Enrichment of hematopoietic stem/progenitor cells in the zebrafish kidney.

Hematopoietic stem cells (HSCs) maintain the entire blood system throughout life and are utilized in therapeutic approaches for blood diseases. Prospective isolation of highly purified HSCs is crucial to understand the molecular mechanisms underlying regulation of HSCs. The zebrafish is an elegant genetic model for the study of hematopoiesis due to its many unique advantages. It has not yet been possible, however, to purify HSCs in adult zebrafish due to a lack of specific HSC markers. Here we show the enrichment of zebrafish HSCs by a combination of two HSC-related transgenes, gata2a:GFP and runx1:mCherry. The double-positive fraction of gata2a:GFP and runx1:mCherry (gata2a+ runx1+) was detected at approximately 0.16% in the kidney, the main hematopoietic organ in teleosts. Transcriptome analysis revealed that gata2a+ runx1+ cells showed typical molecular signatures of HSCs, including upregulation of gata2b, gfi1aa, runx1t1, pbx1b, and meis1b. Transplantation assays demonstrated that long-term repopulating HSCs were highly enriched within the gata2a+ runx1+ fraction. In contrast, colony-forming assays showed that gata2a- runx1+ cells abundantly contain erythroid- and/or myeloid-primed progenitors. Thus, our purification method of HSCs in the zebrafish kidney is useful to identify molecular cues needed to regulate self-renewal and differentiation of HSCs.