Experimental demonstration of tethered gene drive systems for confined population modification or suppression

Abstract

Homing gene drives hold great promise for the genetic control of natural populations. However, current homing systems are capable of spreading uncontrollably between populations connected by even marginal levels of migration. This could represent a substantial sociopolitical barrier to the testing or deployment of such drives and may generally be undesirable when the objective is only local population control, such as suppression of an invasive species outside of its native range. Tethered drive systems, in which a locally confined gene drive provides the CRISPR nuclease needed for a homing drive, could provide a solution to this problem, offering the power of a homing drive and confinement of the supporting drive. Here, we demonstrate the engineering of a tethered drive system in Drosophila, using a TARE drive to support modification and suppression homing drives. Each drive was able to bias inheritance in its favor, and the TARE drive was shown to spread only when released above a threshold frequency in experimental cage populations. After the TARE drive had established in the population, it facilitated the spread of a subsequently released split homing modification drive (to all individuals in the cage) and of a homing suppression drive (to its equilibrium frequency). Our results show that the tethered drive strategy is a viable and easily engineered option for providing confinement of homing drives to target populations.

Finding the strongest gene drive: Simulations reveal unexpected performance differences betweenAnopheleshoming suppression drive candidates

“…Though the exact rate may be somewhat different due to differences in expression at distant genomic loci, such an experiment should still serve to confirm the presence and magnitude of this phenomenon. Batch effects could also have large effects on fecundity measurements 18 , which we have also noticed in our Drosophila experiments 32,33,37,38 . To address this, fecundity experiments should, when possible, be performed with individuals that were raised in the same container (and then subsequently separated by fluorescence, ideally for multiple generations) and preferably even from the same parent (though this is only a readily available option for split-drive systems, especially when drive conversion efficiency is very high, as achieved by most Anopheles drives).…”

A homing suppression gene drive with multiplexed gRNAs maintains high drive conversion efficiency and avoids functional resistance alleles

“…In some cases, this feature may be desirable if the drive should be strictly confined to a target population. Another way to achieve confinement that could still involve a homing suppression drive would be to use a tethered system in which the split homing element is linked to a confined modification drive system 70,71 . Such a method would also allow split homing suppression drive elements, similar to the one we tested, to potentially be release candidates if their performance is sufficient.…”

Modelling homing suppression gene drive in haplodiploid organisms

“…This may be undesirable in some situations such as targeted suppression of invasive populations. Tethered drive systems could provide a solution to this 48,49 and allow for confined drive in haplodiploids. Indeed, modelling shows that a TARE drive, which could be used to confine a homing drive that lacks Cas9, would perform well at an X-linked locus 46 , and it would have identical performance in haplodiploid species in other configurations 47 as well.…”