Graydon B. Gonsalvez - US grants

DESCRIPTION (provided by applicant): A contributing factor to a wide spectrum of human diseases is defective cell polarity. Many cell types use mRNA localization as a means to establish polarity. At present, there is a fundamental gap in our understanding of how mRNAs are localized in higher eukaryotes. The goal of this proposal is to address this gap in knowledge by determining the mechanism by which oskar and FMR1 mRNAs are localized. oskar mRNA is localized in Drosophila oocytes and FMR1 mRNA is localized in neurons. These transcripts are ideal candidates for study because although they are localized in different tissues, their localization utilizes many of the same factors. Thus, a common mechanism might operate to localize diverse mRNAs. Insights gained from these studies are therefore expected to be generally applicable to our understanding of mRNA localization. We propose to perform our studies using the Drosophila melanogaster model system. This model system will enable us to study the process of mRNA localization in the context of the whole organism. This study has three main objectives. The impetus for Aim 1 was our recent discovery that core proteins of the spliceosome known as Sm proteins have a role, outside of splicing, in mRNA localization. In the present study, we propose to determine the mechanism by which Sm proteins function in localizing oskar mRNA. In Aim 2, we propose to determine the mechanism by which oskar and FMR1 mRNA are coupled to motor proteins for transport. The primary motor implicated in transporting both mRNAs is Kinesin heavy chain (Khc). However, Khc does not use its canonical adaptor to bind to oskar and FMR1 mRNA. Thus, it is currently unknown how Khc binds to these transcripts. We hypothesize that an unknown adaptor links Khc to oskar and FMR1 mRNA. The goal of Aim 2 is to identify this unknown adaptor. Finally, Aim 3 centers on our unexpected finding that a separate motor, cytoplasmic Dynein, also functions in oskar mRNA localization. A function for Dynein in the localization of FMR1 mRNA has already been demonstrated. In this aim, we will precisely define the role of Dynein in transporting oskar mRNA. Furthermore, we will test the hypothesis that once Dynein delivers oskar mRNA to the posterior pole, it performs an additional function in maintaining asymmetric endocytic activity within the oocyte. Completion of these aims will significantly advance our understanding of how the cell builds a localization competent mRNP, and the mechanism by which that mRNP is coupled to motor proteins for transport. Ultimately, the knowledge gained from these studies will enable us to more effectively treat diseases that result from defective mRNA localization and cell polarity. )

? DESCRIPTION (provided by applicant): Undiagnosed diseases represent a significant burden to patients, their family, and the health care system of the United States. These diseases are hard to manage and even more difficult to treat because their underlying etiology is unknown. The objective of the National Institutes of Health Undiagnosed Disease Program (UDP) is to identify genomic abnormalities that are associated with these diseases. A patient that was part of the UDP program was found to harbor a missense mutation in the FAM109A gene. The patient presented with a range of symptoms including general developmental delay, motor deficit, sensory defects, and abnormal craniofacial and brain development. The goal of this proposal is to determine whether the patient mutation in FAM109A is directly responsible for the observed symptoms. FAM109A has been shown to associate with endocytic vesicles and to function in specific steps of vesicular sorting. However, the role of this gene has not been studied in vivo. In order to examine the causal link between the FAM109A mutation and disease symptoms, we propose to combine molecular studies in cell lines with genetic, physiological, and behavioral studies at the organismal level. The central hypothesis of this proposal is that the mutant FAM109A allele is defective in specific aspects of endocytic sorting, and that these defects directly correlate with patient symptoms. We will compare the ability of wild type versus mutant FAM109A to sustain endocytic sorting in cell culture models. In addition, we will generate a patient-mimetic mutation in the Drosophila and zebrafish homologs of FAM109A using CRISPR-mediated genome editing. Phenotypic analysis of mutant Drosophila and zebrafish will elucidate the in vivo roles of FAM109A and reveal whether the patient mutation is causal to the observed symptoms. Finally, we propose to examine whole genome sequencing databases to determine whether additional patients with developmental disorders harbor mutations in FAM109A.