Sex Bias and Sex Determination
Unlike female mosquitoes, which must drink blood in order to produce eggs, male mosquitoes do not bite people and thus cannot transmit pathogens to us. In collaboration with Dr. Zhijian Tu at Virginia Tech, my lab helped identify the genetic switch that controls whether a mosquito will be a male or female. Together, we proposed several potential ways this switch could be leveraged for sustained control of mosquito vectors. A major step in this direction came in 2020, when we confirmed that this switch is sufficient to generate fully fertile males from genetic females. Current work in my lab focuses on developing transgenic strains that express this switch conditionally, so that they may be reared as females or males depending on their diet or rearing conditions, an essential next step in developing a product that could be used in SIT or similar genetic approaches. In addition to a dominant sex factor, my lab is pursuing other methods of introducing sex bias or distorting sex ratios involving the selective editing of genes important in mosquito flight. In particular, we found that Ae. aegypti encodes both actin and myosin genes that are critical for female flight, but not males.
Mosquitoes do not get sick when infected with the same viruses that can kill or maim a human. I have been collaborating with Dr. Kevin Myles on this topic over a series of NIH-funded projects spanning more than 15 years. We have shown that arboviruses do indeed become pathogenic to their mosquito vectors when a critical part of their immune response is suppressed, and have built a molecular sensor to track how well this RNAi-based response is functioning in live adult mosquitoes. Using this sensor, we discovered that the RNAi immune response is compromised when mosquitoes are reared at lower temperatures, and that this is correlated with heightened susceptibility to arboviruses. Other work identified a role for piRNAs in antiviral immunity, substantial crosstalk between the RNAi and miRNA pathways. And clarified relationships amongst C-type lectins that might aid in the entry of viruses into cells. Currently, we are using CRISPR/Cas9 to better assess the specific role of Ae. aegypti genes in antiviral immunity. In addition to viruses, mosquitoes are also vectors of the parasites that cause malaria. Despite the requirement for parasites to invade the mosquito salivary gland, this process is poorly understood. Working with colleagues at the NIH, we have established a role for the salivary protein SGS1 in multiple stages of the malaria parasite life cycle, and helped identify a connection between hormonal signaling and immune cell development.
All life on earth must maintain the integrity of their genomes in order to survive. Mosquitoes are no exception, and the choice of methods used can influence genome structure, mutation rates, gene duplication and most recently, the effectiveness of gene editing and gene drive technologies. Ae. aegypti typically employs end-joining based repair machinery in place of machinery that relies on sequence homology from ectopic sources. As a result, targeted indel generation in Ae. aegypti using CRISPR/Cas9 based gene editing is highly efficient, while rates of targeted gene knock-in are substantially lower. However, some of the most promising gene drive strategies to achieve population replacement or reduction rely upon homology-based repair processes for their activity, with even a small amount of end-joining repair capable of generating drive-resistant alleles that can slow or stop gene drive efforts. Projects in my lab aim to determine genetic factors in the mosquito that are responsible for the choice and execution of these different forms of repair, and on using that knowledge to influence repair choice. In particular, we are pursuing strategies to increase the efficiency of inserting genetic material into the mosquito genome in a precise manner, as well as developing technologies to program the removal of transgenic sequences.
In order to produce eggs, female mosquitoes such as Ae. aegypti drink more than their body weight in blood. While some of the iron in the bloodmeal must be used as a nutrient that is deposited in eggs, most of it must be safely excreted to avoid potential toxicity, and the proteins involved in this process are largely unknown. Previous work in my lab has aimed to identify proteins that might be involved in binding up free heme during digestion, or in transporting iron or heme from the gut lumen into the cells of the midgut. Collectively, these studies have identified a large cohort of molecules with relatively small effect size, suggesting the process of iron absorption and detoxification in mosquitoes is highly redundant. Current work in my lab aims to better characterize some of the previously identified top candidates, as well as develop new screening approaches to identify additional molecules important for the processes of iron/heme detoxification.
Policy, Regulation, and Guidance on the Responsible Use of Biotechnology
The pursuit and development of novel biotechnologies to ameliorate otherwise intractable societal problems brings with it an equally urgent responsibility to ensure such technologies are used ethically. After the first CRISPR-based homing gene drives were developed in 2015, I provided guidance and input to a report prepared by the National Academies of Science Engineering and Medicine on laboratory containment and oversight of gene drive research, as well as to the J. Craig Venter Institute on challenges in governance. Since then, I have helped developed guidance for the development of standard operating procedures and containment recommendations, as well as outlined a risk assessment approach for insects modified to contain gene drive transgenes. As a member of the NExTRAC, I am currently working to provide additional recommendations to how NIH funds and oversees gene drive research. Additionally, in collaboration with the Office of Science and Technology Policy at the Bush School of Public Service, I am part of a NIFA-AFRI funded project to begin the process of determining important values related to the possible agricultural uses of gene drive technology in Texas.