Fig. 6: The spatial networks of the hematopoietic stem cell (HSC) populations.

We use a public dataset of spatial locations in the bone marrow consisting of HSC locations (source data²⁴) and proxy niche component locations (source data²⁵). In (A), color dots represent an example of the spatial locations of stem cells in the cell population, while the colors corresponds to the density of cells. We show an example of the spatial distribution of hematopoietic stem cells in the mouse tibia: the xy cross-section of the tibia with cells counted in a 260 μm × 350 μm area and the yz cross-section of the tibia with cells counted in a 350 μm × 11.5 μm area. Using these data, we build the resulting geometric random graphs (the cut-off radius of the illustration is set to 300 μm for illustration purposes). In (B, C), we use these networks to study evolutionary dynamics on these stem cell niche spatial networks as a function of their population size. The color dots use a cut-off distance of 15. Gray dots are results from other cut-off distances, ranging from 2 to 20, for comparison. The diaphysis is the shaft or central part of the tibia and the metaphysis is the neck portion of the bone (source data²⁵). Here, s = 0.01 and Ns varies with population size. B shows results using the Birth-death process and C shows the death-Birth process. Dots are averaged over at least 1 million simulations. The p values are obtained from a Wald test with a null hypothesis that the slope is equal to zero.