Fragile X syndrome (FX), the most common heritable cause of mental retardation and autism, is a developmental disorder characterized by physical, cognitive, and behavioral deficits. FX results from a trinucleotide expansion mutation in the fmr1 gene that reduces levels of fragile X mental retardation protein (FMRP). Although research efforts have focused on FMRP's impact on mGluR signaling, how the loss of FMRP leads to the individual symptoms of FX is not known. Previous studies on human FX blood cells revealed alterations in the cyclic adenosine 3′, 5′-monophosphate (cAMP) cascade. We tested the hypothesis that cAMP signaling is altered in the FX nervous system using three different model systems. Induced levels of cAMP in platelets and in brains of fmr1 knockout mice are substantially reduced. Cyclic AMP induction is also significantly reduced in human FX neural cells. Furthermore, cAMP production is decreased in the heads of FX Drosophila and this defect can be rescued by reintroduction of the dfmr gene. Our results indicate that a robust defect in cAMP production in FX is conserved across species and suggest that cAMP metabolism may serve as a useful biomarker in the human disease population. Reduced cAMP induction has implications for the underlying causes of FX and autism spectrum disorders. Pharmacological agents known to modulate the cAMP cascade may be therapeutic in FX patients and can be tested in these models, thus supplementing current efforts centered on mGluR signaling.

Ferritin is a 24-subunit molecule, made up of heavy chain (HC) and light chain (LC) subunits, which stores and controls the release of dietary iron in mammals, plants, and insects. In mosquitoes, dietary iron taken in a bloodmeal is stored inside ferritin. Our previous work has demonstrated the transport of dietary iron to the ovaries via ferritin during oogenesis. We evaluated the localization of ferritin subunits inside CCL-125 [Aedes aegypti Linnaeus (Diptera: Culicidae), yellow fever mosquito] and 4a3b [Anopheles gambiae Giles (Diptera: Culicidae), African malaria mosquito] cells under various iron treatment conditions to further elucidate the regulation of iron metabolism in these important disease vectors and to observe the dynamics of the intracellular ferritin subunits following iron administration. Deconvolution microscopy captured 3D fluorescent images of iron-treated mosquito cells to visualize the ferritin HC and LC homologue subunits (HCH and LCH, respectively) in multiple focal planes. Fluorescent probes were used to illuminate cell organelles (i.e., Golgi apparatus, lysosomes, and nuclei) while secondary probes for specific ferritin subunits demonstrated abundance and co-localization within organelles. These images will help to develop a model for the biochemical regulation of ferritin under conditions of iron exposure, and to advance novel hypotheses for the crucial role of iron in mosquito vectors.

While the search for the genetic foundation of complex diseases receives a great deal of attention in the popular scientific press, it is merely the first step in a very long journey from gene identification to therapeutic options. Unexpectedly, even diseases that are caused by mutations in a single gene have a collection of diverse possible symptoms that variably affect each patient. What is becoming more obvious is the need to correlate specific endophenotypes, or subsets of disease symptoms, with specific genetic and/or environmental factors that differ from patient to patient. Surprisingly, Drosophila melanogaster, the common fruit fly, may be a key player in making these assignments, and in the drug-discovery process that necessarily follows. In this review, we discuss the issues that are emerging in neurological disease research, and why Drosophila’s role in the pathway towards pharmacological solutions is likely to increase.

Female mosquitoes are vectors for malaria, dengue fever, yellow fever and West Nile encephalitis. Mosquitoes must blood feed to complete oogenesis. Consequently, manipulating the iron metabolic pathway has the potential to interfere with mosquito fecundity, thereby decreasing vector numbers and disease transmission rates. The blood meal supplies high levels of heme and non‐heme iron which has the potential to create free radicals; however the animal appears to experience little ill effect. One possible protection from oxidative stress is iron storage in ferritin. Ferritin is a 24 subunit protein composed of heavy and light chains. We have shown that Aedes aegypti (yellow fever mosquito) larval cells exposed to high doses of iron secrete iron‐loaded ferritin into the culture medium and concentrate iron in the membrane fraction. Anopheles gambiae (African malaria mosquito) 4a3b larval cells are a hemocyte‐like cell line that is involved in immunity. We are interested in the interaction of iron metabolism and infection in these animals. We exposed 4a3b cells to high levels of iron. Similar to A. aegypti CCL‐125 cells, iron localizes in the membrane fraction. However, transcripts for the ferritin subunits, iron regulatory protein 1 and a putative DMT1 responded differently. These iron dose experiments in 4a3b cells lay the ground work to examine the relationship of iron metabolism and immunity in mosquitoes. This work was supported by funds from the National Institutes of Health (GM056812), the Agricultural Experiment Station, the College of Agriculture and Life Sciences and the BIO5 Institute for Collaborative Bioresearch at The University of Arizona.