Glutamate Receptor mRNA Expression and Regulation at the Drosophila Neuromuscular Junction.

摘要

Glutamate receptors (GluRs) mediate excitatory neurotransmission in the brain. The expression and localization of glutamate receptors in neurons is tightly regulated to achieve proper neurotransmission. As an example, mis-regulation of GluRs is associated with cognitive dysfunction in Alzheimer's disease. The regulatory mechanisms involved in expression and localization of GluRs are not fully understood. Particularly, regulation at the level of messenger RNA (mRNA) has not been extensively studied. Using the Drosophila melanogaster neuromuscular junction (NMJ) as a model synapse, I investigated sub-cellular distribution of GluR transcripts and mRNA regulation mechanisms.;Using fluorescence in situ hybridization to detect GluR subunit mRNA in the post-synaptic muscle fibers, it was observed that these mRNA appear as granule-like puncta resembling messenger ribonucleoprotein particles (mRNPs). These mRNPs had no sub-cellular enrichment and mRNPs of different subunits existed as distinct particles with no colocalization. By biochemical isolation of the GluRIIA subunit mRNPs, it was observed that GluRIIA mRNA was indeed associated with proteins. Peptide sequencing was used to identify mRNP-associated proteins. Genetically disrupting the expression of three of the identified genes, Vha44, CG12149 and CG17816 resulted in partial loss of GluRIIA protein at the NMJ. CG12149 and CG17816 are novel genes and were named optimus-prime (Opr) and bumblebee (Bmb), respectively. Further investigation of larvae with knockdown of Opr, revealed that Opr promotes GluRIIA expression at the mRNA level.