Browsing by Subject "Nematoda"
Now showing 1 - 2 of 2
- Results Per Page
- Sort Options
Item DAF-12: A Novel Drug Target in Parasitic Nematodes(2014-07-24) Schaffer, Nathaniel Elliot; Phillips, Margaret A.; Mangelsdorf, David J.; Kliewer, Steven A.; Brown, Michael S.; Ranganathan, RamaThe nuclear receptor DAF-12, first identified in C. elegans, controls nematode species' entry into and exit from metabolically hypoactive resting states. In all of the parasitic species studied thus far, that resting state is the infectious third larval (iL3) stage, and activation of the receptor in iL3 worms outside of the host induces a premature and lethal molt (Wang et al. 2009; Motola et al. 2006). In contrast, the relatively uncontrolled soybean parasite Heterodera glycines, which causes USD 1 billion of crop damage annually in the U.S. (Wrather and Koenning 2006; Davis and Tylka 2005), does not go through an iL3 stage but rather arrests as the preinfectious second juvenile (piJ2) within the egg (Davis and Tylka 2005). However, just as iL3 worms only molt to L4 when they are inside their host (Wang et al. 2009), H. glycines nematodes only hatch as infectious J2s when they are near the plant roots required to support their development (Davis and Tylka 2005). This work demonstrates the importance of the DAF-12 ortholog in H. glycines for regulating hatching and introduces the the first well-defined molecular target for controlling the spread of this important pathogen. Additionally, an ortholog with significant sequence and likely functional similarity is identified in the related parasite Globodera pallida, which causes an identical disease in other major agricultural crops including potato and tomato plants and exhibits the same arrest phenotype inside the egg as H. glycines. Finally, a DAF-12 ortholog is cloned from Onchocerca gutturosa, one of several species in the Onchocerca genus that causes the disease onchocerciasis in both humans and livestock. Importantly, since onchocerciasis continues to elude the eradication efforts of several well-funded international programs, both an existing agonist and an avenue to identify endogenous agonists for the receptor are identified. These studies offer direction for the development of novel therapeutics to control these socially and economically important pathogens.Item Genetic Analysis of Grinder Formation in Caenorhabditis Elegans: Regulation by RAB-6.2 and Its GTPase Activating Protein EAT-17(2004-12-15) Anselmo, Sarah Straud; Avery, LeonThe C. elegans grinder is an intricately designed, macromolecular structure located in the terminal bulb of the pharynx. It acts as the teeth of C. elegans, crushing bacteria before they are passed to the intestine. The grinder is a specialized cuticular structure and is shed and rebuilt at each larval molt. While we have a fairly decent view regarding the mechanics of the grinder, we know surprisingly little about its composition or how it is formed. The nematode grinder has been studied for over 100 years, but no one has yet described the molecular events controlling grinder formation and/or grinder function. To understand how the grinder is formed, I have focused on cloning and characterizing eat-17. eat-17 mutants have rudimentary, malformed grinders: the grinder plates are smaller than normal, disorganized in structure, and often improperly arranged. I found that eat-17 encodes an ~825 amino acid Rab GTPase activating protein with a series of C-terminal coiled-coil domains. Its closest human homolog is Evi5, a putative oncogene whose function is not currently understood. Rabs are key regulators of vesicle transport, and cycle between active, GTP bound and inactive, GDP bound states. GTPase activating proteins (GAPs) catalyze the hydrolysis of GTP, allowing Rabs to be extracted from membranes and recycled for additional rounds of signaling. I found that the GAP activity of EAT-17 is important for its function: 21% (16/76) of mutants expressing a wild-type version of eat-17 are rescued for defects in grinder formation, while only 2.9% (3/113) of worms expressing catalytically inactive versions of EAT-17 are rescued. I performed RNAi against the 27 putative Rabs in the C. elegans genome and found that rab-6.2 RNAi causes grinder defects similar to those seen in eat-17 mutants. GFP reporters show that both EAT-17 and RAB-6.2 are expressed in terminal bulb muscle, the site of grinder secretion. By yeast two-hybrid, I have demonstrated a direct interaction between RAB-6.2 and EAT-17. These data suggest that EAT-17 and RAB-6.2 work together in regulating grinder formation. Genetic interaction studies suggest that RAB-6.1 may play a role in a similar cellular process.