Role of Rictor in Hematopoietic Stem Cells during Fetal Liver Hematopoiesis

Abstract

To investigate the effect of Rictor on the hematopoiesis of fetal liver by specific knock-out of Rictor in hematopoietic cells of Vav-Cre mice. E12.5 0.08ee fetal liver cells from the experimental group Vav-Cre; Rictorf/f embryos and control group Rictor f/+ or Rictorf/f embryos were transplanted to recipients respectively to observe the effect of Rictor on reconstitution ability of hematopoietic stem cells. In the meantime, E14.5 0, 10, 20, 40, 60, 80 sorted hematopoietic stem cells from the Vav-Cre; Rictorf/f fetal liver of experimental group and Rictorf/+ or Rictorf/f fetal liver of control group were transplanted in to recipients to analyze the numbers of functional hematopoietic stem cells after Rictor was knocked-out. Furthermore, the self-renewal capacity was investigated by secondary transplantation of BM cells from primary recipients that had been successfully repopulated with E12.5 fetal liver-derived cells and by cell cycle analysis. All the recipients receiving E12.5 Rictorf/+ or Rictorf/f cells were repopulated (8/8, from 2 independent experiments) with an average chimerism of 77.2%±11.1% at 4 months post-transplantation, which resulted in 57 LT-RU per FL. In comparison, 8 out of 8 recipients receiving Vav-Cre; Rictorf/f cells were repopulated with significantly reduced chimerism (37.0%±16.3%) (P＜0.01), which was equivalent to 8 LT-RU per FL. The limiting dilution transplantation experiment showed that there was one functional hematopoietic stem cell out of 17 sorted SLAM cells in the control group, and one functional hematopoietic stem cell out of 39 sorted SLAM cells in the experimental group. The secondary transplantation experiments showed that 2 out of 4 recipients were reconstructed in the control group after 1 month, and 0 was reconstructed in the experimental group by transplanting 4×105 donor cells respectively. What＇s more, the percentage of S/G2/M cells in the experimental group increased when compared with controls. In the process of fetal liver hematopoiesis, the specifically knocking-out the Rictor in hematopoietic system can lead to defect of reconstitution ability, decrease of the functional hematopoietic stem cell numbers and reduction of self-renewal ability of hematopoietic stem cells.