Sonic Hedgehog - Function

Function

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, spinal cord, the thalamus by the zona limitans intrathalamica and the teeth. 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 at 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. It has been demonstrated that Shh attracts commissural axons at the ventral midline of the developing spinal cord. Specifically, Shh attracts retinal ganglion cell (RGC) axons at low concentrations and repels them at higher concentrations. The absence (non-expression) of Shh has been shown to control the growth of nascent hind limbs in cetaceans (whales and dolphins).

Read more about this topic:  Sonic Hedgehog

Famous quotes containing the word function:

    As a medium of exchange,... worrying regulates intimacy, and it is often an appropriate response to ordinary demands that begin to feel excessive. But from a modernized Freudian view, worrying—as a reflex response to demand—never puts the self or the objects of its interest into question, and that is precisely its function in psychic life. It domesticates self-doubt.
    Adam Phillips, British child psychoanalyst. “Worrying and Its Discontents,” in On Kissing, Tickling, and Being Bored, p. 58, Harvard University Press (1993)

    Our father has an even more important function than modeling manhood for us. He is also the authority to let us relax the requirements of the masculine model: if our father accepts us, then that declares us masculine enough to join the company of men. We, in effect, have our diploma in masculinity and can go on to develop other skills.
    Frank Pittman (20th century)

    Literature does not exist in a vacuum. Writers as such have a definite social function exactly proportional to their ability as writers. This is their main use.
    Ezra Pound (1885–1972)