The sinusoidal hematopoietic niche is formed by Jam1a via Notch signaling in the zebrafish kidney

The zebrafish is a unique model to understand hematopoietic niches as hematopoietic stem/progenitor cells are maintained in the kidney. However, little is known about which cell types in the kidney play a role in hematopoietic niches. Here, we demonstrate that the sinusoidal endothelium is an essential and conserved niche component in the zebrafish kidney. Histological analysis revealed that runx1:mCherry(+) hematopoietic cells were predominantly detected in the dorsolateral region of the kidney where sinusoids are highly developed. Loss of Junctional adhesion molecule 1a (Jam1a), which is expressed in both sinusoidal endothelial cells and hematopoietic cells, resulted in a remarkable reduction in sinusoids and a defect in hematopoietic niches. We found that Jam1a regulates jagged-1a expression in vascular endothelial cells to form a sinusoidal structure in the kidney. Collectively, these data suggest that sinusoids are formed by Jam1a via endothelial Notch signaling to provide hematopoietic niches in the zebrafish kidney.