Genetically Modified Mosquitoes

While pursuing my PhD at the Johns Hopkins Bloomberg School of Public Health, I worked with Dr. George Dimopoulos on various aspects of mosquito immunity. Dr. Dimopoulos had acted as Dr. Xi's post-doctoral mentor prior to Dr. Xi moving to Michigan State University, meaning that a lot of the skills I learned during my Master's degree transferred directly into the experiments I would be doing with Dr. Dimopoulos. Consequently, I was able to hit the ground running while working on my PhD and quickly make multiple novel observations about the Anopheles mosquitoes I began studying.

Physiological changes brought about by genetic upregulation of the mosquito immune system

Dr. Dimopoulos' group focuses on the ways that the mosquito immune system can be used to help control vector-borne disease. While there are many projects going on in the laboratory, including projects on dengue virus and various aspects of the mosquito microbiota, I began working on the ways in which the mosquito innate immune system controls infection by the Plasmodium parasites that cause human malaria. Previous members of the group had already created multiple strains of genetically modified Anopheles stephensi mosquitoes with greatly increased resistance to P. falciparum, and I set out to characterize those strains. I began by studying two specific strains with blood-meal inducible increased expression of the transcription factor Rel2. Rel2 is a positive regulator of the mosquito IMD immune pathway, and increased expression of Rel2 following a blood meal leads to a cascade of immune responses and killing of the parasite. I measured changes in the transcriptome and proteome of the mosquitoes following immune induction, allowing me to identify a large number of genes under the control of the IMD pathway. Further characterization of these genes led to the identification of novel anti-Plasmodium factors that are being studied further for their potential as targets for interrupting malaria transmission.

Fitness effects of short term immune activation on Anopheles stephensi mosquitoes

Multiple laboratory groups have created genetically modified mosquitoes with limited ability to spread human pathogens, but none of these mosquitoes have been released as part of vector-borne disease control programs. While the release of genetically sterilized Aedes aegypti males to reduce the mosquito population is a promising step forward for the use of genetically modified mosquitoes to control human disease, these differ fundamentally from those meant to replace the natural population. One reason for the delay in releasing a strain to replace wild-type mosquitoes with refractory mosquitoes hinges on concerns that the genetically modified mosquitoes will be less fit than the wild-type mosquitoes, and therefore will be unable to compete with them. I tested various aspects of mosquito fitness, including lifespan and fecundity under various conditions, and found no difference between wild-type and our genetically modified mosquitoes in the laboratory. Further, I saw that, under some circumstances, the genetically modified mosquitoes could have a mating advantage over wild-type mosquitoes. This advantage appears to be brought about by changes in the mosquito microbiota in response to the genetic modification, and represents the first observation of a genetically modified mosquito outcompeting wild-type mosquitoes.

My time with Dr. Dimopoulos was highly productive, and taught me a great many things. In addition to increasing my knowledge of molecular biology techniques such as DNA microarrays and iTRAQ, I was able to go on two field trips and gain experience working outside of the laboratory. I first went on a mosquito collecting trip to Puerto Rico with Dr. Dimopoulos and two fellow graduate students. We spent a week collecting mosquitoes, mostly from the genus Aedes, in order to learn more about the natural microbiota of wild mosquitoes. Later in my thesis work, I spent a month working with Dr. Kevin Kobylinski and the entomology group at the Armed Forces Research Institute of Medical Sciences in Bangkok. There, I taught the entomologists how to perform RNA interference and adult injections while testing the effects of the mosquito immune system on Plasmodium vivax infection in the mosquitoes. While my results were largely inconclusive, it was a great opportunity to learn to work in a resource limited setting, and to work with human samples for the first time.

To learn more about the research in Dr. Dimopoulos' lab, check out his group website or that of his current postdoc Dr. Sarah M. Short.