Entomology at the Land Grant University: Perspectives from the Texas A&M University Department Centenary

23. Genetic Engineering of Insects: Current and Future Applications

C  Genetic Engineering of Insects Current and Future Applications
  Department of Entomology Texas A&M University–College Station The ability to genetically engineer and manipulate insect species holds great promise for the fields of agriculture and medicine. Genetic transformation technology will dramatically enhance our ability to investigate the basic biology of a number of insect species. This new information will undoubtedly lead to the identification of novel targets and control mechanisms for insects of agricultural and medical importance. It is also possible that genetically manipulated insects will be used directly to help control or modify insect pest populations. The goals of this chapter are to describe the current state of insect transformation and to predict some of the future applications of genetic transformation technology.    DROSOPHILA MELANOGASTER      The vinegar fly Drosophila melanogaster Meigen was first genetically transformed almost twenty years ago (Spradling and Rubin, ). Since that time, an immense volume of biological information has been produced as a result of genetic transformation studies performed on this model genetic organism. Studies in D. melanogaster that utilize genetic transformation technology continue to answer a vast array of biological questions pertaining to Drosophila development, behavior, physiology, and sex determination. In many cases the information obtained in the Drosophila system has been extrapolated directly to humans and resulted in the identification of a similar process, or lesion, in a human function or disease state. The successful development of a transformation system for D. melanogaster inspired several efforts to develop similar systems for insects of agricultural and medical importance. Unfortunately, for years this was a tale of many defeats and few triumphs, the reasons for which are discussed here. Thankfully , the number of insect species that have been successfully transformed is currently increasing at a rapid rate as shown in table .. A number of scientific advances have been primarily responsible for advancing the field of insect transformation. These include () an increase in the number and variety of transposable elements that are available; () the development of a nondestructive, autonomous, transformation marker gene; and () the use of plasmid-based mobility assays to assess transposable element function in target insects. It is likely that the number of researchers using transformation technology for investigations of insect biology will continue to increase as more improvements are made to existing systems.       All current examples of insect transformation have occurred through the use of transposable elements (TEs) of the type II class. These TEs are broadly characterized by the presence of short inverted terminal repeat sequences and an internally encoded transposase protein that can act in cis or trans to mobilize elements through a DNA only mechanism. The P element is one of the best-studied class II TEs and is the TE most commonly used for D. melanogaster transformation (Spradling and Rubin, ). However, when this TE was used for similar experiments in other insect species, no germline transformants were recovered, with one exception in the human malaria vector mosquito, Anopheles gambiae (Giles) (Miller et al., ). However, this was the result of a nonhomologous recombination event, occurred at a low frequency , and has not been replicated in other laboratories. Subsequent research demonstrated that the P element is not active in several insect species outside of Drosophila, presumably as a result of a requirement for host factors such as the inverted terminal repeat binding protein (Handler et al., ; Beall et al., ). The transient plasmid-based assays used to determine P element inactivity were adapted such that they could be      used to assess the ability of numerous TEs to excise and transpose in the embryonic soma of a number of non-drosophilid insects (Coates et al., ; Sarkar et al., ; Lobo et al., ; Catteruccia et al., ). At least four different transposable element systems are now available for non-drosophilid insect transformation.     The availability of a suitable genetic transformation marker gene is an essential component of a successful transformation system. The nature of transformation events dictates that injected individuals must be allowed to develop , mate, and produce progeny that can be identified as transgenic. The injected individuals themselves are not transgenic and those that will produce transgenic progeny cannot be identified at this stage are almost always in the minority and in some cases may be rare. This problem is further compounded as transgenic individuals tend to be the minority of the total siblings produced . The end result of these effects is that the number of transgenic individuals produced from...