A Presynaptic Regulatory System Acts Transsynaptically via Mon1 to Regulate Glutamate Receptor Levels in Drosophila

Abstract

Mon1 is an evolutionarily conserved protein involved in the conversion of Rab5 positive early endosomes to late endosomes through the recruitment of Rab7. We have identified a role for Drosophila Mon1 in regulating glutamate receptor levels at the larval neuromuscular junction. We generated mutants in Dmon1 through P-element excision. These mutants are short-lived with strong motor defects. At the synapse, the mutants show altered bouton morphology with several small supernumerary or satellite boutons surrounding a mature bouton; a significant increase in expression of GluRIIA and reduced expression of Bruchpilot. Neuronal knockdown of Dmon1 is sufficient to increase GluRIIA levels, suggesting its involvement in a presynaptic mechanism that regulates postsynaptic receptor levels. Ultrastructural analysis of mutant synapses reveals significantly smaller synaptic vesicles. Overexpression of vglut suppresses the defects in synaptic morphology and also downregulates GluRIIA levels in Dmon1 mutants, suggesting that homeostatic mechanisms are not affected in these mutants. We propose that DMon1 is part of a presynaptically regulated transsynaptic mechanism that regulates GluRIIA levels at the larval neuromuscular junction.

Dmon1andrab7interact to regulate glutamate receptor GluRIIA levels at the larvalDrosophilaneuromuscular junction

“…Dmon1 D181 mutants show elevated levels of GluRIIA at post-synaptic densities. On an average, the observed increase is nearly two-fold (Deivasigamani et al, 2015). An increase in GluRIIA levels was also observed in Dmon1 D181/156 animals ( Fig.…”

“…clear. An interesting point to be noted in this context is that DMon1 is released from the pre-synaptic compartment (Deivasigamani et al, 2015). While we cannot completely rule out the possibility of DMon1 and Rab7 having independent effects on GluRIIA, the evidence based on the genetic interaction between the two, and localization of DMon1 suggests that the DMon1-Rab7 complex probably regulates a secretory process that influences GluRIIA levels.…”

“…It showed non-complementation with Df(2L)9062 indicating that the mutation is likely to be in either Dmon1 or smog-two genes that are uncovered by the deficiency line. We crossed pog 1 to Dmon1 D181 and Dmon1 D129 mutants: the former carries a deletion restricted to the 3' region of Dmon1, while the latter has a deletion spanning the 3' of Dmon1 and 5' region of the adjacent smog gene (Deivasigamani et al, 2015). Non-complementation was observed in both cases indicating that a mutation is likely to be in Dmon1.…”

“…Flystocks: All stocks were maintained on regular cornmeal agar medium. pog 1 (Kind gift from S. Kerridge); Dmon1 D181 (Deivasigamani et al, 2015); The following stocks were obtained from the Bloomington Stock Centre: UAS-Rab7RNAi (#27051); UAS- phenotype was carried out as described in Deivasigamani et al, 2015.…”

“…The requirement of Dmon1 appears to be primarily neuronal, with neuronal knockdown of Dmon1 phenocopying the GluRIIA phenotype and expression of Dmon1 in neurons but not muscle, being able to rescue the mutant defects (Deivasigamani et al, 2015). The mechanism by which DMon1 regulates GluRIIA expression is not clear.…”