Proliferation Of Normal Progenitor Cells Research Articles

The chromatin-remodeling protein ATRX is critical for neuronal survival during corticogenesis

Mutations in genes encoding chromatin-remodeling proteins, such as the ATRX gene, underlie a number of genetic disorders including several X-linked mental retardation syndromes; however, the role of these proteins in normal CNS development is unknown. Here, we used a conditional gene-targeting approach to inactivate Atrx, specifically in the forebrain of mice. Loss of ATRX protein caused widespread hypocellularity in the neocortex and hippocampus and a pronounced reduction in forebrain size. Neuronal “birthdating” confirmed that fewer neurons reached the superficial cortical layers, despite normal progenitor cell proliferation. The loss of cortical mass resulted from a 12-fold increase in neuronal apoptosis during early stages of corticogenesis in the mutant animals. Moreover, cortical progenitors isolated from Atrx-null mice undergo enhanced apoptosis upon differentiation. Taken together, our results indicate that ATRX is a critical mediator of cell survival during early neuronal differentiation. Thus, increased neuronal loss may contribute to the severe mental retardation observed in human patients.

The chromatin-remodeling protein ATRX is critical for neuronal survival during corticogenesis

Mutations in genes encoding chromatin-remodeling proteins, such as the ATRX gene, underlie a number of genetic disorders including several X-linked mental retardation syndromes; however, the role of these proteins in normal CNS development is unknown. Here, we used a conditional gene-targeting approach to inactivate Atrx, specifically in the forebrain of mice. Loss of ATRX protein caused widespread hypocellularity in the neocortex and hippocampus and a pronounced reduction in forebrain size. Neuronal "birthdating" confirmed that fewer neurons reached the superficial cortical layers, despite normal progenitor cell proliferation. The loss of cortical mass resulted from a 12-fold increase in neuronal apoptosis during early stages of corticogenesis in the mutant animals. Moreover, cortical progenitors isolated from Atrx-null mice undergo enhanced apoptosis upon differentiation. Taken together, our results indicate that ATRX is a critical mediator of cell survival during early neuronal differentiation. Thus, increased neuronal loss may contribute to the severe mental retardation observed in human patients.

Hypersensitivity of circulating progenitor cells to megakaryocyte growth and development factor (PEG-rHu MGDF) in essential thrombocythemia

Hematopoietic progenitor cells in 2 myeloproliferative disorders, juvenile chronic myelomonocytic leukemia and polycythemia vera, are known to be hypersensitive to cytokines that control normal progenitor cell proliferation, differentiation, and survival in their respective granulocyte/macrophage and erythroid lineages. Because thrombopoietin controls these functions in the normal megakaryocytic lineage, we asked the question: Are megakaryocytic progenitor cells in the myeloproliferative disorder essential thrombocythemia (ET) hypersensitive to thrombopoietin? Peripheral blood mononuclear cells from patients with ET, or secondary (reactive) thrombocytosis (2 degrees T), or healthy volunteers were grown in strictly serum-free agarose culture containing interleukin 3 (IL-3) and all-trans-retinoic acid, with various concentrations of PEG-rHu megakaryocyte growth and development factor (MGDF). The concentration of cytokine at half-maximum colony number served as a measure of progenitor cell sensitivity. Hypersensitivity to PEG-rHu MGDF was found in circulating progenitors from 18 of 20 (90%) informative patients with presumptive diagnosis ET, 1 of 8 (12.5%) 2 degrees T patients, and none of the 22 healthy volunteers. Median MGDF sensitivity ratio in ET patients was approximately 53 times greater than in the controls. This hypersensitivity, which was also directed to rHu thrombopoietin, was highly specific with respect to cytokine, disease, and cell lineage. We propose that, despite their single pluripotential cell origin, the different clinicopathologic phenotypes in different chronic myeloproliferative disorders are determined by lineage-restricted hypersensitivities of hematopoietic progenitor cells to endogenous cytokines. This work emphasizes the importance of stringent serum-free conditions for revealing true sensitivities to cytokines. The findings also offer a basis for evolving a positive test for ET, a diagnosis now made essentially by exclusion.

The effects of total saponins of panax ginseng on hematopoietic progenitor cells in healthy humans and aplastic anemia patients

Ginseng is said to have beneficial effects on anemia. The proliferation effects of total saponins of Panax ginseng (TSPG) on hematopoietic progenitor cell in healthy individuals and 29 patients with aplastic anemia (AA) were observed through bone marrow cultures of burst forming unit-erythroid (BFU-E), colony forming unit-erythroid (CFU-E) and colony forming unit-granulocyte/macrophage (CFU-GM) in vitro compared with methyltestosterone (MT). The results suggest TSPG might prompt the proliferation of normal progenitor cells at a concentration of 20 µg/ml. The numbers of BFU-E,CFU-E and CFU-GM increased by 37.8±2.9%, 31.4±2.9% and 33.3±4.0% respectively overthe controls; furthermore TSPG was still useful to BFU-E, CFU-E growth without Epo in vitro, although the colony numbers were much lower. Otherwise MT was useless to CFU-GM. Of the 29 patients with AA, 14 who responded to MT showed sensitivity to TSPG in marrow culture (the rising rate of colony formation exceeded 30%), but immune-mediated AA (patient’s peripheral blood mononucleated cell suppressed normal hematopoiesis) and stem cell decreased AA (few of colonies were formed) showed almost no expression for TSPG activity because of the immunological suppression system and the absence of progenitors.

Molecular cloning and expression of cDNA encoding a murine myeloid leukaemia inhibitory factor (LIF).

Leukaemia inhibitory factor (LIF) can induce macrophage differentiation in M1 murine myeloid leukaemic cells and suppress their proliferation in vitro. It does not stimulate the proliferation of normal progenitor cells and is apparently distinct from known colony-stimulating factors. We have used oligo-nucleotides complementary to partial amino acid sequence of LIF to isolate a LIF clone from a T lymphocyte cDNA library. When this cDNA was coupled to a yeast expression vector (YEpsec1) and introduced into yeast cells, a molecule with the biological properties characteristic of native LIF was secreted into the growth medium. The amino acid sequence of LIF established it to be a unique molecular entity, distinct from the other known haemopoietic growth factors. Since LIF is encoded by a unique gene, two biochemically separable forms of LIF probably represent post-transcriptional or posttranslational variants of the same gene product. In contrast to several other haemopoietic regulators, the 0.8- to 1-kb LIF mRNA was expressed constitutively in two murine T lymphocyte cell lines examined, and its abundance was not enhanced by stimulation with concanavalin A. Cloning, sequencing and expressing LIF has resolved several discrepancies in the literature concerning the identity of factors capable of inducing differentiation of murine myeloid leukaemic cells in vitro.

Acidic isoferritins as feedback regulators in normal and leukemic myelopoiesis.

The absence of normal hematopoiesis during acute leukemia not in remission and the recovery of apparently normal blood cells during chemotherapy-induced remission suggest that suppressive cell interactions may be involved in the pathogenesis of acute leukemia. Others have shown inhibition of normal progenitor cell proliferation and differentiation by cells from patients with leukemia, but little or no information was provided regarding the actual characterization of the inhibitory cells or the mechanisms of action (Broxmeyer and Moore 1978). We have demonstrated the existence of an S-phase specific inhibitory activity [leukemia-associated inhibitory activity (LIA)] against normal granulocyte-macrophage progenitor cells (CFU-GM) which was produced by bone marrow, spleen, and blood cells from patients with acute and chronic myeloid and lymphoid leukemia and “preleukemia” (Broxmeyer et al. 1978a,b, 1979a,b). Greater concentrations of LIA were found during acute leukemia (newly diagnosed and untreated, or on therapy but not in remission) than during chronic leukemia (Broxmeyer et al. 1978a,b). Remission of acute leukemia was associated with low levels of LIA (Broxmeyer et al. 1978b, 1979a), and LIA at that time was not found in hemopoietic cells from normal donors (Broxmeyer et al. 1978a,b, 1979a,b). In contrast to its action on normal CFU-GM, LIA was not effective in suppressing the growth of normal CFU-GM from patients with acute leukemia who were not in remission and from many patients with acute leukemia during remission and with chronic leukemia (Broxmeyer et al. 1978b, 1979a,b). We postulated that LIA may thus confer a proliferative advantage to abnormally responsive cells (Broxmeyer et al. 1978b).