Fragile X syndrome, the most common form of inherited mental retardation and leading genetic cause of autism, is caused by transcriptional silencing of the Fmr1 gene. The fragile X mental retardation protein (FMRP), the gene product of Fmr1, is an RNA binding protein that negatively regulates translation in neurons. The Fmr1 knock-out mouse, a model of fragile X syndrome, exhibits cognitive deficits and exaggerated metabotropic glutamate receptor (mGluR)-dependent long-term depression at CA1 synapses. However, the molecular mechanisms that link loss of function of FMRP to aberrant synaptic plasticity remain unclear. The mammalian target of rapamycin (mTOR) signaling cascade controls initiation of cap-dependent translation and is under control of mGluRs. Here we show that mTOR phosphorylation and activity are elevated in hippocampus of juvenile Fmr1 knock-out mice by four functional readouts: (1) association of mTOR with regulatory associated protein of mTOR; (2) mTOR kinase activity; (3) phosphorylation of mTOR downstream targets S6 kinase and 4E-binding protein; and (4) formation of eukaryotic initiation factor complex 4F, a critical first step in cap-dependent translation. Consistent with this, mGluR long-term depression at CA1 synapses of FMRP-deficient mice is exaggerated and rapamycin insensitive. We further show that the p110 subunit of the upstream kinase phosphatidylinositol 3-kinase (PI3K) and its upstream activator PI3K enhancer PIKE, predicted targets of FMRP, are upregulated in knock-out mice. Elevated mTOR signaling may provide a functional link between overactivation of group I mGluRs and aberrant synaptic plasticity in the fragile X mouse, mechanisms relevant to impaired cognition in fragile X syndrome.

Fragile X syndrome is a leading heritable cause of mental retardation that results from the loss of FMR1 gene function. A Drosophila model for Fragile X syndrome, based on the loss of dfmr1 activity, exhibits phenotypes that bear similarity to Fragile X-related symptoms. Herein, we demonstrate that treatment with metabotropic glutamate receptor (mGluR) antagonists or lithium can rescue courtship and mushroom body defects observed in these flies. Furthermore, we demonstrate that dfmr1 mutants display cognitive deficits in experience-dependent modification of courtship behavior, and treatment with mGluR antagonists or lithium restores these memory defects. These findings implicate enhanced mGluR signaling as the underlying cause of the cognitive, as well as some of the behavioral and neuronal, phenotypes observed in the Drosophila Fragile X model. They also raise the possibility that compounds having similar effects on metabotropic glutamate receptors may ameliorate cognitive and behavioral defects observed in Fragile X patients.

Medical Sciences. In the article "Activation of protein kinase C correlates with a cardioprotective effect of regular ethanol consumption" by Masami Miyamae, Manuel M. Rodriguez, S. Albert Camacho, Ivan Diamond, Daira Mochly-Rosen, and Vincent M. Figueredo, which appeared in number 14, July 7, 1998, of Proc. Natl. Acad. Sci. USA (95, 8262-8267), the following correction should be noted. On page 8264, an incorrect Fig. 1 was printed. The correct figure and its accompanying legend are reproduced below.Neurobiology. In the article "Caspase-1 is activated in neural cells and tissue with amyotrophic lateral sclerosis-associated mutations in copper-zinc superoxide dismutase" by Piera Pasinelli, David R. Borchelt, Megan K. Houseweart, Don W. Cleveland, and Robert H. Brown, Jr., which appeared in number 26, December 22, 1998, of Proc. Natl. Acad. Sci. USA (95, 15763-15768), the following corrections should be noted. An erroneous version of Fig. 6 was published. The lane indicated as G41D represents lumbo-sacral spinal cord extract from G85R transgenic mice. In Fig. 7a, cell viability is expressed as % of untreated cells and not as % of viability. FIG. 1. LVDP prior to 45 min of global ischemia and during reperfusion in four groups of perfused guinea pig hearts (n ϭ 9 for each group): 1, following 8 wk 15% ethanol-derived calories (E); 2, pair-fed controls (‚); 3, following 8 wk of ethanol, before and after 10 mM chelerythrine (F); and 4, pair-fed controls, before and after chelerythrine (s). LVDP recovery is significantly greater in hearts from ethanol-treated animals (P Ͻ 0.05 at each 6-min interval). Chelerythrine abolished ethanol's protective effect on LVDP recovery. Data are presented as mean Ϯ SEM (SEM not included for group 2 but lie well within SEM of groups 3 and 4). Physiology 3330Corrections Proc. Natl. Acad. Sci. USA 96 (1999)

Fragile X mental retardation is a prominent genetic disorder caused by the lack of the FMR1 gene product, a known RNA binding protein. Specific physiologic pathways regulated by FMR1 function have yet to be identified. Adult dfmr1 (also called dfxr) mutant flies display arrhythmic circadian activity and have erratic patterns of locomotor activity, whereas overexpression of dFMR1 leads to a lengthened period. dfmr1 mutant males also display reduced courtship activity which appears to result from their inability to maintain courtship interest. Molecular analysis fails to reveal any defects in the expression of clock components; however, the CREB output is affected. Morphological analysis of neurons required for normal circadian behavior reveals subtle abnormalities, suggesting that defects in axonal pathfinding or synapse formation may cause the observed behavioral defects.

We have evaluated the role of the Drosophila mushroom bodies (MBs) in courtship conditioning, in which experience with mated females causes males to reduce their courtship toward virgins (Siegel and Hall, 1979). Whereas previous studies indicated that MB ablation abolished learning in an olfactory conditioning paradigm (deBelle and Heisenberg, 1994), MB-ablated males were able to learn in the courtship paradigm. They resumed courting at naive levels within 30 min after training, however, while the courtship of control males remained depressed 1 hr after training. We also describe a novel courtship conditioning paradigm that established long-term memory, lasting 9 days. In MB-ablated males, memory dissipated completely within 1 day. Our results indicate that the MBs are not required for learning and immediate recall of courtship conditioning but are required for consolidation of short-term and long-term associative memories.