A recent report by Li et al. demonstrates that by using a state-of-the-art CRISPR/Cas9 genome editing, it is now possible to study the function of Orco in the locust, Locusta migratoria . The gene odorant receptor co-receptor (Orco) encodes an essential component of the olfactory receptor complex in insects. Yet, linking its action to specific behavioral and physiological phenotypes has been limited to a few genetically tractable insect species. This report by Li et al. is an important addition to the growing list of “non-model” insect species with edited genomes such as butterflies, mosquitos, and now locusts.
This blog was written by Yehuda Ben-Shahar, Ph.D. and Alexis Hill, Ph.D.
The successful editing of the locust genome is particularly important for both basic and agricultural research. Locusts display striking phase polyphenism, whereby solitary animals respond to increased population density by rapidly transitioning into a gregarious swarming phase. This phenomenon provides a powerful model for studying mechanisms of phenotypic plasticity in insects. Furthermore, in the swarming phase, locusts can become a serious agricultural threat, costing immense resources in lost crops and pest control efforts. As a model for basic biological research, the locust is also studied in the field of neuroscience due to the large size of its neurons, which are amenable to electrophysiological studies.
The study by Li et al. demonstrates that CRISPR/Cas9 based targeting of the Orco gene in the locust species Locusta migratoria led mostly to small 3-30 base pair chromosomal deletions, resulting mainly in frame shifts that are predicted to lead to null alleles. As expected, Li et al. demonstrate that the injected parental locusts were genetic chimeras, harboring multiple different somatic mutations. More importantly, they show that some chimeric injected parents carried germline mutations, which subsequently enabled the establishment of stable homozygous mutant genetic lines. In fact, the authors reported unusually high rates of CRISPR/Cas9-induced somatic and germline mutations, at 71.7% and 88.1% respectively. This high success rate indicates that the described protocol is very likely to enable the targeting of additional genes of interest in the locust genome.
As was previously reported in flies and mosquitoes, the successful genetic manipulation of the Orco gene in the locust was also associated with expected behavioral phenotypes, such as impaired olfactory neuronal activity, and odor-driven behaviors. These studies indicate that manipulations of genetic loci in the locust, and other previously genetically intractable insect species, has a great potential to expand our understanding of the genetic bases of behavior in diverse insect species that are important for both basic and applied biological research.
Li, Y, Zhang, J, Chen, D, Yang, P, Jiang, F, Wang, X, Kang, L. CRISPR/Cas9 in locusts: Successful establishment of an olfactory deficiency line by targeting the mutagenesis of an odorant receptor co-receptor (Orco). Insect Biochem. Mol. Biol. 2016; 79:27-35. doi: 10.1016/j.ibmb.2016.10.003