Beacham, G. M.; Ingram, Z. S.; Elrefaie, R. A.; Enkhbayar, K.; Zener, Z. R.; Affini, L.; Wasim, Z. N.; Dodge, M. C.; Sreerama, S.; Serrano, M. A.; Hagedorn, E. J.

Hematopoietic stem and progenitor cell (HSPC) niches support lifelong production of blood and immune cells. Recently, we identified a gene signature unique to HSPC niche endothelial cells that is highly conserved across species and developmental time, and includes the scavenger receptors, stab1/2 and mrc1a. Whether these receptors support HSPC development in the niche remains unclear. To investigate this, we used chemical inhibition and CRISPR mutagenesis in zebrafish and found that loss of stab2, and to a lesser degree stab1, reduced the number of embryonic HSPCs labeled by runx1:mCherry. Subsequent analyses of runx1:mCherry; cd41:GFP double transgenic embryos revealed an imbalance in the HSPC pool in stab2 mutants, with reductions in sub-populations containing stem cells and erythroid progenitors, the latter of which was most decreased. Our findings suggest stabilin scavenger receptors support HSPC development in the fetal niche, which could inform clinical strategies for culturing and expanding HSPCs.