Transcription factor Maf promotes expression of repressor Zeb2 to drive microglia development in primitive hematopoiesis.

Microglia arise exclusively from yolk sac progenitors during primitive hematopoiesis, while other tissue-resident macrophages originate during transient-definitive and definitive hematopoiesis. Macrophage development requires the transcriptional repressor zinc finger E-box-binding homeobox 2 (Zeb2), and those derived from definitive hematopoiesis depend on the -165 kb Zeb2 enhancer. However, microglia develop normally in Zeb2(Δ-165kb) mice, indicating that primitive hematopoiesis relies on a distinct genetic program. We identified the molecular basis underlying this difference and show that all macrophages in Zeb2(Δ-165kb) mice arise exclusively during primitive hematopoiesis. The transcription factors musculoaponeurotic fibrosarcoma oncogene homolog (Maf) and Jun were expressed by primitive hematopoietic progenitors but absent in progenitors of subsequent hematopoietic waves. Together, Maf and Jun induced Zeb2 expression independently of the -165 kb Zeb2 enhancer and restored macrophage development from adult bone marrow progenitors in Zeb2(Δ-165kb) mice. Finally, Maf-deficient embryos exhibited severe ablation of primitive microglia development. These results define distinct transcriptional pathways controlling macrophage development during primitive hematopoiesis.