College of Arts & Sciences

Jillian Saunders

School of Biomedical Engineering, Science, & Health Systems

Biomedical Engineering

Faculty Mentor: Dr. Michael Akins Biology

Molly Mitchell Co-Mentor

Fragile X granules localize near axonal plasma membranes independent of the Fragile X protein FMRP

Fragile X Syndrome (FXS) is the most common inherited form of autism and intellectual disability. FXS occurs when the FMR1 gene is silenced, resulting in a loss of Fragile X Mental Retardation Protein (FMRP), a key regulator of neuronal translation. FMRP is found in a variety of complexes, including the Fragile X Granule (FXG), which is found only in axons. Past work has identified the neuronal circuits and developmental windows in which FXGs are found but not the localization of FXGs within these axons. Axons in the spinal cord provide an ideal system to address this question: in contrast to the small diameter axons that predominate in the brain, many populations of spinal cord axons are large enough to resolve by light microscopy. We used confocal microscopy to address FXG localization in large axons and whether this localization is controlled by FMRP. We found that FXGs are not distributed randomly throughout axons, and instead are found almost exclusively in close proximity to the plasma membrane. Further, this localization is independent of FMRP as FXG position was the same in wild type and Fmr1 null axons. These findings suggest that FXGs regulate local translation in response to cues detected by cell surface receptors.