CER1 (cerberus 1) is a secreted antagonist of bone morphogenetic protein (BMP) and Nodal signaling pathways that plays critical roles in embryonic development and bone homeostasis. During early embryogenesis, CER1 inhibits BMP and Nodal signaling through receptor interactions with ACVR1B/ACVR1C and BMPR family members, respectively, to promote anterior neural induction and suppress non-neural differentiation 1. In human embryonic stem cells, CER1 expression is regulated by WNT and Nodal signaling pathways and marks commitment to endodermal lineages 12. LHX2 transcription factor promotes neural differentiation partly by upregulating CER1 to antagonize BMP and WNT signaling 3. Clinically, CER1 genetic variants are strongly associated with osteoporosis pathogenesis in postmenopausal women. Multiple CER1 polymorphisms correlate with reduced bone mineral density, elevated parathyroid hormone and calcitonin levels, and increased fracture risk 45. Notably, the c.507+506G>T polymorphism independently associates with hip and vertebral fractures, suggesting CER1 variations may serve as predictive markers for osteoporotic fracture risk 5. CER1 appears functionally conserved in primates for regulating early embryogenesis but shows evolutionary divergence from rodent orthologs 1.