Drosophila melanogaster as a Model to Study the Multiple Phenotypes, Related to Genome Stability of the Fragile-X Syndrome

Fragile-X syndrome is one of the most common forms of inherited mental retardation and autistic behaviors. The reduction/absence of the functional FMRP protein, coded by the X-linked Fmr1 gene in humans, is responsible for the syndrome. Patients exhibit a variety of symptoms predominantly linked to the function of FMRP protein in the nervous system like autistic behavior and mild-to-severe intellectual disability. Fragile-X (FraX) individuals also display cellular and morphological traits including branched dendritic spines, large ears, and macroorchidism. The dFmr1 gene is the Drosophila ortholog of the human Fmr1 gene. dFmr1 mutant flies exhibit synaptic abnormalities, behavioral defects as well as an altered germline development, resembling the phenotypes observed in FraX patients. Therefore, Drosophila melanogaster is considered a good model to study the physiopathological mechanisms underlying the Fragile-X syndrome. In this review, we explore how the multifaceted roles of the FMRP protein have been addressed in the Drosophila model and how the gained knowledge may open novel perspectives for understanding the molecular defects causing the disease and for identifying novel therapeutical targets

dFmr1 Plays Roles in Small RNA Pathways of Drosophila melanogaster

Fragile-X syndrome is the most common form of inherited mental retardation accompanied by other phenotypes, including macroorchidism. The disorder originates with mutations in the Fmr1 gene coding for the FMRP protein, which, with its paralogs FXR1 and FXR2, constitute a well-conserved family of RNA-binding proteins. Drosophila melanogaster is a good model for the syndrome because it has a unique fragile X-related gene: dFmr1. Recently, in addition to its confirmed role in the miRNA pathway, a function for dFmr1 in the piRNA pathway, operating in Drosophila gonads, has been established. In this review we report a summary of the piRNA pathways occurring in gonads with a special emphasis on the relationship between the piRNA genes and the crystal-Stellate system; we also analyze the roles of dFmr1 in the Drosophila gonads, exploring their genetic and biochemical interactions to reveal some unexpected connections

Drosophila melanogaster as a model to study the role of FMRP protein, involved in the Fragile-X syndrome, in the piRNA-mediated genome stability

Fragile-X Syndrome represents the most common form of hereditary mental retardation. The disorder originates with mutations in the Fmr1 gene coding for the FMRP protein, which, with its paralogs FXR1 and FXR2, constitute a well-conserved family of RNA-binding proteins. The dFmr1 gene is the Drosophila ortholog of the human gene (Fmr1) involved in the syndrome (1). Drosophila melanogaster is considered a good model for the study of the molecular mechanism at the bases of the different phenotypes exhibited by patients. Drosophila has a unique fragile X-related gene, the dFmr1 gene, whose mutants exhibit defects in neuronal structure and function, behavior, and germline development, resembling those observed in patients (2,3). During the first part of the project, we identified and validated a new role for the dFmr1 gene in the silencing of transposable elements and repetitive sequences mediated by the piRNA pathway in the gonads (2,4-6). The starting point was the observation that the crystal-Stellate interaction (2), depending on a correct function of the piRNA pathway, was deregulated in dFmr1 mutants. We also demonstrated that dFmr1 interacts genetically and co-localizes with Aubergine and Vasa, two key components of the pathway. We also investigated in detail the genetic and physical interaction of dFmr1 in gonads, looking at the rescue of the “crystal phenotype” in testes and at the fertility of dFmr1 mutants in a genetic background overexpressing genes with a role in the piRNA pathway. These results will be useful for clarifying the role of dFmr1 in gonads and even in the nervous system (6-8). During the last part of the project we analyzed the possible role of the piRNA pathway in the nervous system, gaining information on its presence in this tissue and on the function of dFmr1 in the pathway. In addition, we started studying a possible physiological role of transposable elements during the brain development. Our research intends to clarify if a common molecular base is involved in the majority of the phenotypes exhibited by dFmr1 mutants due to genome instability

Expression of Transposable Elements in the Brain of the Drosophila melanogaster Model for Fragile X Syndrome

Fragile X syndrome is a neuro-developmental disease affecting intellectual abilities and social interactions. Drosophila melanogaster represents a consolidated model to study neuronal path-ways underlying this syndrome, especially because the model recapitulates complex behavioural phenotypes. Drosophila Fragile X protein, or FMRP, is required for a normal neuronal structure and for correct synaptic differentiation in both the peripheral and central nervous systems, as well as for synaptic connectivity during development of the neuronal circuits. At the molecular level, FMRP has a crucial role in RNA homeostasis, including a role in transposon RNA regulation in the gonads of D.m. Transposons are repetitive sequences regulated at both the transcriptional and post-transcriptional levels to avoid genomic instability. De-regulation of transposons in the brain in response to chromatin relaxation has previously been related to neurodegenerative events in Drosophila models. Here, we demonstrate for the first time that FMRP is required for transposon silencing in larval and adult brains of Drosophila “loss of function” dFmr1 mutants. This study highlights that flies kept in isolation, defined as asocial conditions, experience activation of transposable elements. In all, these results suggest a role for transposons in the pathogenesis of certain neurological alterations in Fragile X as well as in abnormal social behaviors

Alterazione dell'espressione dei geni orologio in Drosophila melanogaster aseguito di un intenso campo magnetico impulsato

Gli organismi hanno la capacità di percepire il campo magnetico terrestre e di alterare i processi biologici in risposta ad un campo magnetico applicato. Non sono ancora chiari i meccanismi molecolari alla base della percezione del campo magnetico. In questo lavoro abbiamo dimostrato che un campo magnetico impulsato di 400mT/1Hz induce un'alterazione comportamentale in individui adulti di Drosophila melanogaster. Inoltre, il livello di espressione di tim incrementa nelle teste dei moscerini dopo l'esposizione al campo. Tim è un target del magnetorecettore cryptochrome. Questi risultati preliminari indicano una possibile relazione tra il ritmo circadiano e cryptochrome nella percezione del campo magnetico

The RNA helicase BELLE Is involved in circadian rhythmicity and in transposons regulation in drosophila melanogaster

Circadian clocks control and synchronize biological rhythms of several behavioral and physiological phenomena in most, if not all, organisms. Rhythm generation relies on molecular auto-regulatory oscillations of interlocked transcriptional-translational feedback loops. Rhythmic clock-gene expression is at the base of rhythmic protein accumulation, though post-transcriptional and post-translational mechanisms have evolved to adjust and consolidate the proper pace of the clock. In Drosophila, BELLE, a conserved DEAD-box RNA helicase playing important roles in reproductive capacity, is involved in the small RNA-mediated regulation associated to the piRNA pathway. Here, we report that BELLE is implicated in the circadian rhythmicity and in the regulation of endogenous transposable elements (TEs) in both nervous system and gonads. We suggest that BELLE acts as important element in the piRNA-mediated regulation of the TEs and raise the hypothesis that this specific regulation could represent another level of post-transcriptional control adopted by the clock to ensure the proper rhythmicity