Beta-1,3-N-acetylglucosaminyltransferase radical fringe, also known as radical fringe is a

protein Proteins are large biomolecules and macromolecules that comprise one or more long chains of amino acid residue (biochemistry), residues. Proteins perform a vast array of functions within organisms, including Enzyme catalysis, catalysing metab ...

that in humans is encoded by the ''RFNG'' gene. Radical fringe is a signaling

enzyme An enzyme () is a protein that acts as a biological catalyst by accelerating chemical reactions. The molecules upon which enzymes may act are called substrate (chemistry), substrates, and the enzyme converts the substrates into different mol ...

involved in the arrangement of the embryonic limb buds. It is a member of the fringe gene family, which also includes manic fringe and

lunatic fringe Lunatic fringe, a derogatory term used to characterize members of a political or social movement as extremists with eccentric or fanatical views, may refer to: * "Lunatic Fringe" (song), a 1981 song by Red Rider * LFNG, a gene in the Notch pathw ...

. It is important for the dorsoventrally patterning of the limb and has been implicated in the formation of the

apical ectodermal ridge The apical ectodermal ridge (AER) is a structure that forms from the ectodermal cells at the distal end of each limb bud and acts as a major signaling center to ensure proper development of a limb. After the limb bud induces AER formation, the AE ...

(AER). The AER is essential for the distal patterning of the limb. Experiments executed in chicken models show Radical fringe is expressed in both the dorsal ectoderm and the AER. This provides evidence that the AER forms from cells already expressing radical fringe, though further evidence is needed to confirm. Grafting experiments have shown that formation of the AER comes from signals in the limb bud

mesoderm The mesoderm is the middle layer of the three germ layers that develops during gastrulation in the very early development of the embryo of most animals. The outer layer is the ectoderm, and the inner layer is the endoderm.Langman's Medical ...

. However, radical fringe acts as a permissive signal to create a boundary for the AER to form. The knockout experiments done in chicken models suggest Radical fringe plays an integral role in wing development. Conversely, knockout experiments in mice have shown that if Radical fringe is absent no phenotypic differences occur. Further study revealed the absence of mutation is most likely due to redundancy of Manic and Lunatic fringe, which likely take over in the absence of Radical fringe. Radical, Manic, and lunatic fringe genes make up a group of enzymes known as 3-beta-N-acetylglucosaminyltransferases. They elongate O-linked fucose residues on notch receptors, which effects neurogenesis through the notch signaling pathway. While Radical fringe may not be vital for limb formation in all species, current research suggests it plays an integral role in establishing the pattern of the developing limb when expressed.

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