Drosophila glutamate receptor RNA expression in embryonic and larval muscle fibers

Abstract

Glutamate is the excitatory transmitter at neuromuscular synapses in Drosophilu, and electrophysiological studies indicate that the receptors for glutamate are concentrated in muscle fibers at synaptic sites. Acetylcholine is the excitatory transmitter at vertebrate neuromuscular synapses, and previous studies have shown that accumulation of acetylcholine receptors (AChRs) at synaptic sites is controlled both by transcriptional and post-translational mechanisms. The transcriptional pathway culminates in selective expression of AChR subunit genes in nuclei near the synaptic site, causing AChR mRNA to accumulate in the synaptic region of the muscle fiber. We used a cDNA encoding a subunit of the Drosophila muscle glutamate receptor (DGluR-11) to determine the temporal and spatial expression pattern of the DGluR-I1 gene during embryogenesis and in larval muscle. We show that DGluR-I1 mRNA is first expressed at stage 12 of embryogenesis and that expression is detected in developing dorsal, lateral, and ventral somatic muscles within the next 2 hr. By stage 16 DGluR-I1 mRNA is expressed in all somatic muscles and in pharyngeal muscles. In third instar larvae DGluR-I1 mRNA is expressed in all body-wall muscle fibers. DGluR-I1 mRNA, however, is expressed throughout the larval muscle fibers and is not concentrated within muscle fibers at neuromuscular synapses. These results indicate that although the DGluR-I1 gene is expressed in somatic muscle cells it is not selectively expressed in nuclei near the synaptic site. o 1995 Wiley-Liss, Inc.

Drosophila glutamate receptor mRNA expression and mRNP particles

“…These results are consistent with a previous study by Currie et al that used In Situ Hybridization with DIG labeled RNA probes against GluRIIA followed by colorimetric detection and light microscopy. 24 Although the techniques of Currie et al could not reveal the small GluR mRNA aggregates that we observed, they definitely showed that GluRIIA was distributed throughout muscles, consistent with our results. A subsequent study by Sigrist et al using similar techniques focused on GluRIIA mRNA near NMJs, but did not explicitly claim that GluRIIA mRNA was found exclusively at NMJs.…”

“…22,23 However, it's unclear whether GluR mRNAs are preferentially localized near NMJs. A previous study by Currie et al (1995) suggests that GluRIIA is not localized. 24 However, the methods utilized in that study were not suitable for quantification, and did not permit visualization of mRNA aggregates or NMJs.…”

“…A previous study by Currie et al (1995) suggests that GluRIIA is not localized. 24 However, the methods utilized in that study were not suitable for quantification, and did not permit visualization of mRNA aggregates or NMJs. We therefore quantified GluRIIA, GluRIIB and GluRIIC mRNA signal intensity (average pixel value over the entire visible muscle surface).…”

Drosophila Syncrip modulates the expression of mRNAs encoding key synaptic proteins required for morphology at the neuromuscular junction

“…To date, studies have shown that GluRIIA mRNA aggregates are distributed throughout the muscle (Currie et al 1995;Karr et al 2009;Ganesan et al 2011). The Syp targets we have identified here, such as msp-300, hiw, nrx-1, α-spec, and dlg1, are now excellent candidates for localized expression at the NMJ.…”

Transmission, Development, and Plasticity of Synapses

“…GluR subunit transcripts are already expressed in the muscles at this time (Currie et al 1995;Petersen et al 1997;Marrus et al 2004;Qin et al 2005) and functional receptors are distributed throughout the muscle surface (Broadie and Bate 1993a;Nishikawa and Kidokoro 1995). GluRs then begin to cluster at nascent synapses, which requires innervation from the motor neuron (Broadie and Bate 1993a;Saitoe et al 1997).…”