Abstract
BackgroundThe underlying cellular and molecular mechanisms that coordinate the physiological processes in digestion are complex, cryptic, and involve the integration of multiple cellular and organ systems. In all intestines, peristaltic action of the gut moves food through the various stages of digestion from the anterior end towards the posterior, with the rate of flow dependent on signals, both intrinsic and extrinsic to the gut itself.ResultsWe have identified an enteroendocrine cell type that regulates gut motility in the Drosophila melanogaster larval midgut. These cells are located at the junction of the anterior and the acidic portions of the midgut and are a group of enteroendocrine cells that express the peptide hormone Diuretic Hormone 31 in this region of the gut. Using cell ablation and ectopic activation via expression of the Chlamydomonas reinhardtii blue light-activated channelopsin, we demonstrate that these enteroendocrine cells are both necessary and sufficient for the peristalsis in the junction region of the midgut and require the Diuretic Hormone 31 to affect normal peristalsis in this region. Within the same junction region of the midgut, we have also identified morphological features suggesting that this region acts as a valve that regulates the transit of food from the anterior midgut into the acidic portion of the gut.ConclusionsWe have characterized and described a set of enteroendocrine cells called the Midgut Junction DH31 expressing cells that are required for peristaltic movement in the junction region between the anterior portion and acidic region of the larval midgut of Drosophila melanogaster. We have shown that the Midgut Junction DH31 expressing cells are necessary and sufficient for motility and that the peptide hormone DH31 is required for peristalsis in the junction region of the midgut. The Drosophila model system will allow for a further dissection of the digestion process and provide a better understanding of the mechanisms that regulate digestion in all organisms.
Highlights
The underlying cellular and molecular mechanisms that coordinate the physiological processes in digestion are complex, cryptic, and involve the integration of multiple cellular and organ systems
Screen of midgut expressing Gal4 enhancer trap lines To better understand the different cell types within the larval midgut, we performed a screen of previously identified Gal4 enhancer trap lines and transgenic Gal4 constructs, reported to express in the gut, but which have not been characterized in detail [45,46,47]
Midgut Junction Diuretic Hormone 31 (DH31) expressing cells express acetylcholine receptors (AChR) and AllostatinB/MIP cells express CHAT In addition to DH31, we found that the Midgut Junction DH31 expressing cells express two Gal4 reporters for the genes involved in neurotransmitter biosynthesis, Choline acetyltransferase (Cha) and Dopa decarboxylase (Ddc) [53,54,55]
Summary
The underlying cellular and molecular mechanisms that coordinate the physiological processes in digestion are complex, cryptic, and involve the integration of multiple cellular and organ systems. Digestive systems are adapted to diverse feeding behaviours, they share an overall similarity in their organization, and all coordinate nervous system and endocrine input to govern the movement and the processing of food within the alimentary canal [4,5,6,7,8,9]. Central to these concepts is the digestion of food within the gut. Many of these neuropeptide hormones are expressed in the central nervous system where they have been shown to influence behaviour and circadian rhythm [4,9,31], the significance of neuropeptide hormone secretion by gut enteroendocrine cells remains unclear
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