Myelin-associated glycoprotein (MAG, Siglec-4) is a type 1 transmembrane proteinglycoprotein localized in periaxonal Schwann cell and oligodendrocyte membranes, where it plays a role in glial-axonal interactions. MAG is a member of the SIGLEC family of proteins and is a functional ligand of the NOGO-66 receptor, NgR.[5] MAG is believed to be involved in myelination during nerve regeneration in the PNS[6] and is vital for the long-term survival of the myelinated axons following myelinogenesis.[7] In the CNS MAG is one of three main myelin-associated inhibitors of axonal regeneration after injury,[8] making it an important protein for future research on neurogenesis in the CNS.
MAG is a 100 kDA glycoprotein.[9] Uncleaved MAG is a complete transmembrane form, which acts as a signaling and adhesion molecule.[10] MAG can also act as a signaling molecule as a soluble protein after it has been proteolytically shed. This form of the protein is called dMAG.[11]
MAG has an extended conformation of five immunoglobulin (Ig) domains and a homodimeric arrangement involving membrane-proximal domains Ig4 and Ig5. MAG-oligosaccharide complex structures and biophysical assays show how MAG engages axonal gangliosides at domain Ig1.[12]
MAG is a critical protein in the formation and maintenance of myelin sheaths. MAG is localized on the inner membrane of the myelin sheath and interacts with axonal membrane proteins to attach the myelin sheath to the axon.[13] Mutations to the MAG gene are implicated in demyelination diseases such as multiple sclerosis.[14]
Axons in the central nervous system do not regenerate after injury the same way that axons in the peripheral nervous system do.[15] The mechanism responsible for inhibited neuroregeneration is regulated by three main proteins, one of which is MAG.[16][17] The exact mechanism through which MAG inhibits neuroregeneration appears to be through binding of NgR. This receptor is also bound by Nogo protein, suggesting that the mechanism of myelin-associated inhibition of axon regeneration through NgR the has redundant ligands[clarification needed], furthering the inhibition.[18] MAG binds with high affinity to NgR, suggesting that it is equally as responsible for inhibition of axon regeneration as Nogo.[19]
Once MAG (or Nogo) has bound to NgR, NgR activates the rho kinase (ROCK) pathway. The activation of the rho kinase pathway leads to the phosphorylation of proteins which inhibit neurite outgrowth.[20]
^McKerracher L, David S, Jackson DL, Kottis V, Dunn RJ, Braun PE (October 1994). "Identification of myelin-associated glycoprotein as a major myelin-derived inhibitor of neurite growth". Neuron. 13 (4): 805–11. doi:10.1016/0896-6273(94)90247-x. PMID7524558. S2CID28429007.
^Lopez PH (2014). "Role of Myelin-Associated Glycoprotein (Siglec-4a) in the Nervous System". Glycobiology of the Nervous System. Advances in Neurobiology. Vol. 9. pp. 245–62. doi:10.1007/978-1-4939-1154-7_11. ISBN 978-1-4939-1153-0. PMID25151382.
^Lopez PH (2014). "Role of Myelin-Associated Glycoprotein (Siglec-4a) in the Nervous System". Glycobiology of the Nervous System. Advances in Neurobiology. Vol. 9. pp. 245–62. doi:10.1007/978-1-4939-1154-7_11. ISBN 978-1-4939-1153-0. PMID25151382.
^McKerracher L, David S, Jackson DL, Kottis V, Dunn RJ, Braun PE (October 1994). "Identification of myelin-associated glycoprotein as a major myelin-derived inhibitor of neurite growth". Neuron. 13 (4): 805–11. doi:10.1016/0896-6273(94)90247-x. PMID7524558. S2CID28429007.
^Mukhopadhyay G, Doherty P, Walsh FS, Crocker PR, Filbin MT (September 1994). "A novel role for myelin-associated glycoprotein as an inhibitor of axonal regeneration". Neuron. 13 (3): 757–67. doi:10.1016/0896-6273(94)90042-6. PMID7522484. S2CID928929.
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction
Well, that’s interesting to know that Psilotum nudum are known as whisk ferns. Psilotum nudum is the commoner species of the two. While the P. flaccidum is a rare species and is found in the tropical islands. Both the species are usually epiphytic in habit and grow upon tree ferns. These species may also be terrestrial and grow in humus or in the crevices of the rocks.
View the detailed Guide of Psilotum nudum: Detailed Study Of Psilotum Nudum (Whisk Fern), Classification, Anatomy, Reproduction