Hematopoietic heterogeneity starts at the hemogenic endothelium.

Hematopoietic stem cells are heterogenous during develop-ment and adulthood;however,when and how this hetero-geneity begins is still not well understood.In a new study published in Cell Research,Xia et al.show that hemogenic endothelial cells are heterogeneous and the transcription factor SPI1 in mammals or Spi2 in zebrafish is partially responsible for the establishment of this heterogeneity.