The alimentary canal of the Drosophila larva is essential for survival of the organism. The gut tube is an intricate network of tissues interacting with the parasympathetic nervous system. The midgut, the region of the Drosophila gut that has the largest variety of cell types, plays a vital role in digestion and has been minimally studied. We have discovered a novel region in the larval midgut that we believe to be a portion of the Drosophila autonomic nervous system, we call this region the SCANS, or Superior Cuprophilic Autonomic Nervous System. This region has three distinct features: (1) 7-9 novel enteroendocrine cells, (2) a valve-like portion, and (3) muscular attachments to the dorsal gastric caeca. The novel enteroendocrine cells have a unique bottle-shaped structure with an apical lamellipodial head that projects into the lumen, from which they get their name the lettuce head cells (LHC), and a large body that is embedded within the endothelial lining of the midgut. The posterior projection and attachment of the dorsal gastric caeca to the SCANS region have allowed us to rearrange the anatomical design of the Drosophila larval midgut from the previous dogma wherein all four caeca extend anteriorly. The discovery of the SCANS region of the midgut, and the LHC, has led us to believe that there is peristaltic regulation occurring much like regulatory cells of the human digestive system. Given the location of the LHC in the gut tube, the expression of nervous system markers such as elav, Ddc and Cha in LHC, and the association of LHC with longitudinal visceral muscles, I will present in this study that the LHC are required for the regulation of muscle contractions in the larval midgut. I have effectively screened 37 Gal 4 enhancer traps and recorded which ones are expressed both in the midgut and specifically in the LHC alone. One of which, DJ752, expresses solely in the LHC during third instar of larval development, and was chosen as the experimental line for many of the assays. I have effectively cloned and characterized the DJ752 Gal 4 insert, which is located within the Enhancer of Split [E(spl)] region on chromosome 3, and with this information have concluded that the LHC are indeed enteroendocrine cells. Ablation of the LHC using cytotoxins with the Gal 4/Gal 80 ts system resulted in total loss of peristaltic movement within the larval midgut. Neither the morphology nor the digestive ability of the larvae were compromised when the LHC were ablated. Ectopic activation of the LHC using the Channelrhodopsin-2 transgene resulted in a significant increase in gut contractions showing that the anterior midgut functions as an independent unit from the remainder of the Drosophila alimentary canal.
|Commitee:||Hens, Mark, Katula, Karen|
|School:||The University of North Carolina at Greensboro|
|Department:||College of Arts & Sciences: Biology|
|School Location:||United States -- North Carolina|
|Source:||MAI 47/01M, Masters Abstracts International|
|Subjects:||Biology, Genetics, Cellular biology|
|Keywords:||Caeca, Digestion, Drosophila, LHC, Larval, Midgut, SCANS|
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