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Title: Studies of wound inflammatory calcium signalling and mechanical forces during wound healing in drosophila
Author: Razzell, William
Awarding Body: University of Bristol
Current Institution: University of Bristol
Date of Award: 2013
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Our bodies are protected from the dangers of the external environment by barriers consisting of epithelial tissues . As such, epithelia are subject to damage which then exposes the body to pathogens and debris. To various degrees epithelial wounding occurs almost daily but without noticeable catastrophe. This is thanks to a specialised army of defense mechanisms including mobile innate immune cells that are rapidly recruited to sites of epithelial damage through alarm signals. Hydrogen peroxide has been recently identified as the earliest damage signal for recruiting innate immune cells to wound sites. The NADPH oxidase, DUOX is known to be responsible for generating the hydrogen peroxide wound attractant cue; but how DUOX is activated at the wound edge was not known. Here, I show that laser wounding the epidermis of Drosophila embryos triggers an instantaneous calcium wave that can travel, via gap junctions, several cell rows back from the wound edge. Blocking this calcium flash results in less hydrogen peroxide synthesis at wounds and fewer hemocytes being recruited to the wound site. I show that the wound triggered calcium wave stimulates DUOX to synthesise hydrogen peroxide through DUOX's calcium binding EF hands. Therefore, calcium influx represents the earliest known step in the wound inflammatory pathway. As well as recruiting innate immune cells , wounds in epithelia must be repaired to restore homeostasis of the tissue. Wound edge cells assemble an actomyosin "pursestring" that contracts the wound margin, and filopodia that knit the wound edges together. Many studies have focussed on these actin machineries at the leading edge of front row cells that recapitulate the mechanisms leading to dorsal closure in Drosophila development. The role of cells back from the front row during wound repair is much less clear. Here, I show that cells several rows back from the leading edge not only stretch during wound closure, but also shrink their junctions with neighbours , leading to cell intercalation events that are related to how tissues become elongated during germ band extension in the embryo. Junction shrinking occurs in a pulsatile manner and is driven by flashes of actomyosin directed to the cell vertices of shrinking junctions by breaks in localisation of the cell polarity protein Par3/ Bazooka at cell vertices. Halting myosin activity inhibited junction shrinking leading to reduced wound edge advancement. Therefore, active remodelling of cell shape back from the front row is important for enabling the actomyosin cable to efficiently close the wound, and repair the epithelium
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available