RESUMO
Fragile X mental retardation gene (FMR1) encodes an RNA binding protein that acts as a negative translational regulator. We have developed a Drosophila fragile X syndrome model using loss-of-function mutants and overexpression of the FMR1 homolog (dfxr). dfxr nulls display enlarged synaptic terminals, whereas neuronal overexpression results in fewer and larger synaptic boutons. Synaptic structural defects are accompanied by altered neurotransmission, with synapse type-specific regulation in central and peripheral synapses. These phenotypes mimic those observed in mutants of microtubule-associated Futsch. Immunoprecipitation of dFXR shows association with futsch mRNA, and Western analyses demonstrate that dFXR inversely regulates Futsch expression. dfxr futsch double mutants restore normal synaptic structure and function. We propose that dFXR acts as a translational repressor of Futsch to regulate microtubule-dependent synaptic growth and function.
Assuntos
Drosophila melanogaster/fisiologia , Proteínas Associadas aos Microtúbulos/metabolismo , Fatores de Crescimento Neural/metabolismo , Proteínas do Tecido Nervoso/metabolismo , Junção Neuromuscular/fisiologia , Proteínas de Ligação a RNA , Sinapses/fisiologia , Animais , Encéfalo/citologia , Encéfalo/fisiologia , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/genética , Eletrorretinografia , Potenciais Evocados/fisiologia , Voo Animal/fisiologia , Proteína do X Frágil da Deficiência Intelectual , Regulação da Expressão Gênica , Genes de Insetos , Humanos , Microscopia de Fluorescência , Proteínas Associadas aos Microtúbulos/genética , Dados de Sequência Molecular , Fatores de Crescimento Neural/genética , Proteínas do Tecido Nervoso/genética , Junção Neuromuscular/citologia , Neurônios/citologia , Neurônios/fisiologia , Técnicas de Patch-Clamp , Células Fotorreceptoras de Invertebrados/crescimento & desenvolvimento , Células Fotorreceptoras de Invertebrados/fisiologiaRESUMO
We have found two novel lipocalins in the fruit fly Drosophila melanogaster that are homologous to the grasshopper Lazarillo, a singular lipocalin within this protein family which functions in axon guidance during nervous system development. Sequence analysis suggests that the two Drosophila proteins are secreted and possess peptide regions unique in the lipocalin family. The mRNAs of DNLaz (for Drosophila neural Lazarillo) and DGLaz (for Drosophila glial Lazarillo) are expressed with different temporal patterns during embryogenesis. They show low levels of larval expression and are highly expressed in pupa and adult flies. DNLaz mRNA is transcribed in a subset of neurons and neuronal precursors in the embryonic CNS. DGLaz mRNA is found in a subset of glial cells of the CNS: the longitudinal glia and the medial cell body glia. Both lipocalins are also expressed outside the nervous system in the developing gut, fat body and amnioserosa. The DNLaz protein is detected in a subset of axons in the developing CNS. Treatment with a secretion blocker enhances the antibody labeling, indicating the DNLaz secreted nature. These findings make the embryonic nervous system expression of lipocalins a feature more widespread than previously thought. We propose that DNLaz and DGLaz may have a role in axonal outgrowth and pathfinding, although other putative functions are also discussed.