Year of Publication
Doctor of Philosophy (PhD)
Agriculture, Food and Environment
Dr. Subba Reddy Palli
Remodeling of larval tissues including the midgut is essential for the completion of metamorphosis in the yellow fever mosquito, Aedes aegypti (Diptera: Culicidae). The midgut structure and function have been extensively studied in adult Ae. aegypti, because adult females need to blood feed to reproduce, and the alimentary canal is the first barrier that encounters pathogens ingested through the blood meal. The midgut of Ae. aegypti undergoes remodeling during the larval-pupal metamorphosis. The degeneration of larval cells and the proliferation and differentiation of stem cells to form pupal-adult midgut are the major events that take place during metamorphosis. Juvenile hormones (JH) and ecdysteroids (20-hydroxyecdysone, 20E, is the most active form) are known to regulate midgut remodeling. Ae. aegypti is a disease-carrying mosquito that can spread dengue fever, Zika fever, chikungunya, and yellow fever viruses. Therefore, research is needed to understand the mechanisms of midgut remodeling to help develop strategies for population suppression and preventing pathogen transmissions.
This dissertation investigated how JH regulates midgut remodeling during metamorphosis. Morphological observations and analysis of RNA-sequence data showed that the application of JH analog methoprene suppresses ecdysteroid induction of autophagy (programmed cell death) of larval midgut cells during metamorphosis of Ae. aegypti. RNA interference (RNAi) was used to study the function of autophagy-related genes AMBRA1 and ATG8 in midgut remodeling. The knockdown of AMBRA1 and ATG8 prevented midgut remodeling and caused mortality during the pupal stage. The real-time quantitative PCR (RT-qPCR) analysis showed that methoprene suppressed the expression of autophagy-related genes and blocked degradation of larval midgut cells. This research also investigated how JH III and 20E regulate miRNA biogenesis in Ae. aegypti. A small RNA-Seq (sRNA) approach was used to identify and characterize miRNAs regulated by JH III and 20E in Ae. aegypti Aag-2 cells. Forty-four JH and 20E-regulated miRNAs were identified. Among them, mir-115, 117, and 118 were shown to be involved in insect metamorphosis and molting. JH and 20E control miRNA expression by regulating their host gene transcription through their receptors, methoprene tolerance (Met) and the ecdysone receptor (EcR), respectively.
These studies have provided insights into the importance of JH in the regulation of midgut remodeling in Ae. aegypti, and evidence for possible mechanisms of JH modulation of ATG genes. Also, JH and 20E working through their receptors Met and EcR influence miRNA biogenesis by controlling the expression of their host genes. Overall, the data from this research will help to develop effective strategies for vector population suppression and disease transmission leading to the prevention of mosquito-borne diseases.
Digital Object Identifier (DOI)
Albishi, Najla Mohammed, "Midgut metamorphosis in the yellow fever mosquito, Aedes aegypti" (2022). Theses and Dissertations--Entomology. 65.
Available for download on Friday, August 02, 2024