standard Conditional Lethal Mutations for Insect Control

Rachel Wiltshire

Rachel Wiltshire is a Ph.D. student in Biological Sciences at the University of Notre Dame.
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In a recently published paper in Science Bulletin, Lin and Wang (2015) created RIDL (release of insects carrying a dominant lethal) strains of D. melanogaster using RNAi against the Pygopus (Pygo) gene – a PHD-finger protein playing an essential role in signaling during embryogenesis and imaginal disc development and when mutated halts development of juvenile stages.

Lin and Wang (2015), like other researchers are exploring the use of genetically modified insects that are detrimental to the growth of natural populations of insects of both agricultural and medical importance; an exploration of growing importance as insects continue to evolve strategies that thwart current control interventions.

Lin and Wang (2015) created two plasmid constructs, yp1-tTA (Drosophila yolk protein 1 – tetracycline-controlled transactivator) and tetO-PygoIR (a Pygo inverted-repeat silencing transgene responsive to tetracycline), and used them to transform  Drosophila w1118 .  After creating eighteen recombinant lines and making various crosses to test expression of lethality and effectiveness of sterility, two homozygous lines, XD11 and XD15, were selected for further study.

A Model for the role of Pygopus (Pygo) .  Image from Inés Carrera et al. PNAS 2008;105:6644-6649 ©2008 by National Academy of Sciences

A Model for the role of Pygopus (Pygo) .
Image from Inés Carrera et al. PNAS 2008;105:6644-6649
©2008 by National Academy of Sciences

The lethal effect of silencing Pygo expression in the F1 progeny of XD11 and XD15 in the absence of tetracycline was validated by transferring larvae hatched within the previous 24 hours on tetracycline-containing diet, to vials containing diet with or without tetracycline. No live first instar larvae; pupae or adults emerged from the tetracycline-free vials demonstrating that XD11 and XD15 strains are effectively lethal in the absence of tetracycline.  Unexpectedly the authors reported no sex-specific lethality even with the use of the sex-specific yp1 promoter.

Autocidal and Sterile Insect Control.

Autocidal and Sterile Insect Control.

To test the efficiency of RNAi-induced lethality, outcrosses of XD11, XD15 and wild-type males were maintained separately on diet with or without tetracycline. Each was independently crossed with wild-type females that were allowed to oviposit on diet.  Lin and Wang observed a significant difference between the numbers of transgenic progeny surviving to adulthood compared to wild-type in the tetracycline-free environment thus, demonstrating high penetrance within heterozygous progenies that could be exploited for population suppression or elimination.

Longevity of the RNAi-based RIDL system was tested by comparing the survival of XD11 and XD15 against wild type on diet with and without tetracycline. Survival data demonstrate that the lifespan of the transgenic lines are as long as wild type or long on both diets indicating that disruption of the Pygo gene at the adult stage does not decrease longevity and potentially increases fitness thus, enhancing effective delivery of the lethal gene into wild populations.

The promising results of this study demonstrate that a RNAi-based RIDL system, which disrupts conserved early-acting genes and signaling pathways critical for development, might be exploited for control of a wide range of medically and economically important insect species.

 Xinda Lin, Guanlin Wang  2015.  Development of a RNAi-based release of insects carrying a dominant lethal (RIDL) system in Drosophila melanogaster. Sci. Bull. 60(3):356-362 doi 10.1007/s11434-014-0667-x

 

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