Cell Biology and Anatomy

Our long-term research interests lie in elucidating the molecular basis for cell polarity and how cellular asymmetry controls diverse processes ranging from neural development and synapse remodelling to cell division, growth and differentiation. To address these significant biological questions we are using a combination of genetic, cell biological and biochemical approaches in Drosophila melanogaster and various cell culture models. The following research projects are currently being pursued in the lab: 1) mRNA transport in neural development and disease. Fragile X syndrome (FraX) is the most common form of inherited mental retardation and is due to loss of function for the FMR1 gene, which encodes an RNA-binding protein (FMRP). FMRP is thought to function in neurons by controlling the transport and local translation of target mRNAs, however its requirement for the localization of target mRNAs has remained elusive. To test the role of FMRP in mRNA transport, we have developed a genetically encoded mRNA imaging system with which we can track mRNA live in cultured neurons. These experiments demonstrate that FMRP acts as a regulator of transport for mRNA granules in developing neurons and suggest that defects in transport may contribute to FraX. Future directions include in vivo studies of mRNA transport in neurons and the role of mRNA targeting in normal development and disease.  2) Novel genes involved in the Fragile X pathway. We recently conducted a dominant modifier genetic screen in Drosophila to identify novel genes that interact with the fly FMR1 (dFmr1) during development and found, among others, 19 alleles of lgl, a tumor suppressor known to control cell polarity. Through a combined genetic and molecular approach we found that Lgl functions upstream of FMRP to control neural development in flies. In addition, Lgl and FMRP form a complex, which contains mRNA and is conserved in mammals. These data suggest a model whereby Lgl controls the localization of FMRP/mRNA complexes in neurons and we are currently testing this possibility. Future experiments will address the molecular mechanisms underlying Lgl function in controlling the distribution of RNA granules in developing neurons. In addition, other genes identified in the screen are currently being mapped and further characterized. 3) Fragile X and stem cells. We are investigating the role of FMRP in neural stem cells using larval neuroblasts as a model system and have preliminary evidence that FMRP may control stem cell proliferation and differentiation. Current experiments include a combination of immunostaining for cell cycle and cell fate markers in conjunction with flow cytometry as well as clonal analyses in the brain to dissect the precise role of FMRP in stem cells. In the future, we aim to identify the mRNA targets which mediate the function(s) of FMRP in stem cells. 4) Fragile X proteins in heart development. We have recently started a collaboration with Dr. Gregorio’s laboratory to determine the possible role of translational control in cultured cardiomyocytes under normal conditions and under stress. 5) Lgl in neural development. We identified Lgl as a novel interactor of Fragile X protein using forward genetics. Currently, we are investigating the role of Lgl in neurons,  a function previously confounded by its requirement in early development. Experiments are being conducted to determine the mechanisms of Lgl function in neural and synaptic development. 6) Lgl – mechanisms for tumor suppression. Lgl is a tumor suppressor in flies and some evidence suggests that it may be required for cancer progression in humans. To test if human Lgl (Hugl1) may be involved in human cancers, we knocked down Hugl1 in a colon cancer cell line and are currently performing in vitro invasion assays as well as animal experiments to test if loss of Hugl1 function results in increased metastasis. Future experiments will focus on identifying the molecular mechanisms by which Lgl contributes to tumorigenesis using a combination of fly genetics and cancer cell models.