Abstract
BackgroundIn insects, continuous growth requires the periodic replacement of the exoskeleton. Once the remains of the exoskeleton from the previous stage have been shed during ecdysis, the new one is rapidly sclerotized (hardened) and melanized (pigmented), a process collectively known as tanning. The rapid tanning that occurs after ecdysis is critical for insect survival, as it reduces desiccation, and gives the exoskeleton the rigidity needed to support the internal organs and to provide a solid anchor for the muscles. This rapid postecdysial tanning is triggered by the “tanning hormone”, bursicon. Since bursicon is released into the hemolymph, it has naturally been assumed that it would act on the epidermal cells to cause the tanning of the overlying exoskeleton.ResultsHere we investigated the site of bursicon action in Drosophila by examining the consequences on tanning of disabling the bursicon receptor (encoded by the rickets gene) in different tissues. To our surprise, we found that rapid tanning does not require rickets function in the epidermis but requires it instead in peptidergic neurons of the ventral nervous system (VNS). Although we were unable to identify the signal that is transmitted from the VNS to the epidermis, we show that neurons that express the Drosophila insulin-like peptide ILP7, but not the ILP7 peptide itself, are involved. In addition, we found that some of the bursicon targets involved in melanization are different from those that cause sclerotization.ConclusionsOur findings show that bursicon does not act directly on the epidermis to cause the tanning of the overlying exoskeleton but instead requires an intermediary messenger produced by peptidergic neurons within the central nervous system. Thus, this work has uncovered an unexpected layer of control in a process that is critical for insect survival, which will significantly alter the direction of future research aimed at understanding how rapid postecdysial tanning occurs.
Highlights
In insects, continuous growth requires the periodic replacement of the exoskeleton
The rapid tanning of the cuticle that occurs after ecdysis is under the control of the so-called “tanning hormone”, bursicon, which is highly conserved among insects [4,5,6]
We found that RK is required in a small set of peptidergic neurons in the ventral nervous system (VNS) in order for the rapid melanization and sclerotization of the cuticle to occur following adult emergence
Summary
Continuous growth requires the periodic replacement of the exoskeleton. Once the remains of the exoskeleton from the previous stage have been shed during ecdysis, the new one is rapidly sclerotized (hardened) and melanized (pigmented), a process collectively known as tanning. The rapid tanning that occurs after ecdysis is critical for insect survival, as it reduces desiccation, and gives the exoskeleton the rigidity needed to support the internal organs and to provide a solid anchor for the muscles. It has been assumed that it would act directly on the epidermis to cause the secretion of melanin and reactive quinones into the overlying extracellular cuticular matrix [13,14,15] Consistent with this hypothesis, rk is expressed in epidermal cells, and rk mutants show a delay in the phosphorylation of epithelial TH, which is necessary for the activation of the tanning pathway [13]
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have