In two trials, using variations of well-established methods, observed feeding on dsRNA-expressing bacteria had no evident effect on viability, behavior, reproduction or embryonic development of the snail Biomphalaria glabrata, compared to feeding on bacteria carrying an empty expression plasmid. Attempts to detect bacterial dsRNA content were thwarted, so it remains unclear whether feeding RNAi works in B. glabrata. Further efforts will aim at assessing bacterial RNA content. Meanwhile, other workers have identified a promising approach to schistosomiasis vector snail population control.
About This Project
Schistosomiasis is a disease transmitted by snails, responsible for chronic illness of many millions of the world's poorest people, mainly in Africa. This project tests the efficacy of RNAi, a targeted genetic weapon, to kill the snails and thus curtail the spread of the disease. RNAi acts only on specific gene sequences, making it environmentally benign and preventing the evolution of resistance in snail populations. Importantly, this snail-killing material would be very cheap to produce.
Ask the ScientistsJoin The Discussion
What is the context of this research?
Schistosomiasis is a debilitating chronic disease afflicting many millions among the poorest people in over seventy tropical nations, mainly in sub-Saharan Africa. The parasitic flatworms (schistosomes) that cause the disease are transmitted by several species of aquatic snails. Where there are none of these snails, the parasite cannot be passed between humans. Chemical molluscicides (snail-killing poisons) played a large part in eradicating schistosomiasis in Japan and Tunisia. These poisons are however quite toxic to other wildlife and humans, and their widespread use is not recommended. Other approaches (parasite-killing drugs, draining wetlands) also have drawbacks. RNA interference (RNAi) is a new option for a 'magic bullet' against snails, cheap enough for large-scale use (1,2).
What is the significance of this project?
We are testing a new method to induce RNAi in snails. RNAi is a natural mechanism of specific gene inactivation: when an animal's body cells encounter double-stranded RNA (dsRNA) that closely matches one of the animal's own gene sequences, that gene gets temporarily shut down.
In many species, dsRNA ingested with food triggers an RNAi response throughout the body. This ‘feeding RNAi’ method is being widely explored as a method of pest control. Biomphalaria glabrata, a major snail vector of schistosomiasis, is susceptible to RNAi: even bathing snails in dsRNA solutions results in specific gene silencing in multiple tissues (3). The proposed study is aimed at finding out if feeding RNAi may be equally effective. If so, it could be a powerful weapon against snail populations.
What are the goals of the project?
Bacteria engineered to produce dsRNA matching several DNA sequences of essential snail genes will be incorporated (alive or dead) into yummy snail chow. Control chow will be made with non-snail DNA. Adult B. glabrata fed on these chows will be assessed for viability, egg-laying, and embryonic development of offspring. Successful gene inactivation should ultimately be lethal to offspring and adults. Further experiments will test feeding RNAi in conditions simulating the dry and rainy seasons common in tropical wetlands.
The most economical method for dsRNA production uses synthetic DNA made to order. B. glabrata gene fragments will be combined with an available expression vector designed for bacterial dsRNA production. The company doing this work charges a one-time fee for incorporating the plasmid backbone; subsequent insertion of any DNA sequence is cheap (nine cents per base pair plus $25). Once these constructs are made, we will transform them into the appropriate strain of E. coli and feed (live or killed) bacteria to snails, experimenting only with snail food recipes and snail feeding regimens.
The PI is invited to join the Cabernard lab at the University of Washington as a visiting scholar this summer. Access to this well-equipped lab will facilitate transformation of RNAse-deficient E. coli with synthetic plasmids, as well as enabling analysis of protein expression by Western blotting. Analysis of mRNA expression by qPCR will be outsourced to a company that provides this service.
Week 2 - Obtain DNA constructs
Weeks 3-4 - Transform bacteria, grow & freeze stocks
Weeks 5 - 10 - Prepare food, set up snails
Weeks 11 - 13 - ? Carry out assays
Then compile results and report
Jun 01, 2018
Jun 08, 2018
Jun 22, 2018
Transform bacteria, grow, freeze stocks
Aug 03, 2018
Prepare food, set up snails
Sep 28, 2018
Compile results, report
Meet the Team
Morgan Q. Goulding
I am a developmental cell biologist and a teacher of wide-ranging topics in biology. I am especially interested in cellular processes underlying the earliest steps in patterning animal body plans.
My doctoral research applied single-cell deletion and other microsurgical interventions in embryos of the sea snail Ilyanassa, revealing that cell contacts NORMALLY shift the plane of a specific cell's asymmetric division, preventing its daughter cell from developing EXCESS neurosensory organs. In connection with this study, I also compiled a description of the Ilyanassa embryo's spatiotemporal pattern of cell division up to the 84-cell stage, revealing in this species a widespread tendency toward increased complexity compared with analogous patterns in other kinds of snail embryo.
As a postdoctoral researcher, I extended my explorations of cellular mechanics in early development by using genetics and live cell imaging analysis to dissect the spatial regulation of forces that move centrosomes in the C. elegans zygote.
More recently I have continued exploring how early embryonic cell cycles are regulated in coordination with the earliest cellular decisions impacting developmental potential in gastropods, which offer unique advantages as a model system for this area of discovery.
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