MicroRNAs Is Associated With Drosophila Fragile X Mental Retardation Protein And Regulates The Circadian Rhythm In Brain And The Fate Of Germline Stem Cell In Ovary

Fragile X syndrome (FXS), one of the most common forms of inherited mental retardation, is characterized by mental retardation of variable severity, autistic behavior, macroorchidism in adult males, characteristic facial features, and hyperextensible joints. FXS is mainly caused by a massive CGG trinucleotide repeat expansion (usually more than 200) within the 5' untranslated region (UTR) of the fragile X mental retardation 1 gene (FMR1), which results in abnormal DNA methylation of both a nearby CpG island and the repeat itself, as a result, the transcription of FMR1 is silenced.In mammals, FMRP, along with its autosomal paralogs, the Fragile-X-Related Proteins FXR1P and FXR2P, compose a well conserved, small family of RNA-binding proteins (fragile X-related gene family) that share over 60% amino acid identity and contain two types of RNA-binding motifs: two ribonucleoprotein K homology domains (KH domains) and a cluster of arginine and glycine residues (RGG box). Unlike their mammalian counterparts, the fly genome harbors a single Fmr1 gene homolog, also referred to as dFmr1. Sequence comparisons show a high level of similarity between the functional domains of fly and mammalian Fmrp, with overall 56% similarity and 35% identity. FMRP was found to form a messenger ribonucleoprotein (mRNP) complex that associates with translating polyribosomes. It has been proposed that FMRP is involved in synaptic plasticity through the regulation of mRNA transportation and translation. The accumulated works from several groups suggest that FMRP could regulate the translation of specific mRNAs via the microRNA pathway.To understand the molecular pathogenesis of fragile X syndrome, both mouse and Drosophila models have been generated and extensively studied. Besides the deficits in learning and memory in these models, one consistent behavioral abnormality in these models is altered rhythms circadian behaviors, which potentially mimics the sleep abnormalities in the patients with fragile X syndrome. Circadian rhythm describes the approximately 24-hour cycles generated by a master pacemaker located in the suprachiasmatic nuclei (SCN) of the anterior hypothalamus of the mammalians and the ventral lateral neurons (LNvs) in Drosophila. Rhythms are manifest in such processes as locomotors activity and feeding behavior, sleep/wake patterns, and a variety of physiological and metabolic pathways. These circadian outputs are regulated by a central pacemaker, which receives environmental inputs and keeps circadian time. Although altered circadian rhythms were observed in both mouse and Drosophila models, however, the underling molecular mechanism remains elusive.Here we performed a series of gene expression analyses, including both mRNAs and microRNAs (miRNAs), and identified tens of genes and two miRNAs (miRNA-1 and miRNA-281) with altered expression in a circadian rhythms-dependent manner in dfmr1 mutant flies. Using immunoprecipitation assays, we showed that miR-1 and miR-281 are physically associated with dFMR1 in fly brain, suggesting that dFMR1 could modulate the biogenesis of these two miRNAs. These observations support a role of dFMR1 in the miRNA pathway, and suggest that the altered expression of selective miRNAs could contribute the circadian abnormalities associated with the loss of dFMR1 in fly.