Ecdysis controlling hormones

Ecdysone stimulates the synthesis of RNA in tissues. Visual demonstration of the effect is provided by its action on polytene chromosomes of fly larvae (Fig. 26-14).361 Fifteen minutes after the application of ecdysone, a puff is induced on one band of the chromosome a second puff forms at a later time while a preexisting puff diminishes. Thus, like steroid hormones in mammals, ecdysone appears to have a direct controlling effect on transcription. The cuticle-shedding process (ecdysis) is initiated by the brain peptide eclosian. However, the brain may be responding to the ecdysis-triggeiing hormone, a peptide that is secreted by a series of epitracheal glands located in various segments of the body.362... 

When new cuticle Is synthesized, It Is soft and flexible so that the hydrostatic pressures unfold and expand the new cuticle thereby Increasing its surface area and concomitantly casting off the old cuticle. After ecdysis, expansion of the new cuticle Is brought to an end by the onset of sclerotlzatlon (tanning) (2), which Involves the cross-linking of cutlcular protein with ortho-qulnone The source of the ortho-qulnone Is tyrosine, whose mobilization Is controlled by eedysterone, as well as by a peptide hormone called bursIcon. 

Although It Is unknown how azadlrachtln acts as an ecdysis Inhibitor, It apparently does not act by Inhibiting chitln synthetase (32). Possibly, ecdysis Inhibition Is caused by a disruption of the tltre of ecdysterone (40, 44) or by an Interference with the neuroendocrine system, prothoradcotroplc hormone and allatotroplc hormone, which controls the tltres of molting hormone and juvenile hormone, respectively (45). 

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