prothoracicotropic hormone Usage And Synthesis

Description

PTTH was one of the earliest hormones discovered in insects. PTTH regulates insect molting and metamorphosis by promoting the biosynthesis and release of the molting hormone ecdysone from the prothoracic glands.

Structure

The mature PTTH forms a homodimer linked by an interchain disulfide bond while a cystine knot motif composed of three intrachain disulfide bridges is likely formed within each chain.Silkworm PTTH has been reported to have a carbohydrate chain at Asn,although its recombinant protein lacking the sugar chain also exhibits activity to induce adult development.Although the seven Cys residues that form inter- and intrachain disulfide bonds are highly conserved among PTTHs of various insect species, their primary structures are much less conserved.

Biological functions

The primary function of PTTH is to promote the biosynthesis of the molting hormone ecdysone in the prothoracic glands in response to environmental stimuli. This is best demonstrated by its regulatory role in pupal diapause; for example, in the cabbage army moth Mamestra brassicae, the hemolymph PTTH titer is reduced during the diapause period, but it is released into the hemolymph to promote ecdysone biosynthesis when the environmental condition allows for adult development.

Regulation of synthesis and release

The silkworm PTTHproduced in the brain neurosecretory cells is transported through their axons and stored in the corpora allata. In response to environmental stimuli such as the light-dark cycle, PTTH is released from the corpora allata into the hemolymph and the transient increase of its concentration in the hemolymph stimulates ecdysone biosynthesis in the prothoracic glands.In contrast, Drosophila PTTH is secreted in proximity of the prothoracic gland cells within the ring gland from axon terminals that directly contact the gland.Upstream neurons that innervate the PTTH-producing neurons and regulate their activity are beginning to be identified in D. melanogaster.