Ecdysis Control Sheds Another Layer James W Truman Identification of Ecdysis Triggering Hormone from an Epitracheal Endocrine System Dusan Zitnan Vocabulary Ecdysis Shedding of entire body surface including cuticular lining of fore and hindgut and tracheal system It is controlled by hormones Eclosion hormone EH a 62 aa peptide released in brain that acts on an isolated chain of abdominal ganglia Triggers pre ecdysis and ecdysis behavior Mas ETH Manduca sexta ecdysis triggering hormone Released from peripheral secretory cells Inka cells on ventral tracheal trunks near spiracle Triggers pre ecdysis and ecdysis Inka cells Peripheral secretory cells that secrete ETH Reside on ventral tracheal trunk that leads to each ganglion Part of the endocrine system of epitracheal glands EGs Pre ecdysis and Ecdysis Behavioral Characteristics Pre ecdysis Precedes natural ecdysis between larvae stages instars Synchronized Dorsoventral contractions in abdominal thoracic segments Contractions begin at most posterior segment and gradually spreads anteriorly Behavior typically lasts 60 80 min followed by ecdysis Cuticle Loosening Ecdysis Characterized by peristaltic waves of contractions originating at most posterior segment and moves anteriorly Typically lasts 10 minutes Cuticle shedding Instar developmental stages between each molt Conclusions Mas ETH is an immediate trigger for preecdysis ETH is a downstream target of EH Inka cells release ETH during ecdysis EH latent sensitivity May act directly or indirectly to promote ETH release in periphery ETH high sensitivity early in development Immediate blood borne trigger for pre ecdysis and ecdysis through direct action on nervous system Latency between hormone injection and emergence of behavior ETH 2 10min EH 15min 3 hours depending on developmental stage Can stimulate pre ecdysis and ecdysis behavior in isolated nerve cords Suggests the tracheal system is required for EH action because of the presence of EGs and not because of the presumed role of of the tracheal system in oxygenation of the nervous system Questions and Answers 1 What are three lines of evidence that the Inka cells release their contents during ecdysis viewed structure of Epitracheal Gland EG saw that Inka cells reduced in volume and lost their white appearance after ecdysis direct marking of ETH in Inka cell before and after ecdysis using immunoreactivity ETH similar to SCPb saw that ETH was present before and absent after ecdysis In the adult stage small glandular cells are lost and only Inka cells were left Inka cells still had high immunoreactivity these Inka cells could still cause ecdysis if stimulated to release contents 2 Describe how natural ecdysis motor patterns were elicited by an isolated nervous system Natural ecdysis motor patterns were elicited in an isolated nervous system of the Manduca sexta through the application of Mas ETH a 26 amino acid polypeptide believed to be the triggering hormone Removed the CNS and placed the CNS in a bath of Mas ETH recorded from electrodes attached to three dorsal nerves in the abdominal ganglia they recorded similar burst patterns between the natural ecdysis patterns and the activity in the isolated CNS 3 Why is the tracheal system necessary for stimulating ecdysis motor patterns in response to eclosion hormone The tracheal system contains Epitracheal Glands EGs that are attached to its outer walls near each segment spiracle The Inka cells are a part of the EGs which monitors the changes in the tracheae during the molting process If the old cuticle of the trachae are not digested properly pieces of the old cuticle will be left behind after molting and obstruct the airway of the organism