Noggin is also known as NOG£¬SYM1, SYNS1 and is a secreted homodimeric glycoprotein whose scaffold contains a cystine-knot topology similar to that of BMPs.Secreted Noggin probably remains close to the cell surface due to its binding of heparincontaining proteoglycans.Noggin inhibits TGF-¦Â signal transduction by binding to TGF-¦Â family ligands and preventing them from binding to their corresponding receptors. Noggin plays a key role in neural induction by inhibiting BMP4, along with other TGF-¦Â signaling inhibitors such as chordin and follistatin. Mouse knockout experiments have demonstrated that noggin also plays a crucial role in bone development, joint formation, and neural tube fusion. During embryogenesis, Noggin antagonizes specific BMPs at defined times, for example, during neural tube, somite and cardiomyocyte growth and patterning. During skeletal development, Noggin prevents chondrocyte hyperplasia, thus allowing proper formation of joints. During culture of human embryonic stem cells (hESC) or neural stem cells under certain conditions, addition of Noggin to antagonize BMP activity may allow stem cells to proliferate while maintaining their undifferentiated state, or alternatively, to differentiate into dopaminergic neurons Noggin also appears to maintain adult stem cell populations in vivo, for example, maintaining neural stem cells within the hippocampus.