TY - JOUR T1 - FMRP Regulates Neurogenesis <em>in Vivo</em> in <em>Xenopus Laevis</em> Tadpoles JF - eneuro JO - eneuro DO - 10.1523/ENEURO.0055-14.2014 SP - ENEURO.0055-14.2014 AU - Regina L. Faulkner AU - Tyler J. Wishard AU - Christopher K. Thompson AU - Han-Hsuan Liu AU - Hollis T. Cline Y1 - 2014/12/31 UR - http://www.eneuro.org/content/early/2015/01/23/ENEURO.0055-14.2014.abstract N2 - Fragile X Syndrome (FXS) is the leading known monogenic form of autism and the most common form of inherited intellectual disability. FXS results from silencing the FMR1 gene during embryonic development, leading to loss of Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein that regulates mRNA transport, stability, and translation. FXS is commonly thought of as a disease of synaptic dysfunction, however, FMRP expression is lost early in embryonic development, well before most synaptogenesis occurs. Recent studies suggest that loss of FMRP results in aberrant neurogenesis, but neurogenic defects have been variable. We investigated whether FMRP affects neurogenesis in Xenopus laevis tadpoles which express a homolog of FMR1. We used in vivo time-lapse imaging of neural progenitor cells and their neuronal progeny to evaluate the effect of acute loss or over-expression of FMRP on neurogenesis in the developing optic tectum. We complimented the time-lapse studies with SYTOX labeling to quantify apoptosis and CldU labeling to measure cell proliferation. Animals with increased or decreased levels of FMRP have significantly decreased neuronal proliferation and survival. They also have increased neuronal differentiation, but deficient dendritic arbor elaboration. The presence and severity of these defects was highly sensitive to FMRP levels. These data demonstrate that FMRP plays an important role in neurogenesis and suggest that endogenous FMRP levels are carefully regulated. These studies show promise in using Xenopus as an experimental system to study fundamental deficits in brain development with loss of FMRP and give new insight into the pathophysiology of FXS. Significance statement: Fragile X Syndrome (FXS) is commonly thought to arise from dysfunction of the synapse, the site of communication between neurons. However, loss of the protein which results in FXS occurs early in embryonic development, while synapses are formed relatively late. This suggests that deficits may occur earlier in neuronal development. We show that changes in FMRP expression in the brains of intact Xenopus laevis tadpoles have profound effects on neurogenesis, the generation of neurons. Therefore, neuronal function in FXS may be affected by events that have gone awry during embryonic development. These studies show promise in using Xenopus as a model of FXS and give new insight into the pathophysiology of FXS. ER -