a potential effect at an early stem cell stage of leukocyte development.

METHOD

Three-week old Balb/c and C57BL/6 female mice received 50 micrograms injections of Lupron depot or placebo. Sequential changes in Sca-1+ cells in the bone marrow, thymus, blood and spleen were studied by flow cytometry.

RESULTS

In bone marrow, the absolute numbers of Sca-1+ cells were significantly decreased at 2 weeks in C57BL/6 mice whereas a decreasing trend was noted in Balb/c mice following agonist administration. Concomitantly, thymocytes expressing Sca-1+ cells were significantly increased at 2 weeks in C57BL/6 mice, but were significantly decreased in Balb/c mice. Significant decreases in Sca-1+ cells were also observed in spleen and blood in Balb/c mice whereas no significant differences were observed in C57BL/6 mice.

CONCLUSIONS

These data suggest GnRH agonists affect hematopoietic stem cell development in mice. The effects observed vary with different genetic backgrounds. In Balb/c mice these effects are more pronounced, and appear to result in the inhibition of stem cell maturation. In contrast, GnRH agonist enhances stem cell maturation in C57BL/6 mice.

Tissue expression, structure and function of the murine Ly-6 family of molecules

Murine Ly-6 molecules are a family of cell surface glycoproteins which have interesting patterns of tissue expression during haematopoiesis from multipotential stem cells to lineage committed precursor cells, and on specific leucocyte subpopulations in the peripheral lymphoid tissues. These interesting patterns of tissue expression suggest an intimate association between the regulation of Ly-6 expression and the development and homeostasis of the immune system. Ly-6 molecules are low molecular weight phosphatidyl inositol anchored glycoproteins with remarkable amino acid homology throughout a distinctive cysteine rich protein domain that is associated predominantly with O-linked carbohydrate. These molecules are encoded by multiple tightly linked genes located on Chr. 15 which have conserved geneomic organization. The in vivo functions of Ly-6 molecules are not known although in vitro studies suggest a role in cellular activation. This review will summarize our understanding of Ly-6 with regard to tissue expression, molecular structure, gene organization and function.

Phenotypic analysis of murine long-term hemopoietic reconstituting cells quantitated competitively in vivo and comparison with more advanced colony-forming progeny

Early hemopoietic precursors have been extensively studied using short-term assays based on colony formation or in vivo reconstitution that do not run beyond a few weeks. However, little information is available on the phenotype of the stem cells that are detectable in 6-12-mo transplantation assays, and their relationship to cells detected in short-term assays is not known. In this study, we investigated the phenotype and separability by cell sorting of a spectrum of hemopoietic precursor cells in normal adult mouse marrow, including cells quantitated in a 1 yr competitive transplantation assay in vivo as well as in short-term colony assays in vitro and in vivo. Two principal findings emerged. The first was that cells detected in a variety of short-term assays--CFU-S12 (spleen colony-forming cells), CFCmulti (multilineage colony-forming cells), pre-CFCmulti (precursors of CFCmulti), CFC-E/Mg (erythroid/megakaryocyte CFC) and CFC-G/M (granulocyte/macrophage CFC)--were phenotypically similar and could not be separated from one another using a panel of markers useful in segregating them from more differentiated cells, including buoyant density, sedimentation velocity, adhesiveness to plastic, light scatter, high rhodamine-123 retention, and expression of surface wheat-germ agglutinin (WGA)-binding carbohydrate, H-2K, CD45, AA4.1, heat stable antigen (HSA), CD71, and Ly6A/Sca-1 antigens. Long-term reconstituting (LTR) cells quantitated in vivo differed little from the other precursors in expression of many of the above markers. However, they differed somewhat in lower sedimentation velocity and lower expression of WGA-binding surface carbohydrate, and most strikingly in their conditional adhesiveness to plastic, very low retention of Rh123 and high level expression of Ly6A/Sca-1, to a degree that would permit the quantitative separation of the two precursor classes from each other. The results provide a comprehensive characterization of LTR cells measured to 12 mo in vivo and a direct and quantitative analysis of their separation from cells detected in colony assays.

Murine B cell development: commitment and progression from multipotential progenitors to mature B lymphocytes

B lymphocytes, the cellular source of antibody, are critical components of the immune response. They develop from multipotential stem cells, progressively acquiring the traits that allow them to function as mature B lymphocytes. This developmental program is dependent on appropriate interactions with the surrounding environment. These interactions, mediated by cell-cell and cell-matrix interactions, provide the growth and differentiation signals that promote progression along the developmental pathway. This chapter addresses the properties of developing B lineage cells and the nature of the environmental signals that support B lineage progression.

An association between high Ly-6A/E expression on tumor cells and a highly malignant phenotype

Murine Ly-6 is a molecule expressed by various cells, including several types of hematopoietic cells such as pluripotent stem cells, and activated T cells. Ly-6 is also expressed on tumor cells originating from a variety of tissues. Preliminary observations suggested that the expression of Ly-6A/E is up-regulated on highly tumorigenic variants of polyoma-virus(PyV)-transformed BALB/c 3T3 cells as compared with weakly tumorigenic variants. On the basis of these observations, we sorted PyV-transformed A3C cells or DA3 mammary adenocarcinoma cells into stable sub-populations expressing high or low levels of membrane or mRNA Ly-6A/E. In vivo studies indicated that the high-Ly-6A/E-expressing cells in both tumor systems expressed a considerably more malignant phenotype (higher efficiency in local tumor production as well as in lung colonization) than low-Ly-6A/E expressors. Since the high-Ly-6A/E expressors did not exhibit any growth advantage in vitro over low Ly-6A/E expressors, we concluded that interactions of the former cells with micro-environmental factors operating in vivo (e.g., Ly-6A/E ligands) conferred upon these cells a highly malignant phenotype. Apart from the difference in Ly-6A/E expression, no other phenotypic characteristics distinguished highly from weakly malignant tumor cells. Similarly to T cells, where antibodies to Ly-6 transduce (or co-transduce) a proliferative signal, antibodies to Ly-6A/E were found to transduce a mitogenic signal to high-Ly-6A/E-expressing tumor cells but not to low-Ly-6A/E expressors. Taken together, these results show that Ly-6A/E expression is directly or indirectly associated in vivo with a highly malignant phenotype of 2 types of non-lymphoid murine tumors.

A novel marker of murine bone marrow hematopoietic stem cells that is expressed on peripheral T cells and is associated with a functionally important molecule on activated cytotoxic T lymphocytes

A MAb (R2/60) has been isolated that defines a novel lymphocyte marker of murine T cells. The determinant recognized by MAb R2/60 is present on a subset of bone marrow (BM) hematopoietic stem cells, on adult thymocytes, on peripheral T cells (both resting and activated), and on murine T cell tumor lines, although it is not expressed on mature B cells. In immunoprecipitation studies using radiolabeled membrane lysates from adult thymocytes, MAb R2/60 precipitated a 44-kDa membrane-bound dimer. Functionally, MAb R2/60 mediated antigen-independent cell lysis by activated CTLs, and by CTL clones, when bridged to Fc receptor-bearing target cells; however, binding of MAb R2/60 to effector cells prior to cytotoxic assays did not inhibit target cell lysis by CTLs, suggesting that the R2/60 determinant is involved in transmembrane signaling to already activated CTLs, but that it is not involved in target cell adhesion or antigen recognition. Moreover, direct stimulation of T cells by MAb R2/60 in the absence of additional stimuli did not induce cell proliferation, further implying that the R2/60 determinant is functionally involved in the effector rather than the inductive phase of the T cell response.

Bipotential precursors of B cells and macrophages in murine fetal liver

LYMPHOCYTES (B and T cells) derive continuously from the same multipotential stem cells that produce myeloid cells, including erythrocytes, granulocytes and macrophages. Tri- and bipotential myeloid intermediates between the multipotential stem cells and later unipotential cells have been identified using clonal methods in culture. Although similar methods have detected committed pre-B cells in mouse fetal liver, earlier progenitors with additional non-B lineage options have not been demonstrated in normal tissues. We report the characterization and purification of fetal liver cells that generate clones containing both macrophages and B cells, identified biochemically and morphologically. The common origin of the two cell types was shown by culture of single precursor cells. Their dual potential and unrearranged immunoglobulin loci place the precursors before exclusive B-lineage commitment in the haematopoietic hierarchy. The availability of such cells in purified form will allow direct study of lineage choice in cells having both lymphoid and non-lymphoid options.

Molecular analysis of the aberrant replication banding pattern on chromosome 15 in murine T-cell lymphomas

Cytogenetic techniques revealed an altered early replication banding pattern on the distal part of chromosome 15 in some murine T-cell lymphomas. This pattern reverted back to normal replication in somatic cell hybrids that had become non-tumorigenic after fusion of leukemic cells with normal fibroblasts. The altered banding pattern was correlated with malignancy. To investigate the molecular basis of the aberrant pattern in more detail, centrifugal elutriation of cells containing bromodeoxyuridine labeled DNA was used to prepare newly replicated DNA from selected intervals of the S-phase from tumor cells, as well as from hybrid cells with the revertant phenotype. These different DNA fractions were probed for DNA sequences distributed over the distal half of chromosome 15. Only two out of ten chromosome 15 specific genes tested showed a clear change in replication timing between the two different cell lines tested. These two genes were the lymphocyte antigen-6, Ly-6, and the neighboring thyroglobulin gene, Tgn, which replicated at the beginning of S in the tumor cells and later in S in the non-tumorigenic hybrid cells.

Hematopoietic development of embryonic stem cells in vitro: cytokine and receptor gene expression

A novel system to study early hematopoietic development is described. This report documents the in vitro capacity of murine embryonic stem (ES) cells to differentiate into hematopoietic precursors of most, if not all, of the colony-forming cells found in normal bone marrow. This system is used to correlate the genetic expression of cytokines, their receptors, the beta-globins, and the hematopoietic cell surface markers throughout the time course of ES cell differentiation with the hematopoietic development that occurs in these cultures. Our results indicate that there is a strong transcriptional activation, in a well-defined temporal order, of most of these genes including erythropoietin (Epo), CSF-1, IL-4, beta-globins, as well as the receptors for Epo, CSF-1, and IL-4. IL-3 and GM-CSF were not expressed during the first 24 days of ES cell differentiation. In contrast, the Steel (Sl) factor (SLF) was expressed early and underwent substantial up-regulation during this differentiation, and its receptor, c-kit, was expressed relatively constantly throughout the culture period. Our results are consistent with the conclusion that SLF, Epo, IL-4, and IL-6 are important during the early stages of ES cell differentiation and hematopoietic development. Furthermore, these results argue strongly that IL-3 and GM-CSF are not critical to early hematopoiesis. This system offers a unique in vitro model for studying hematopoietic development at the earliest possible stages.

Resolution and characterization of pro-B and pre-pro-B cell stages in normal mouse bone marrow

We have resolved B220+ IgM- B-lineage cells in mouse bone marrow into four fractions based on differential cell surface expression of determinants recognized by S7 (leukosialin, CD43), BP-1, and 30F1 (heat stable antigen). Functional differences among these fractions can be correlated with Ig gene rearrangement status. The largest fraction, lacking S7, consists of pre-B cells whereas the others, expressing S7, include B lineage cells before pre-B. These S7+ fractions, provisionally termed Fr. A, Fr. B, and Fr. C, can differentiate in a stromal layer culture system. Phenotypic alteration during such culture suggests an ordering of these stages from Fr. A to Fr. B to Fr. C and thence to S7- pre-B cells. Using polymerase chain reaction amplification with pairs of oligonucleotide primers for regions 5' of JH1, DFL16.1, and Jk1, we find that the Ig genes of Fr. A are in germline configuration, whereas Fr. B and C are pro-B cell stages with increasing D-J rearrangement, but no V-D-J. Finally, functional analysis demonstrates that the proliferative response to IL-7, an early B lineage growth factor, is restricted to S7+ stages and, furthermore, that an additional, cell contact-mediated signal is essential for survival of Fr. A.

Clonal analysis of hematopoietic stem-cell differentiation in vivo

Previous work has shown that the 0.02-0.05% of adult mouse bone marrow cells that bear the cell surface phenotype Thy-1loLin-Sca-1+ are enriched 1000- to 2000-fold for hematopoietic stem-cell activity in a variety of assays. When 50-100 cells of this phenotype are injected into an irradiated animal, they can permanently repopulate the entire hematopoietic system. In the present study, limiting-dilution and single-cell experiments were used to address the question of how individual Thy-1loLin-Sca-1+ stem cells contribute to repopulation of the hematopoietic system following irradiation. We calculated that 1 of 13 Thy-1loLin-Sca-1+ cells formed a clone comprising greater than 1% of peripheral white blood cells 3-7 weeks after injection. The majority of these clones included both lymphoid and myeloid lineages. Approximately one-third of the clones continued to produce new blood cells for 9 weeks or more, but the remainder disappeared earlier, including many that were multilineage. Thus, while the majority of Thy-1loLin-Sca-1+ bone marrow cells whose progeny are detected in the in vivo repopulation assay are pluripotential, only a subset undergo long-term self-renewal in vivo. Repopulation appears to be oligoclonal when limiting numbers of Thy-1loLin-Sca-1+ cells are injected. However, the number of clones contributing to hematopoiesis increases in proportion to the number of Thy-1loLin-Sca-1+ cells injected, bringing into question the notion that steady-state hematopoiesis in normal individuals is oligoclonal.

The glycosyl phosphatidylinositol anchor is critical for Ly-6A/E-mediated T cell activation

Ly-6E, a glycosyl phosphatidylinositol (GPI)-anchored murine alloantigen that can activate T cells upon antibody cross-linking, has been converted into an integral membrane protein by gene fusion. This fusion product, designated Ly-6EDb, was characterized in transiently transfected COS cells and demonstrated to be an integral cell surface membrane protein. Furthermore, the fusion antigen can be expressed on the surface of the BW5147 class "E" mutant cell line, which only expresses integral membrane proteins but not GPI-anchored proteins. The capability of this fusion antigen to activate T cells was examined by gene transfer studies in D10G4.1, a type 2 T cell helper clones. When transfected into D10 cells, the GPI-anchored Ly-6E antigen, as well as the endogenous GPI-anchored Ly-6A antigen, can initiate T cell activation upon antibody cross-linking. In contrast, the transmembrane anchored Ly-6EDb antigen was unable to mediate T cell activation. Our results demonstrate that the GPI-anchor is critical to Ly-6A/E-mediated T cell activation.

Characterization of promoter elements of an interferon-inducible Ly-6E/A differentiation antigen, which is expressed on activated T cells and hematopoietic stem cells

The Ly-6E/A antigen is expressed on activated murine T cells. Using probes made from the previously characterized cDNA, we have isolated a genomic DNA clone encoding the Ly-6A antigen. We determined the DNA sequence of the genomic clone and conducted a functional analysis of the promoter region. Mouse fibroblast BALB/3T3 cells transfected with this genomic clone constitutively expressed Ly-6A antigen on their cell surface. This expression was inducible by alpha/beta and gamma interferons. The Ly-6E 5'-flanking region was analyzed by chloramphenicol acetyltransferase assays in fibroblast cells for cis-acting elements. At least two positive elements were found to be needed for maximum constitutive promoter activity in L cells. One of the positive elements was specifically bound by a CCAAT box-binding protein from crude nuclear extract, as shown by electrophoretic mobility shift assays and footprinting. The other element, which contains a GGAAA motif and has homology to various known enhancers, also showed a specific binding activity. This second positive element when multimerized became a very powerful enhancing element. Interferon treatment could enhance expression of the chloramphenicol acetyltransferase gene fused to the Ly-6E 5'-flanking region in stably transfected BALB/3T3 cells. The elements responsible for this enhancement lie, at least in part, between positions -1760 and -900 of the gene. Surprisingly, there is no sequence homology between this region of Ly-6E and the established consensus for the interferon-stimulated response element, which has been shown functionally important to all previously characterized alpha/beta interferon-inducible promoters. The Ly-6E gene may prove to be a novel system for the study of interferon induction.

Resting and activated subsets of mouse multipotent hematopoietic stem cells

The fluorescent vital dye rhodamine 123 (Rh-123), which preferentially accumulates in mitochondrial membranes, can be used as a probe to indicate mitochondrial and hence cellular activity. In this study, mouse bone marrow hematopoietic stem cells were subdivided into Rh-123lo, Rh-123med, and Rh-123hi populations. The Rh-123lo (resting) population was significantly enriched in cells with a higher proliferative potential compared to the Rh-123hi (activated) population. The resting population exhibited a 20-fold greater ability to differentiate into splenic colony-forming units (CFU-S) relative to the activated population, whereas the activated population contained about 4-fold more day 13 CFU-S on primary transfer relative to the resting population. The two populations produced morphologically distinct splenic colonies; however, the frequency and morphology of in vitro colonies were very similar. Only the resting population provided sufficient stem cells to transfer long-term hematopoietic repopulation to secondary recipient animals after lethal irradiation. On a single cell level, the resting and activated populations exhibited an equivalent ability to differentiate into lymphoid and myeloid progeny. These observations provide further insight into the heterogeneous nature of CFU-S and directly demonstrate that multipotent hematopoietic stem cells are heterogeneous with regard to their clonogenic capacities.

Characterization of promoter elements of an interferon-inducible Ly-6E/A differentiation antigen, which is expressed on activated T cells and hematopoietic stem cells

The Ly-6E/A antigen is expressed on activated murine T cells. Using probes made from the previously characterized cDNA, we have isolated a genomic DNA clone encoding the Ly-6A antigen. We determined the DNA sequence of the genomic clone and conducted a functional analysis of the promoter region. Mouse fibroblast BALB/3T3 cells transfected with this genomic clone constitutively expressed Ly-6A antigen on their cell surface. This expression was inducible by alpha/beta and gamma interferons. The Ly-6E 5'-flanking region was analyzed by chloramphenicol acetyltransferase assays in fibroblast cells for cis-acting elements. At least two positive elements were found to be needed for maximum constitutive promoter activity in L cells. One of the positive elements was specifically bound by a CCAAT box-binding protein from crude nuclear extract, as shown by electrophoretic mobility shift assays and footprinting. The other element, which contains a GGAAA motif and has homology to various known enhancers, also showed a specific binding activity. This second positive element when multimerized became a very powerful enhancing element. Interferon treatment could enhance expression of the chloramphenicol acetyltransferase gene fused to the Ly-6E 5'-flanking region in stably transfected BALB/3T3 cells. The elements responsible for this enhancement lie, at least in part, between positions -1760 and -900 of the gene. Surprisingly, there is no sequence homology between this region of Ly-6E and the established consensus for the interferon-stimulated response element, which has been shown functionally important to all previously characterized alpha/beta interferon-inducible promoters. The Ly-6E gene may prove to be a novel system for the study of interferon induction.

T cell receptor-mediated negative selection of autoreactive T lymphocyte precursors occurs after commitment to the CD4 or CD8 lineages

To identify the maturational stage(s) during which T cell receptor (TCR)-mediated positive and negative selection occurs, we followed the development of CD4+8- and CD4-8+ T cells from TCRlo CD4+8+ thymic blasts in the presence of different positive and negative selecting (major histocompatibility complex or Mls) elements. We describe novel lineage-committed transitional intermediates that are TCRmed CD4+8lo or TCRmed CD4lo8+, and that show evidence of having been positively selected. Furthermore, negative selection is not evident until after cells have attained one of the TCRmed transitional phenotypes. Accordingly, we propose that negative selection in normal mice occurs only after TCRlo CD4+8+ precursors have been positively selected into either the CD4 or CD8 lineage.

Isolation and expression of the full-length cDNA encoding CD59 antigen of human lymphocytes

To identify the primary structure of CD59 antigen and to elucidate its function, a full-length cDNA clone of CD59 was isolated. The cDNA sequence contained an open reading frame that encodes an 128-amino-acid peptide. The amino-terminal 25 amino acids represented a typical signal peptide sequence and the carboxy-terminal hydrophobic amino acids were characteristic for phosphatidylinositol-anchored proteins. The predicted mature protein sequence showed 35% homology with murine Ly-6C.1 and 31% with Ly-6A.2. The number and the distribution of cysteine residues were conserved, implying that the CD59 represented a human homologue of murine Ly-6. RNA blot hybridization analysis revealed the expression of CD59 mRNA in placental, lung, and pancreatic tissues. The mRNA was not only expressed in T-cell lines but in some of monocytic, myeloid, and B-cell lines. In all of these tissues and cell lines, at least four mRNA species were detected. DNA blot hybridization analysis revealed a rather simple genomic structure, which suggested a single gene as compared with the complex multigene family of murine Ly-6.