Mapping of complex regulatory elements by pufferfish/zebrafish transgenesis

Vertebrate hematopoiesis is a richly complex developmental system in which many transcription factors have essential and nonredundant roles (1). Some factors act as prominent controllers of differentiation in specific cell lineages, others are needed for stem cell generation, and others are needed for both. In this system, precise levels of one transcription factor relative to another in the same cell can control the direction of cell lineage choices, proliferation vs. apoptosis, lineage-specific malignant transformation, and the timing and sites of stem cell generation (2–9).