Genome modification technologies have been increasing steadily in recent years. With the exception of direct genome editing technologies (ZFNs, TALENs and CRISPRs) variously technologies for use in insects rely heavily on transposon platforms to move these technologies into target genomes. For example, phiC31 and other site-specific systems use transposons to move recombination sites into the target genome. Of course, there is also a lot of interest in just moving transgenes into insect genomes.
It has been clear for some time that we have available a robust collection of transposon-based integration systems that have very wide host ranges. Integration systems are not limiting the use of genome modification technologies in insects.
What limits the utility of integration systems is insects is delivering them to germ-line stem cells. To date the only approach that has been effective has been direct injection of appropriately aged insect embryos. Of course, post injection survival of those injected insects, maintenance of their fertility and their successful backcrossing are equally essential.
The use of genome modification technologies in the honeybee, Apis mellifera, are a great case in point.
Schulte et al. (2014) have managed to overcome those problems and successfully deliver piggyBac-based gene vectors that integrated efficiently and resulted in transgenics. They have not established colonies of transgenic honeybees but were able to show that G0 queens produced transgenic drones.
Of the 15 and 10 fertile queens produced in two reported experiments 4 and 2 produced transgenic progeny, respectively.
Schulte et al (2014) relied on an ‘off the shelf’ piggyBac system with a conventional 3xP3 based transgenic marker and a more customized marker based on AmAct5C. Their strategy for expressing piggyBac transposase is also fairly standard and involved supplying embryos with capped, polyadenylated transposase mRNA.
What was absolutely critical to the success of their effort was their deep knowledge of the biology of honeybees and an uncanny ability to manipulated honeybees in the laboratory so that existing genetic technologies could be deployed. It is a scenario seen often over the years with various insects but there is no doubt that honeybees presented a monumental challenge. That Schulte and collaborators were up to the task is a great credit to their skill and innovation.
This is a major accomplishment for which those working on honeybees should be thankful. While perhaps not easy, the path Schulte et al have blazed is a very important one.
This is a paper worth reading by anyone interested in insect genetic technologies.
Christina Schulte, Eva Theilenberg, Marion Müller-Borg, Tanja Gempe, and Martin Beye
Highly efficient integration and expression of piggyBac-derived cassettes in the honeybee (Apis mellifera) PNAS 2014 ; published ahead of print May 12, 2014, doi:10.1073/pnas.1402341111
IGTRCN Participant, Yehuda Ben-Shahar contributed a very nice perspective article in PNAS to accompany the Schulte et al. paper. This is also worth a look, he puts the work in a useful context.