Abstract
ABSTRACT Some problems relating to the organisation of the haematopoietic stem cell pool may be approached by the analysis of changes in the patterns of mosaicism of X-chromosome linked products in the peripheral blood of female mice. We have used the A and B allozymes of the X-chromosome linked enzyme phosphoglycerate kinase (PGK-1) for this purpose. Estimates of the proportions of the two allozymes have been made in whole blood of female mice bled at intervals for up to two years, and also in granulocyte and lymphocyte populations purified on a fluorescence activated cell sorter. The intramouse variance in the proportions of PGK-1A and PGK-1B was shown to be low, indicating that many stem cells were contributing to haematopoiesis at any one time. In contrast the inter-mouse variance was relatively high, indicating that the founder number for the bone marrow compartment of the haematopoietic system was of the order of 20.
Highlights
Institut National de/a Santg et de/a Recherche Mgdicale U429, Hpita/ Nec/ber-Enfants Malades, Paris, France he development of immune defense mechanisms begins early during fetal life but is not completely achieved at birth, leading to a peculiar susceptibility of the neonate to infectious diseases. 1,z The earliest hematopoietic stem cells are detectable in the yolk sac around 6 weeks of gestation, but at that time they are only able to differentiate into myelomonocytic cells
Lymphoid cells with the surface phenotype of pro-T (CD7+) are found in the fetal liver by 7 weeks of gestation, and the fetal thymus is colonized by 8.5 weeks of gestation
Precursors of B cells are first detected in fetal liver at 8 weeks of gestation and thereafter in bonemarrow.The maturation of pre-B cells into mature B cells occur in these hematopoietic organs
Summary
Institut National de/a Santg et de/a Recherche Mgdicale U429, Hpita/ Nec/ber-Enfants Malades, Paris, France he development of immune defense mechanisms begins early during fetal life but is not completely achieved at birth, leading to a peculiar susceptibility of the neonate to infectious diseases. 1,z The earliest hematopoietic stem cells are detectable in the yolk sac around 6 weeks of gestation, but at that time they are only able to differentiate into myelomonocytic cells. Institut National de/a Santg et de/a Recherche Mgdicale U429, Hpita/ Nec/ber-Enfants Malades, Paris, France he development of immune defense mechanisms begins early during fetal life but is not completely achieved at birth, leading to a peculiar susceptibility of the neonate to infectious diseases. 1,z The earliest hematopoietic stem cells are detectable in the yolk sac around 6 weeks of gestation, but at that time they are only able to differentiate into myelomonocytic cells. Thereafter, the hematopoiesis takes place in the liver from the 7th week of gestation until the 6th month, thereafter in the bone-marrow. A unique precursor is at the origin of all hematopoitic cell lines
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