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The initiation of further development is fundamental to the infectious processes of parasitic nematodes. I have examined early developmental activation of Trichinella spiralis larvae during host invasion, with particular emphasis on gene regulation and the timing of events. Using a novel approach, changes in tissue specific transcriptional activity were observed in live larvae during the infectious process with the fluorescent nucleic acid dyes SYTO12 and acridine orange. Simultaneously, the metabolic switch from anaerobic metabolism, characteristic of the infective stage, to aerobic metabolism, as found in the enteral stages, was tracked by measuring activities of the key regulatory enzymes phosphoenolpyruvate carboxykinase and pyruvate kinase, as well as isocitrate dehydrogenase (NADP) activity, and used as a co-indicator for developmental activation. Both metabolic enzyme activities and transcription patterns were found to change in response to host death, liberation from the nurse cell, and exposure to components of the host stomach environment. The role of amphidial neurones in developmental regulation was examined using FITC based labelling, and at least part of the initial developmental processes were discovered to be under amphidial control. Changes to the surface properties of larvae during the process of infection were monitored using the fluorescent lipid probe PKH26, and gave evidence for temporal regulation of activation-related alterations of larval structure and/ or physiology. Further, RNA fingerprinting was carried out to identify specific genes associated with, or regulating, developmental activation. Some putatively differentially expressed transcripts were identified, but could not be completely characterised to date. The results give a clear indication that the activation processes of T. spiralis infective larvae occur at a much earlier time than previously thought, and are stimulated upon liberation of the larvae from the nurse cell inside the host stomach. Further, regulation of development appears to be under transcriptional control, and tissue specific transcription is initiated early during the infectious process, perhaps immediately after release from the nurse cell.

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No description available.