Noggin, also called SYM1, is a secreted glycoprotein and belongs to a group of diffusible proteins which bind to ligands of the TGF-β family. Noggin has a complex pattern of expression during embryogenesis and is expressed in the central nervous system, as well as in several peripheral tissues such as lung, skeletal muscle and skin in adult (1-2). It was originally identified as a BMP-4 antagonist whose action is critical for proper formation of the head and other dorsal structures. Consequently, Noggin has been shown to modulate the activities of other BMPs, as well as, chordin and follistatin (3). Noggin plays a crucial role in bone development, joint formation, and neural tube fusion and can be used as a tool to differentiate human embryonic stem cells into neural precursor cells. Targeted deletion of Noggin in mice results in prenatal death and recessive phenotype displaying a severely malformed skeletal system (4). Conversely, transgenic mice over-expressing Noggin in mature osteoblasts display impaired osteoblastic differentiation, reduced bone formation, and severe osteoporosis.

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