Information AboutSonic Hedgehog |
| CATEGORIES ABOUT SONIC HEDGEHOG | |
| proteins | |
| morphogens | |
| hint domain | |
Sonic hedgehog homolog (SHH) is one of five Protein s in the Vertebrate hedgehog (HH) family thus far described, the others being desert hedgehog (DHH), indian hedgehog (IHH), echidna hedgehog (EHH) and tiggywinkle hedgehog (TwHH). The hedgehog gene (''hh'') was first identifed in the classic Heidelberg screens of Eric Wieschaus and Christiane Nusslein-Volhard , as published in 1978. These Screens , which led to their both winning the Nobel Prize in 1995, identified genes that control the segmentation pattern of '' Drosophila Melanogaster '' (fruit fly) embryos. The ''hh'' loss of function Mutant Phenotype causes the Embryo s to be covered with denticles (small pointy projections), much like a Hedgehog . Investigations aimed at finding a ''hedgehog'' equivalent in mammals, revealed three , and ''tiggywinkle hedgehog'' named for a character from Beatrix Potter's books for children. Of the ''hh'' homologues, ''shh'' has been found to have the most critical roles in development, acting as a Morphogen involved in patterning many systems, including the limb and midline structures in the Brain and Spinal Cord . Mutations in the human sonic hedgehog Gene , ''SHH'', cause Holoprosencephaly type 3 (HPE3) as a result of the loss of the ventral midline. Sonic hedgehog is secreted by the zone of polarizing activity (ZPA), which is located on posterior side of a limb bud in an embryo. The sonic hedgehog transcription pathway has also been linked to the formation of specific kinds of cancerous tumours. More recently, sonic hedgehog has also been shown to act as an Axonal Guidance Cue . Specifically, it attracts Retinal Ganglion Cell (RGC) axons at low concentrations and repels them at higher concentrations. Hedgehog inducers bind to proteins of the Patched family, which are transmembrane proteins in the Cell Membrane s of cells responsive to hedgehog. In the absence of hedghog Patched is bound to Smoothened , another membrane protein. This setup keeps the Cubitus Interruptus (Ci) protein bound to Microtubule s in the Cytoplasm of the cell, which leads to the cleaving of the protein. Part of the cleaved molecule then enters the Nucleus and acts as a Repressor to certain genes. When hedgehog binds to Patched, Smoothened allows Ci to dissociate from the microtubules, and hence remain as an intact protein. This protein also enters the nucleus, but in this state acts to activate the genes it once repressed. Some clinicians and scientists criticise giving genes frivolous or quirky names, calling it inappropriate that patients with "a serious illness or Disability are told that they or their child have a Mutation in a gene such as ''Sonic hedgehog''." SEE ALSO EXTERNAL LINKS REFERENCES |
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