Relation of Blood Cells to Connective Tissues and Endothelium

Regulation of Erythropoiesis. XV. Neonatal Erythropoiesis and the Effect of Nephrectomy *

“…In the newborn rat erythropoiesis is normoblastic and appears to develop from a primitive syn-cytial type of stem cell similar to that described in fetal hematopoietic tissues of the human (24). At about the fifteenth day, the numbers of these cells decrease and are no longer present after the fortieth day; instead there are individual cells, which one might classify as reticulum cells.…”

“…In support of such a view is the fact that in the human embryo at about 5 months the liver has primarily erythropoiesis and the marrow has leukopoiesis; later the marrow begins to support hematopoiesis entirely (25). Not only does an analogous situation obtain during the first week of life in the rat, but the morphology of the "stem cell" and the degree of macrocytosis at this stage of human fetal development are similar to those seen in the newborn rat (24). If so, then a "fetal" type of cell production might be anticipated in the rat even after birth with the production of fetal rather than adult type hemoglobin.…”

Clonal analysis identifies hemogenic endothelium as the source of the blood-endothelial common lineage in the mouse embryo

“…Precursors of the extra-embryonic mesoderm are located in the proximal epiblast and are the earliest to migrate though the streak. 2 As early as 1874, histologic analysis led Ranvier (as cited by Maximow 3 ) to propose that hemangioblasts in the early extra-embryonic mesoderm generate both blood and endothelial cells in the mammalian YS blood islands. Studies in chicks also suggested direct lineage relationships between blood and endothelial cells.…”

“…In parallel with the hemangioblast hypothesis, other pioneering histologic analyses instigated the idea of the hemogenic endothelium, 3 which has been demonstrated in vitro 11,12 and in the large embryonic vessels of a chick, mouse, and fish. [13][14][15] In addition, endothelial cells with hematopoietic potential have also been described in the YS of the mouse embryo.…”

Introduction: spatial origin of murine hematopoietic stem cells

“…The "mother" stem cell was identifiable as a mononuclear cell with a large nucleus, prominent nucleoli and deeply basophilic staining cytoplasm. [7][8][9] This cell was present in every tissue displaying hematopoietic activity, leading Maximow 8 and Danchakoff 7 to hypothesize that the stem cell must arise independently in each hematopoietic tissue at a specific time or under specific circumstances. Seventy-five years later, the fetal liver has clearly been established as the site of development for HSCs that seed the bone marrow compartment; 6,10 however, the temporal and spatial origin of the HSCs that seed the fetal liver remains controversial.…”