Basargekar, A. S. | bioRxiv Science

bioRxiv2020

Dmon1 and rab7 interact to regulate glutamate receptor GluRIIA levels at the larval Drosophila neuromuscular junction.

Regulation of post-synaptic receptors plays an important role in determining synaptic strength and plasticity. The Drosophila larval neuromuscular junction (nmj) has been used extensively as a model to understand some of these processes. In this context, we are interested in the role of Drosophila Monensin sensitive protein 1 (DMon1) in regulating glutamate receptor (GluRIIA) levels at the nmj. Dmon1 is an evolutionarily conserved protein which, in complex with CCZ1, regulates the conversion of early endosomes to late endosomes through recruitment of Rab7. C-terminal deletion mutants of Dmon1 (Dmon1{Delta}181) exhibit lethality. The escapers have a short life span and exhibit severe motor defects. At the nmj, these mutants show a defects in synaptic morphology and a strong increase in glutamate receptor GluRIIA levels. The mechanism by which Dmon1 regulates GluRIIA is unclear. In this study, we have described the characterization the mutation in an EMS mutant referred to as pog1 and demonstrate this mutant to be an allele of Dmon1. Further, we have examined the role of rab7 in regulation the of GluRIIA. We show that similar to Dmon1, knock-down of rab7 using RNAi in neurons, and not muscles, leads to an increase in GluRIIA. Loss of one copy each of Dmon1 with rab7 leads to a synergistic increase in receptor expression. Further, overexpression of an activated Rab7 can rescue the GluRIIA phenotype observed in Dmon1{Delta}181 mutants. Together, these results highlight a neuronal role for Rab7 in GluRIIA regulation and underscores the important of the endo-lysosomal pathway in this process.

genetics↗

bioRxiv2019

FGFR/Heartless and Smog interact synergistically to negatively regulate Fog mediated GPCR signaling.

G-protein coupled receptor (GPCR) signaling triggered by Folded gastrulation (Fog) is one of the pathways known to regulate glial organization and morphogenesis in the embryonic CNS in Drosophila. Fog is best known for its role in epithelial morphogenesis during gastrulation. Here, the signaling pathway includes GPCRs Mist and Smog and the G-Protein Concertina (Cta) which activate downstream effectors to bring about cytoskeletal changes essential for cell shape change In this study, we identify molecular players that mediate and serve as important regulators of Fog signaling in the embryonic CNS. We find that while Cta is essential for Fog signaling neither receptors, Mist nor Smog mediates signaling in the CNS. On the contrary, we find that Smog functions as a negative regulator of the pathway. Surprisingly, Heartless which encodes a fibroblast growth factor receptor, also functions as a negative regulator of Fog signaling. Further, we find that both heartless and smog interact in a synergistic manner to regulate Fog signaling. This study thus identifies novel regulators of Fog signaling that may play an important role in fine-tuning the pathway to control cell morphogenesis. It also suggests the likelihood of there being multiple receptors for Fog that mediate and regulate signaling in a context specific manner. Author SummaryIn Drosophila, Folded gastrulation (Fog) functions as ligand that signals via GPCRs to regulate cell shape during gastrulation -one of the earliest events in embryogenesis. Here, Fog signals via receptors Mist and Smog to activate the G-protein Concertina to elicit change in cell shape. In the embryonic central nervous system (CNS) this pathway regulates shape and organization of glia important for functions such as insulation of neurons and synapses. The mechanism of Fog signal transduction in the CNS and its regulation is not well understood. We have sought to address these questions in our study. We find that Concertina is an essential factor for Fog signaling in the CNS but interestingly Mist is not. In contrast, Smog functions as a negative regulator such that loss of Smog enhances Fog signaling. A similar role is played by the receptor tyrosine kinase-Heartless. Interestingly, we find that Smog and Heartless interact as part of a common genetic network to regulate Fog signaling. Our results thus provide novel insights into the regulation of Fog signaling and shed light on how signaling can be fine-tuned in a context dependent manner to control cell shape change which plays a critical role during development and organ formation.

cell biology↗