The role of the NO pathway and its upstream and downstream regulation of larval settlement of a major marine soft-fouler bugula neritina

Abstract

Marine invertebrates are of great importance to both ecosystems and economics. Most of marine invertebrates have a biphasic life cycle, during which they start as planktonic larvae and become sessile after they settle on a suitable substratum. The interesting life history of marine invertebrates has drawn a lot of attention from researchers. However, the molecular mechanisms underlying the process of larval settlement and metamorphosis remain largely unclear. In the present thesis, I mainly focused on understanding the roles of NO pathway, which was intensively studied previously in larval settlement, and its related upstream and downstream regulators in settlement and metamorphosis of B. neritina. Firstly, I investigated the role of arginine kinase (AK), which share the same substrate with NO synthase. AK was reported to be involved in the larval settlement of the barnacle Amphibalanus amphitrite. In the present study, I found that the inhibition of AK activity could reduce larval settlement rate in B. neritina. In addition, AK was highly expressed in the swimming larva stage, and mainly localized to muscle tissues. Based on these results, I concluded that AK exerted effect on larval settlement possibly through influencing muscle energy supply. Secondly, I studied the upstream regulator of NO pathway. In mammalian cells, HSP90 was reported to activate NO synthase. In order to determine if the same interaction between NO synthase and HSP90 exists in B. neritina in terms of regulating larval settlement, I performed a series of experiments. I discovered that HSP90 inhibitor was able to attenuate the inhibitory effect of NO donor on B. neritina larval settlement. Moreover, the signal of NO diminished in larvae upon incubation of HSP90 inhibitor. The protein expression level of NO synthase in swimming larvae significantly dropped in response to HSP90 treatment. All these results suggest that HSP90 interacts with NO pathway through mediating NO synthase. In summary, this thesis work provided insights into the molecular mechanism underlying larval settlement of B. neritina and uncovered the essential roles of two regulators of NO pathway during the larvae settlement process in B. neritina, a mechanism that might exist among different phyla in marine invertebrates.

Date of Award	2017
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology