Academic literature on the topic 'Jhamak'

Doctor of Philosophy<br>Entomology<br>David C. Margolies<br>Yoonseong Park<br>Insect metamorphosis is driven by two major hormones, juvenile hormone (JH) and ecdysone (Ec). The presence of JH with an Ec peak in each stadium results in larval-larval molting whereas in the last larval instar a decline of JH to undetectable level combined with pulses of Ec leads to larval-pupal metamorphosis. Larval-pupal metamorphosis normally occurs after a certain number of larval instar and upon reaching a certain size (critical weight). However, in the flour beetle, Tribolium freemani, under crowded conditions larva continue larval-larval molting (LLC) without pupation for longer than 14 instars (6 months). Previous studies have implicated high JH titer as preventing the metamorphosis leading to supernumerary molts. My investigation of JH roles in LLC started by asking whether suppression of JH would rescue the LLC phenotype and allow pupal metamorphosis. Using RNA interference (RNAi), I found that under crowded conditions RNAi of T. freemani methyltransferase3 (TfMT3), which encodes a crucial enzyme for the final methylation step in the JH biosynthesis, or RNAi of T. freemani Krüppel homolog1 (TfKr-h1), the JH downstream gene, did not rescue the larvae but resulted in prepupal lethality. Surprisingly, under crowded conditions prepupal lethality was rescued by RNAi of both TfMT3 and TfKr-h1 administered together, although developmental arrest occurred at the pharate adult stage; this is also the phenotype of TfKr-h1 RNAi-treated larvae under isolated conditions. In investigations of the role of Ec titer in LLC, lethality of the larvae with RNAi of TfMT3 under crowded conditions was associated with the loss of the major ecdysteroid peak, while TfKr-h1 RNAi-treated larvae under crowded conditions showed a delayed, but normal, Ec peak occurring at prepupal arrest. The pattern of Ec peak in RNAi of both TfMT3 and TfKr-h1 together was similar to that with TfKr-h1 RNAi alone. I suggest that a hormonal imbalance, high JH and high Ec in the prepupal arrest of TfKr-h1 RNAi, was rescued by RNAi of both TfMT3 and TfKr-h1 for low JH and high Ec. These results demonstrate that the signaling pathways for LLC are through at least two independent pathways; JH biosynthesis and TfKr-h1-mediated JH response.

Juvenile hormones (JHs) are key regulators of both metamorphosis and adult reproductive processes. The role of two key enzymes in the biosynthetic pathway of JH were examined: Farnesoic Acid O-Methyltransferase (FAMeT) and Juvenile Hormone Acid Methyltransferase (JHAMT). In crustaceans, FAMeT has been found to methylate farnesoic acid (FA), producing methyl farnesoate (MF) prior to epoxidation at the penultimate stage of JH biosynthesis. JHAMT was discovered more recently in the silkworm Bombyx mori and converts epoxidated FA (JHacids) to active JH through methylation using S-adenosyl-L-methionine (SAM). The aim of the proposed research is to examine the influence of a) decreasing the amount of FAMeT produced using an enhancer trapping P-element and b) increasing the levels of JHAMT and FAMeT in specific tissues using GAL4 overexpression techniques. Immunohistochemical analysis was used to confirm the presence of FAMeT in the CA of D. melanogaster ring glands. Analysis of MF, JHIII and JHB3 release in wild type and mutant stocks in the presence and absence of Drome AST (PISCF-type) suggest that Drosophila FAMeT has little if any effect on the sesquiterpenoid biosynthesis. Drome-AST appears to have a select effect on JHB3 biosynthesis and not MF or JHIII. Analysis of JHB3 release from larval and adult flies ubiquitously overexpressing JHAMT showed a significant increase when compared to wildtype (p<0.01 and p<0.0001 respectively). No significant difference was seen in JHB3 release in flies ubiquitously overexpressing FAMeT. A significant increase in hatching success was seen in flies overexpressing FAMeT in the larval ring gland and oocytes (p<0.05) whereas no significant decrease was seen in JHAMT-overexpressing flies during development. A significant extension of lifespan was also seen when FAMeT was overexpressed in the border and follicle cells of the oocyte (p<0.0001). The direct role of JHAMT in JHB3 synthesis has been demonstrated. The involvement of FAMeT and JHAMT in development and longevity may require other interacting proteins to elicit an effect, which is a limiting factor in overexpression experiments of the two enzymes. Additionally, this is the first example of AST action within D. melanogaster.<br>Thesis (Master, Biology) -- Queen's University, 2007-09-27 20:08:23.69