Kit ligand has a critical role in mouse yolk sac and aorta-gonad-mesonephros hematopoiesis (2018)
Figure 5

Figure 5. Kitl is required for AGM (pre-) HSC maturation and survival in vivo

A. Confocal whole-mount immunofluorescence analysis (WM-IF) of Kit+ cells in wild type and Sl/Sl E10.5 AGM (32-36sp). Images are 3D projections from 400μm-thick Z stacks, and are representative of 14 wild type and 11 Sl/Sl embryos analyzed. Total numbers of Kit+ cells (white) in the dorsal aorta were quantified and showed a significant reduction in Sl/Sl compared to wild type (p=0.008). CD31+ vasculature is shown in green. Arrowheads: hematopoietic cell clusters. Scale bars: 100μm.

B: Quantification of WM-IF in (A), showing absolute numbers (±SD) of clusters of indicated size and separately shown relative to location. A total of 7 wild type and 7 Sl/Sl embryos were counted.

C. Flow cytometry analysis of the HSC lineage in wild type and Sl/Sl E11.5 AGM+VU. Cells were Ter119- VE-Cadherin+ Kit+ gated and percentages of cells within the pre-HSC type I gate (red) and the pre-HSC type II/HSC gate (green) are shown. Percentages are the mean (±SD) of 10 wild type and 9 Sl/Sl biological replicates, with each replicate consisting of 1-3 pooled AGM+VU. A total of 15 wild type and 11 Sl/Sl embryos were analyzed over 5 independent experiments.

D. Absolute numbers (±SD) of E10.5 and E11.5 pre-HSC type I (Ter119- VE-Cadherin+ Kit+ CD41+ CD45-) and pre-HSC type II/HSC (Ter119- VE-Cadherin+ Kit+ CD41+ CD45+), as determined by flow cytometry in (C). Number of E11.5 embryos analyzed: as in (A). For E10.5, 5 biological replicates were analyzed for either genotype, with each replicate consisting of 1-4 pooled AGM+VU. A total of 12 wild type (31-35sp) and 9 Sl/Sl (30-34sp) embryos were analyzed over 4 independent experiments. Total live cells per AGM+VU: 2.8±1.0x105 (wt), 2.3±0.6x105 (Sl/Sl) at E10.5; 3.9±1.1x105 (wt), 3.8±1.4x105 (Sl/Sl) at E11.5.

E. CFU-C numbers per wild type and Sl/Sl E11.5 AGM+VU. Counts are the mean (±SD) of 4 wild type and 6 Sl/Sl biological replicates plated in duplicate. Biological replicates consisted of cells from individual or 2 pooled AGM+VU. A total of 6 wild type and 7 Sl/Sl AGM+VU embryos were analyzed over 4 independent experiments. GEMM: granulocyte, erythroid, monocyte/macrophage, megakaryocyte; G/M/GM: granulocyte, monocyte/macrophage; Ery: erythroid.

F. Analysis of long-term multi-lineage HSC potential in E11.5 Sl/Sl AGM+VU. Irradiated CD45.1 syngeneic mice were transplanted with 1 e.e. of wild type, Sl/+ or Sl/Sl CD45.2+ AGM+VU cells. PB chimerism is represented as the percentage of donor CD45.2+ cells among total CD45+ cells, 16 weeks after transplant. A total of 14 recipients were transplanted with wild type or Sl/+ cells and 8 with Sl/Sl cells, over 4 independent experiments. Wild type is represented with a circle, Sl/+ a triangle and Sl/Sl with a square. Tail somite range: 9-17 (+/+, Sl/+); 10-17 (Sl/Sl). *:p=0.027, one-tailed Mann-Whitney's U test; p=0.055, two-tailed Mann-Whitney's U test.

G. Confocal WM-IF analysis of pHH3 expression in Kit+ cells of wild type and Sl/Sl E10.5 dorsal aorta (33-36sp). Images are 2.5μm-thick single longitudinal Z slices; dorsal up. Arrowheads indicate examples of proliferating CD31+ pHH3+ Kit+ hematopoietic cells (magnified in insets); the total number of these cells per dorsal aorta was quantified and showed reduced proliferation in the mutant (p=0.01). A total of 4 embryos per genotype were analyzed. Scale bars: 50μm.

H. Confocal WM-IF analysis of cCasp3 expression in Kit+ cells of wild type and Sl/Sl E10.5 dorsal aorta (33-36sp). 2.5μm-thick single longitudinal Z slices; dorsal up. A higher number of Kit+ cCasp3+ apoptotic cluster cells were detected in the Sl/Sl dorsal aorta (p=0.04). Arrowheads indicate a CD31+ Kit+ cCasp3- hematopoietic cluster for wild type and an apoptotic CD31+ Kit+ cCasp3+ hematopoietic cell for Sl/Sl (both magnified in insets). A total of 4 wild type and 3 Sl/Sl embryos were analyzed. Scale bars: 50μm.

I. Analysis of apoptosis among pre-HSC type II/HSCs freshly isolated from wild type and Sl/Sl E11.5 AGM. Ter119- VE-Cadherin+ Kit+ CD41+ CD45+ cells were analyzed by flow cytometry for Annexin V binding to detect early apoptotic cells. Percentages are the mean (±SD) of 9 wild type and 7 Sl/Sl biological replicates analyzed over 3 independent experiments. Individual replicates consisted of 1-3 AGMs. A total of 13 wild type and 9 Sl/Sl embryos (11-17 tail sp) were analyzed. The percentage of apoptotic pre-HSC type II/HSCs in the mutant AGM was significantly increased.

J. Multiplex Fluidigm qRT-PCR analysis of pre-HSC type I and II, sorted as shown in (C) from E11.5 wild type (n=4 biological replicates; total number of embryos: 9; 11-17 tail somites) and Sl/Sl (n=5 biological replicates; total number of embryos: 9; 11-17 tail somites). Data are mean (±SD).

Data information: *P<0.05 (Unpaired two-tailed Student t-test).