Genetic Modifiers ofdFMR1Encode RNA Granule Components in Drosophila

Abstract

Mechanisms of neuronal mRNA localization and translation are of considerable biological interest. Spatially regulated mRNA translation contributes to cell-fate decisions and axon guidance during development, as well as to long-term synaptic plasticity in adulthood. The Fragile-X Mental Retardation protein (FMRP/dFMR1) is one of the best-studied neuronal translational control molecules and here we describe the identification and early characterization of proteins likely to function in the dFMR1 pathway. Induction of the dFMR1 in sevenless-expressing cells of the Drosophila eye causes a disorganized (rough) eye through a mechanism that requires residues necessary for dFMR1/FMRP's translational repressor function. Several mutations in dco, orb2, pAbp, rm62, and smD3 genes dominantly suppress the sev-dfmr1 rough-eye phenotype, suggesting that they are required for dFMR1-mediated processes. The encoded proteins localize to dFMR1-containing neuronal mRNPs in neurites of cultured neurons, and/or have an effect on dendritic branching predicted for bona fide neuronal translational repressors. Genetic mosaic analyses indicate that dco, orb2, rm62, smD3, and dfmr1 are dispensable for translational repression of hid, a microRNA target gene, known to be repressed in wing discs by the bantam miRNA. Thus, the encoded proteins may function as miRNA-and/or mRNA-specific translational regulators in vivo.

FMRP and Ataxin-2 function together in long-term olfactory habituation and neuronal translational control

“…Previous studies in Drosophila have indicated a broader role for Atx2 than dFmr1 in miRNA function in nonneuronal cells (31,80). Although Atx2 was necessary for optimal repression of four miRNA sensors examined in wing imaginal disk cells, dFmr1 was not necessary for repression of any of these sensors (31,80). The resulting conclusion that dFmr1 is required only for a subset of miRNAs The effect of dfmr1 and atx2 mutants on mRNP particles, marked by Me31B (magenta), in projection neuron cell bodies (B-E, green) and dendrites (G-J, green).…”

Drosophila DFMR1 Interacts with Genes of the Lgl-Pathway in the Brain Synaptic Architecture

“…By means of different approaches data were obtained on different mRNAs, interacting with FMRP (6,8,9,17,35,48,57). The physiological functions of few of them, though, have been validated in vivo (reviewed in 3, 10).…”

“…Among the most important mRNA targets of FMRP are: Fmr1 mRNA itself, microtubule associated protein 1b (MAP1b), postsynaptic density protein 95kDa (PSD-95), elongation factor 1a (EF1a), glutamate receptor subunits GluR1 and GluR2, activity-regulated cytoskeletal protein (Arc), tumor suppressor protein Lethal giant larvae (Lgl); translation regulators Dco/Dbt, PABP, Orb2, Rm62 and SmD3 (3,8,24,30,37,49,53,57 Much research has been focused on the role of FMRP as a translational regulator of specific synaptic proteins -presynaptic and postsynaptic (1, 19, 57, reviewed in 40).…”

“…By means of different approaches data were obtained on different mRNAs, interacting with FMRP (6,8,9,17,35,48,57). The physiological functions of few of them, though, have been validated in vivo (reviewed in 3, 10).Among the most important mRNA targets of FMRP are: Fmr1 mRNA itself, microtubule associated protein 1b (MAP1b), postsynaptic density protein 95kDa (PSD-95), elongation factor 1a (EF1a), glutamate receptor subunits GluR1 and GluR2, activity-regulated cytoskeletal protein (Arc), tumor suppressor protein Lethal giant larvae (Lgl); translation regulators Dco/Dbt, PABP, Orb2, Rm62 and SmD3 (3,8,24,30,37,49,53,57 Much research has been focused on the role of FMRP as a translational regulator of specific synaptic proteins -presynaptic and postsynaptic (1, 19, 57, reviewed in 40).A group of such important proteins are the scaffolding proteins, belonging to the Lgl-familyLgl, Dlg and Scrib. Scaffolding proteins organize the postsynaptic signal transduction machinery and coordinate the transport and clustering of receptors and other synaptic components on the postsynaptic membrane.…”

EGFP-FMRP Granules Are Proto-Granules That Can Be Shunted to Stress Granules During a Stress Response

“…Immunofluorescence studies have shown that these granules tend to be small and not that prevalent. In contrast, AFP-tagged FMRPs have been used by a number of laboratories to assess various questions concerning neuronal granule make up and dynamics (Antar et al, 2005;Barbee et al, 2006;Castren et al, 2001;Cziko et al, 2009;Darnell et al, 2005;De Diego Otero et al, 2002;Dictenberg et al, 2008;Levenga et al, 2009;Ling et al, 2004;Pfeiffer and Huber, 2007). These granules tend to be much larger than endogenous FMRP granules and also much more prevalent in dendrites.…”