Ligand of the EGF receptor/EGFR and ERBB4. Stimulates EGFR and ERBB4 tyrosine phosphorylation (By similarity). Contributes to inflammation, wound healing, tissue repair, and oocyte maturation by regulating angiogenesis and vascular remodeling and by stimulating cell proliferation (PubMed:24631357). Interacts with EGFR and ERBB4. Expressed in 7-day-old embryos with levels then falling to very low or undetectable amounts. Not detected in adult.