We research the various steps in RNA processing including transport and translation during normal development and aging of neurons, as well as during the onset and progression of disease. In addition to these basic studies we seek to identify therapeutic strategies for diseases linked to RNA and metabolic dysregulation in the nervous system. Our research utilizes a combination of genetic, molecular, bioinformatics and pharmacological approaches in Drosophila (fruit flies), cultured cells and patient tissues. This “fly-to-man” approach takes advantage of the powerful, genetically tractable fruit fly model to uncover molecular mechanisms that we can subsequently validate in patient tissues.
1. Translational control in glia-neural stem cell interactions
We have recently discovered a novel role for the RNA binding protein, FMRP, in neural stem cells exit from quiescence, a universal mechanism utilized by stem and progenitor cells across phyla. Furthermore, using tissue specific RNAi we found that FMRP’s requirement switches from neural stem cells to glial cells during early larval brain development. While the genes that control stem cell quiescence remain largely unknown, recent findings indicate that the insulin signaling pathway is involved. Specifically, glial cells secrete insulin like peptides (dILPs) and this results in the activation of the PI3K/AKT pathway in both glia and neural stem cells. Based on these recent findings we hypothesize that FMRP may control exit from quiescence by regulating the insulin signaling pathway. We are currently testing this hypothesis using a combination of molecular and genetic approaches in Drosophila.
2. Lethal giant larvae (Lgl) in neural development.
Using forward genetics in Drosophila we identified Lgl as a novel functional interactor of FMRP in neurons. This suggests that lgl may function in neuronal development, a role previously confounded by its requirement in neural stem cells. Preliminary data obtained in my laboratory indicate that loss of lgl results in abnormal neuromuscular junction synapses. Current experiments are aimed at determining whether Lgl is required pre- or post-synaptically at the neuromuscular synapse. The long-term goal of this project is to elucidate the role of the tumor suppressor Lgl in the developing nervous system. We are also testing candidate microRNAs (miRNAs) for their ability to mediate Lgl’s function in the nervous system.
3. Lgl – novel mechanisms for tumor suppression.
Lgl is a tumor suppressor in flies and existing reports suggest that it may also be involved in cancer progression in humans. Using Drosophila as a model we are pursuing the potential connection between Lgl and RNA regulation during tumorigenesis. Through genetic interaction experiments we found that lgl may function in the miRNA pathway. In addition, using miRNA microarrays we identified a small number of miRNAs that are misexpressed in lgl mutant brains and the eye neuroepithelium. To determine if human Lgl1 (Hugl1) acts as a bona-fide tumor suppressor in mammals, we are collaborating with Dr. Joyce Schroeder (AZ Cancer Center) to test Hugl1’s role in breast cancer. We hypothesize that the miRNAs we discovered to be misexpressed in the fly model may act as effectors of Lgl in both the nervous system and/or during tumor growth. To test this possibility, we are using a combination of fly genetics, human cancer cells and mouse models to determine whether these candidate miRNAs mediate Lgl’s role in tumorigenesis.
4. Gene and drug discovery in a Drosophila model of Amyotrophic Lateral Sclerosis (ALS).
The RNA binding protein TDP-43 has recently been implicated in ALS and FTLD both as a cause as well as a marker of pathology. We have developed a Drosophila model of ALS based on the RNA binding protein, TDP-43. Loss of function for TDP-43 in flies recapitulates the progressive loss of motor ability characteristic to ALS. The overexpression of wild-type and mutant TDP-43, which mimics the mutations found in patients, also recapitulate the neuronal loss and other aspects of ALS pathology, including motor neuron death, locomotor dysfunction and reduced survival. These tools will allow us to uncover the mechanisms leading to neuronal degeneration associated with ALS and other neurodegenerative disorders such as Alzheimer’s disease and Inclusion Body Myositis, where TDP-43 aggregates have been documented. We are currently performing a forward genetic screen and have already identified candidate chromosomal regions that modulate TDP-43’s neurotoxicity. We are also screening FDA approved drugs and small molecules to identify compounds that rescue the neurodegenerative phenotypes and locomotor defects in the fly model.
5. RNA regulation in heart development and disease
In collaboration with Dr. Carol Gregorio (Cellular and Molecular Medicine) we have begun to investigate RNA based mechanisms in the heart by studying the function of Fragile X Related Protein 1 (FXR1). We hypothesize that FXR1, the muscle specific homolog of FMRP functions in cardiac muscle by controlling the localized translation of specific mRNAs during myogenesis and also in response to stress. Using a candidate gene approach as well as microarray experiments, we have identified the first mRNA targets that are translationally controlled by FXR1 in the heart. These include components of the costamere complex and intercalated disc, both structurally and functionally important in the developing heart. Notably, mutations in several candidate targets have been previously implicated in cardiomyopathies, which led us to investigate links between FXR1 and human heart disease. We are also working to develop a Drosophila model of heart disease based on FXR1, which we will use to complement the mouse model. The long-term goal of this project is to elucidate the mechanisms for RNA regulation in the heart, which remains an understudied area of muscle biology.