progenitor cells

Examples of progenitor cells in the following topics:

• WBC Formation

  • Haematopoietic stem cells (HSCs) reside in the bone marrow and have the unique ability to give rise to all mature blood cell types through differentiation into other progenitor cells.
  • The daughters are the myeloid and lymphoid progenitor cells, which cannot self renew but differentiate into various myeloid leukocytes and lymphocytes respectively.
  • The lymphocyte lineage derives from common lymphoid progenitor cells, which in turn become lymphoblasts before differentiating into T cells, B cells, and NK cells.
  • Myelocytes are an offshoot of common myeloid progenitor cells, which also differentiate into the erythropoietic and magakaryotic progenitors.
  • Megakaryocytes (the cells that produce platelets) and erythrocytes (red blood cells) are not formally considered to be leukocytes, but arise from the common myeloid progenitor cells that produce the other cellular components of blood.

• Development of Blood and Blood Vessels

  • Endothelial stem cells (ESCs) are one of three types of stem cells found in bone marrow.
  • These parent stem cells, ESCs, give rise to endothelial progenitor cells (EPCs), which are intermediate stem cells that lose potency.
  • Progenitor stem cells are committed to differentiating along a particular cell developmental pathway.
  • The lineages arising from the EPC and the hematopoietic progenitor cell (HPC) form the blood circulatory system (see ).
  • Hematopoietic stem cells can of course undergo self-renewal, and are multipotent cells that give rise to erythrocytes (red blood cells), megakaryocytes/platelets, mast cells, T-lymphocytes, B-lymphocytes, dendritic cells, natural killer cells, monocyte/macrophage, and granulocytes.

• Platelet Formation

  • Platelets are small, clear, irregularly-shaped cell fragments produced by larger precursor cells called megakaryocytes.
  • Platelets are continuously produced as a component product of hematopoiesis (blood cell formation).
  • Thrombopoiesis occurs from common myeloid progenitor cells in the bone marrow, which differentiate into promegakaryocytes and then into megakaryocytes.
  • Thrombopoietin stimulates differentiation of myeloid progenitor cells into megakaryocytes and causes the release of platelets.
  • Myeloid progenitor cells differentiate into promegakaryocytes, and megakaryocytes, which release platelets.

• Medical Uses of Hematopoietic Growth Factors

  • Hemopoetic growth factors regulate the growth, differentiation, and proliferation of progenitor cells in the blood and bone marrow.
  • Hemopoietic growth factors regulate the differentiation and proliferation of particular progenitor cells.
  • Erythropoietin is a sialoglycoprotein hormone produced by peritubular cells of kidney.
  • G-CSF stimulates the production of white blood cells (WBC).
  • G-CSF is also used to increase the number of hematopoietic stem cells in the blood of the donor before collection by leukapheresis for use in hematopoietic stem cell transplantation.

• Development of Blood

  • The other daughters of HSCs, myeloid, and lymphoid progenitor cells, can each commit to any of the alternative differentiation pathways that lead to the production of one or more specific types of blood cells, but cannot self-renew.
  • Erythrocytes are oxygen-carrying red blood cells; they are derived from common myeloid progenitors.
  • Commonly known as white blood cells, they are derived from common lymphoid progenitors.
  • Erythropoietin is required for a myeloid progenitor cell to become an erythrocyte.
  • On the other hand, thrombopoietin makes myeloid progenitor cells differentiate to megakaryocytes, which produce platelets.

• Embryonic Development

  • The neural tube becomes patterned along the dorsal-ventral axis to establish defined compartments of neural progenitor cells, which will give rise to distinct classes of neurons.
  • These cell types are specified by the secretion of Shh from the notochord (located ventrally to the neural tube), and later from the floor plate cells.
  • The different combinations of expression of these transcription factors along the dorsal-ventral axis of the neural tube are responsible for creating the identity of the neuronal progenitor cells.
  • Five molecularly distinct groups of ventral neurons form from these neuronal progenitor cells in vitro.
  • Studies have shown that neural progenitors can evoke different responses based on the length of exposure to Shh, with a longer exposure time resulting in more ventral cell types.

• Muscle Development

  • The cells of the inner cell mass (embryoblast), which are known as human embryonic stem cells (hESCs), will differentiate to form four structures: the amnion, the yolk sac, the allantois, and the embryo itself.
  • Human embryonic stem cells are pluripotent; that is, they can differentiate into any of the cell types present in the adult human, and into any of the intermediate progenitor cell types that eventually turn into the adult cell lines. hESCs are also immortal: they can divide and grow in number indefinitely, without undergoing either differentiation or cellular aging (cellular senescence).
  • A myoblast is a type of embryonic progenitor cell that differentiates to give rise to muscle cells.
  • A myocyte (also known as a muscle cell or muscle fiber) is the type of cell found in muscle tissue.
  • Satellite cells are located between the basement membrane and sarcolemma (cell membrane) of individual muscle fibers.

• Development of the Immune System

  • This model of lymphopoiesis had the virtue of relative simplicity and agreement with nomenclature and terminology; also, it is essentially valid for the favorite lab animal, the mouse. pHSC pluripotent, self-renewing, hematopoietic stem cells give rise to MPP multipotent progenitors (these give rise to ELP, or PRO, Prolymphocytes); early lymphoid progenitors; and finally to the CLP Common lymphoid progenitor, a cell type fully committed to the lymphoid lineage. pHSC, MPP and ELP cells are not fully committed to the lymphoid lineage because if one is removed to a different location, it may differentiate into non-lymphoid progeny.
  • NK cells Dendritic cells (lymphoid lineage; DC2) Progenitor B cells Pro-B cells => Early Pro (or pre-pre)-B cells => Late Pro (or pre-pre)-B cells Large Pre-B cells => Small Pre-B cells Immature B cells B Cells => (B1 cells; B2 cells) Plasma cells Pro-T cells T-cells.
  • Antigen presenting cells in newborns have a reduced capability to activate T cells.
  • B cells develop early in gestation but are not fully active.
  • There is also some evidence that cell surface receptors on B cells and macrophages may detect sex hormones in the system.

• Natural Killer Cells

  • Natural killer cells (NK cells) are cytotoxic lymphocyte critical to the innate immune system.
  • The role of NK cells is similar to that of cytotoxic T cells in the adaptive immune response.
  • NK cells provide rapid responses to virally infected cells and respond to tumor formation by destroying abnormal and infected cells.
  • NK cells use two cytolytic granule mediated apoptosis to destroy abnormal and infected cells.
  • NK cells are large granular lymphocytes derived from the common lymphoid progenitor cells (lymphoblasts), which also generates B and T lymphocytes.

• Lymphoid Cells

  • The three major types of lymphocyte are T cells, B cells, and natural killer cells.
  • Therefore it acts as an inhibitor of NK cell activity, and NK cells will activate and destroy cells when it does not detect MHC class I on that cell surface.
  • Activated NK cells release cytotoxic (cell-killing) granules that contain perforin and granzyme, which can lyse cell membranes and induce apoptosis to kill infected or abnormal cells.
  • T cells are involved in cell-mediated immunity whereas B cells are primarily responsible for humoral immunity.
  • All lymphocytes originate, during this process, from a common lymphoid progenitor cell, known as a lymphoblast, before differentiating into their distinct lymphocyte types.