Bio:

I am a PhD candidate studying the Aedes aegypti immune response to dengue virus (DENV) infection, with a focus on the role that the mosquito JAK-STAT pathway plays in controlling DENV replication and dissemination. My other projects include the characterization of tissue-specific transcriptomic responses to DENV infection in A. aegypti, and the identification and functional testing of candidate anti-viral effectors.

Current research:

With 50 million infections annually and approximately 2.5 billion people at risk in more than 100 countries, dengue has emerged as the world’s most important arboviral disease. The increasing spread of dengue virus (DENV) can in large part be attributed to the increasing geographic range of its mosquito vectors, Aedes aegypti and Aedes albopictus. Mosquitoes, like all insects, are exposed to a variety of microbes in their natural habitats, and possess an innate immune system that is capable of mounting a potent response against microbial challenge. I hope to contribute to our molecular understanding of the vector’s immune response to DENV, which will be essential for the development and evaluation of novel vector-targeted transmission control strategies.

1. Transgenic approach to understanding JAK-STAT pathway-mediated anti-DENV defense
The JAK-STAT pathway is an evolutionarily conserved pathway that has many roles in development, hematopoiesis, and immunity. Previous work from our group has shown that, in addition to the Toll and RNAi pathways, the JAK-STAT pathway plays a key role in the A. aegypti anti-DENV response: A. aegypti susceptibility to DENV infection increases when the JAK-STAT pathway is suppressed through RNAi-mediated knockdown of Dome and Hop. Conversely, mosquitoes become more resistant to DENV infection when PIAS, a negative regulator of the pathway, is silenced (Souza-Neto et al, 2009).
However, since relatively little is known about the molecular mechanisms by which this pathway acts to control virus replication, we are undertaking a transgenic approach to further characterize the biology of this pathway. I am currently generating transgenic A. aegypti lines that over-express JAK-STAT pathway components in response to blood-feeding, under the control of midgut- and fat body-specific promoters. These lines will enable us to study the spatio-temporal pattern of JAK-STAT pathway-mediated DENV resistance, and will also allow us to functionally test candidate effector genes by RNAI-mediated knockdown in a JAK-STAT-activated background.


Figure 1. (A) In the canonical JAK-STAT pathway, ligand binding to the receptor Dome triggers a conformational change that activates Hop, the receptor-associated Janus kinase. Activated Hop phosphorylates Dome, creating docking sites for the STAT transcription factors to bind. Once bound, STATs are phosphorylated, and are then able to dimerize and translocate to the nucleus, where they activate the expression of effector genes. DENV titers in the midguts of PIAS-, Hop-, and Dome-silenced mosquitoes at (B) 3 days and (C) 7 days post-infectious bloodmeal. *, p < 0.05 by Student’s t test (Souza-Neto et al, 2009).

2. Salivary gland-specific immune response to DENV infection
DENV infection of the mosquito salivary gland is essential for vertical pathogen transmission to vertebrates. In addition, mosquito saliva contains many substances with anti-clotting and vasodilatory properties that facilitate bloodmeal acquisition. In collaboration with Jose Ramirez, I am characterizing the A. aegypti salivary gland transcriptome, with the aim of identifying antiviral effectors that act specifically in this organ.

The transcriptional response to DENV infection was assessed in the salivary gland and carcass at 14 days post-bloodmeal. In addition, relative transcript abundance in the naïve SG and naïve carcass were also compared. Functional assays to determine the effect of candidate gene knockdown on DENV replication and mosquito blood-feeding propensity are currently underway.


Figure 2. (A) Venn diagram showing numbers of unique and commonly-regulated genes in the DENV-infected A. aegypti salivary gland (SG) and carcass at 14 days post-bloodmeal, and in the naive SG relative to carcass. (B) Functional classification of genes significantly regulated by DENV infection in the SG and carcass. UNK, unknown functions; DIV, diverse functions; MET, metabolism; RTT, replication, transcription, and translation; TRP, transport; CS, cytoskeletal and structural; PROT, proteolysis; DIG, blood and sugar food digestive; CSR, chemosensory reception; RSM, redox, stress and mitochondrion; IMM, immunity.

Publications:
Research articles
Sim S, Dimopoulos G. Dengue virus inhibits immune signaling in Aedes aegypti cells. PLoS ONE. 2010 May; 5(5): e10678.
 

Souza-Neto JA, Sim S, Dimopoulos G. An evolutionary conserved function of the JAK-STAT pathway in anti-dengue defense. Proc. Nat. Acad. Sci. USA. 2009 Oct;106(42):17841-17846.

Review articles
Cirimotich CM, Dong Y, Garver LS, Sim S, Dimopoulos G. Mosquito immune defenses against Plasmodium infection. Dev. Comp. Immunol. 2010 Apr;34(4):387-395.
Sim S, Ramirez JL, Dimopoulos G. Molecular discrimination of mosquito vectors and their pathogens. Expert Rev. Mol. Diagn. 2009;9(7):757-765.