Elucidation of the Role of miR-184 in the Development and Maintenance of the Drosophila Melanogaster Nervous System

Abstract

MicroRNAs (miRNAs) are short, non-coding RNA sequences that are generated from longer primary transcripts (pri-miRNA). These pri-miRNAs are processed by the endonuclease Drosha into a hairpin secondary structure (pre-miRNA), exported from the nucleus and cleaved by the enzyme Dicer to form a duplex RNA molecule. This miRNA:miRNA* duplex is subsequently further processed to form a single-stranded, mature miRNA. miRNAs have been extensively characterized and are known to play important roles in various physiologic and pathologic pathways. One hallmark of miRNAs function is their ability to modulate the downstream activities of protein-coding genes, as well as various other aspects of gene expression, by acting as post-transcriptional repressors of their messengerRNA (mRNA) targets. miR-184 is a highly conserved miRNA gene expressed in the Drosophila nervous system throughout development; and has been shown to target key regulators of differentiation, proliferation and apoptosis. Here we identify a novel role for miR-184 in regulating the development and maintenance of the Drosophila melanogaster post-embryonic nervous system. We present evidence which suggest miR-184 targets (i) paralytic (para), a voltage-gated sodium channel, shown to control neuronal excitability; and (ii) tramtrack69 (ttk69), a transcription factor known to regulate glial cell number and fate determination during embryonic development. In the absence of miR-184, homozygous loss-of-function mutant adult flies demonstrate hyperactive episodes in response to mechanical shock, indicative of increased susceptibility to seizures. Homozygous loss-of-function mutants also exhibit shortened lifespan, as well as reduced group longevity. Additionally, miR-184 deficient mutant larvae exhibit abnormal development of glia and glial progenitors; while expression of miR-184 exclusively in glia - reversed polarity- (repo) expressing cells - up-regulates development of glial cells. Phenotypes of the adult loss-of-function mutant are suppressed by genetic loss of para function; while larval phenotypes are rescued by reducing the genetic dosage of ttk69. These data imply that miR-184 functions to control post-embryonic gliogenesis, as well as in maintaining neuronal excitability and integrity of the Drosophila aging brain.