The Fibroblast Growth Factor (FGF) family consists of nine structurally related proteins that play essential roles in mammalian development, including angiogenesis, wound healing, and tumorigenesis. These FGFs interact with four FGF receptors (FGFRs), which exist in multiple splice variants. The study investigates the specific interactions between FGF ligands and FGFRs to understand their roles in developmental and physiological processes. Researchers engineered cell lines expressing major FGFR splice variants and tested the mitogenic activity of the nine FGFs. They found that FGF 1 is the only FGF that activates all FGFR splice variants. Using FGF 1 as a reference, they compared the activity of other FGFs, revealing distinct patterns of receptor activation. The study highlights the importance of FGF receptor specificity in regulating signaling pathways. It also shows that different FGFR splice forms have varying affinities for FGFs, with some forms having higher affinity for specific FGFs. The findings provide a biochemical foundation for understanding FGF signaling in development, physiology, and disease. The study also discusses the implications of alternative splicing in FGFRs and how it may influence tumor progression. The results demonstrate that FGF 1 is a universal ligand for FGFRs and may define a core binding domain. The study emphasizes the need to understand ligand-receptor interactions to identify key pairs involved in various biological processes. The research provides insights into the complex interactions between FGFs and their receptors, which are crucial for understanding their roles in health and disease.The Fibroblast Growth Factor (FGF) family consists of nine structurally related proteins that play essential roles in mammalian development, including angiogenesis, wound healing, and tumorigenesis. These FGFs interact with four FGF receptors (FGFRs), which exist in multiple splice variants. The study investigates the specific interactions between FGF ligands and FGFRs to understand their roles in developmental and physiological processes. Researchers engineered cell lines expressing major FGFR splice variants and tested the mitogenic activity of the nine FGFs. They found that FGF 1 is the only FGF that activates all FGFR splice variants. Using FGF 1 as a reference, they compared the activity of other FGFs, revealing distinct patterns of receptor activation. The study highlights the importance of FGF receptor specificity in regulating signaling pathways. It also shows that different FGFR splice forms have varying affinities for FGFs, with some forms having higher affinity for specific FGFs. The findings provide a biochemical foundation for understanding FGF signaling in development, physiology, and disease. The study also discusses the implications of alternative splicing in FGFRs and how it may influence tumor progression. The results demonstrate that FGF 1 is a universal ligand for FGFRs and may define a core binding domain. The study emphasizes the need to understand ligand-receptor interactions to identify key pairs involved in various biological processes. The research provides insights into the complex interactions between FGFs and their receptors, which are crucial for understanding their roles in health and disease.