Accelerates cholesterol efflux from endothelial cells to high-density lipoprotein (HDL) and thereby regulates angiogenesis (PubMed:23719382). Orchestrates hematopoietic stem and progenitor cell emergence from the hemogenic endothelium, a type of specialized endothelium manifesting hematopoietic potential. YJEFN3-mediated cholesterol efflux activates endothelial SREBF2, the master transcription factor for cholesterol biosynthesis, which in turn transactivates NOTCH and promotes hematopoietic stem and progenitor cell emergence (PubMed:30705153). Interacts with APOA1 (PubMed:23719382). Binds to HDL (PubMed:23719382). Expression in 24-36 hours post-fertilization (hpf) embryos shows a clear segmental pattern. By 48 hpf, when segmental angiogenesis is completed, is no longer expressed in somites. Mutants appear morphologically normal and have no observable effect on dorsal aorta specification (PubMed:30705153). Mutants have reduced the number of nascent hematopoietic stem cells in the ventral dorsal aorta between 28 and 60 hours post-fertilization (hpf) (PubMed:30705153). Mutant embryos show increased cholesterol content (PubMed:30705153, PubMed:23719382).