ch 20 pt 3

• what are the two waves that occur during vertebrate hematopoiesis

  primitive wave and definitive wave
• description of primitive wave:


  primitive wave- predominantly produces erythrocytes as well as some primitive macrophages. found in extraembryonic yolk sac where early erythrocytes are generated. occurs in inner cell mass and RBI
• description of definitive wave:


  provides the organism with long term HSCs capable of unlimited self renewal and able to generate all mature hematopoietic lineages. found in AGM, later transitioning to the mammalian fetal liver and the bone marrow
• hemotopoiesis and what does it produce?


  the generation of blood cells and produces more stem cells and progenitor cells that can respond to the environment around them to differentiate into about a dozen mature blood cell types
• what is the critical stem cell in hematopoiesis? what does it do and how does it do it?


  pluripotent hematopoietic stem cell; capable of producing all the blood cells and lymphocytes of the body by generating a series of intermediate progenitor cells whos potency is restricted to certain lineages
• all hematopoietic stem cells are derived from where?

  from cells originating in the extra embryonic blood islands surrounding the yolk sac
• what was novel about where the hematopoietic stem cells derive from?


  they thought that the cells were coming from the ventral endothelium; what was novel was that there was an intermediate region between the blood islands and bone marrow
• what are the sites of adult hematopoiesis in mice?


  spleen and bone marrow
• experiments using chicks, quails, and mice which suggested that hematopoiesis was restricted to the ventral portion of the aorta?


  early chick yolk sacs were transplanted onto 2-day quail embryos. They indicated that all blood cells of the late quail embryo originated from the quail host not from the transplanted chick yolk sac

  grafting of splanchnopleure from AGM region from one genetically variant mouse to another confirmed that in mammals, too, definitive hematopoiesis takes place from inside the embryo
• what is a hemogenic endothelial cell?


  primary endothelial cells of the dorsal aorta, in the ventral area, derived from the lateral plate. they give rise to hematopoietic stem cells
• what does gene/protein runx1 do?


  the transition from endothelial cell to hematopoietic stem cell was mediated by activation of the runx1 transcription factor
• what happens when runx1 is absent in mice?


  blood stems failed to form in the yolk sac, umbilical arteries, dorsal aorta, and placental vessels
• what is meant by "shear force"?

  like friction (to activate the runx1 gene in the ventral endothelium of the dorsal aorta)
• what is the role of nitric oxide in hematopoiesis?


  activates runx1 and other genes known to be critical for blood cell formation
• why is bone marrow HSC "remarkable"? experimentally how is this known?

  it's the common precursor of red blood cells, white blood cells, monocytes, and lymphocytes. when transplanted into inbred, irradiated mice HSCs can repopulate in the host mouse with all the blood and lymphoid cell types
• maintenance of the HSC depends on what?

  stem cell niche & ability of the HSC to receive the paracrine factor stem cell factor
• describe the experiments that helped determine which cells of the stem cell niche were supplying SCF

  they constructed genetically recombined mice in which the gene for SCF was replaced by the gene for green fluorescent protein in all or in selected cell types

  fewer HSC survived in either the endothelial cells or the perivascular cells (SCF needed for the HSC survival is made primarily by the perivascular cells with some contribution from the endothelial cells
• what is erythropoietin?


  a hormone that acts on erythroid progenitor cells to produce proerythroblasts which will generate red blood cells
• why do some athletes illegally use erythropoietin?


  it creates more red blood cells that in turn carry oxygen to their muscles
• what are cytokines?


  paracrine factors involved in blood cell and lymphocyte formation
• the developmental path taken by a descendant of a pluripotent HSC depends on what

  depends on which growth factor it meets and therefore determined by the stromal cells
• what are hematopoietic inductive microenvironments?


  cell regions that induce different sets of transcription factors in multipotent hematopoietic stem cells; these transcription factors specify the developmental path taken by descendants of those cells