Monensin Sensitive 1 Regulates Dendritic Arborization in Drosophila by Modulating Endocytic Flux.

Rohit Krishnan Harish,Shweta Tendulkar,Girish S Ratnaparkhi,Anuradha Ratnaparkhi,Senthilkumar Deivasigamani

doi:10.3389/fcell.2019.00145

Abstract

Monensin Sensitive 1 (Mon1) is a component of the Mon1:Ccz1 complex that mediates Rab5 to Rab7 conversion in eukaryotic cells by serving as a guanine nucleotide exchange factor for Rab7 during vesicular trafficking. We find that Mon1 activity modulates the complexity of Class IV dendritic arborization (da) neurons during larval development. Loss of Mon1 function leads to an increase in arborization and complexity, while increased expression, leads to reduced arborization. The ability of Mon1 to influence dendritic development is possibly a function of its interactions with Rab family GTPases that are central players in vesicular trafficking. Earlier, these GTPases, specifically Rab1, Rab5, Rab10, and Rab11 have been shown to regulate dendritic arborization. We have conducted genetic epistasis experiments, by modulating the activity of Rab5, Rab7, and Rab11 in da neurons, in Mon1 mutants, and demonstrate that the ability of Mon1 to regulate arborization is possibly due to its effect on the recycling pathway. Dendritic branching is critical for proper connectivity and physiological function of the neuron. An understanding of regulatory elements, such as Mon1, as demonstrated in our study, is essential to understand neuronal function.

Highlights

Dendritic arbors are complex neuronal structures with distinct morphological features (Cajal, 1999; Garcia-Lopez et al, 2010; Berry and Nedivi, 2017)
R.I, D.L, and D.BP were reduced significantly, while the reduction of D.A had lower statistical significance (‘∗’; Figure 1H). These results demonstrate that arborization of the Class IV da (CIVda) neurons during development is sensitive to the dose of Monensin Sensitive 1 (Mon1) with decrease in Mon1 function leading to increased branching, dendritic length and area while enhancement of Mon1 function leads to a decrease in the measured parameters
Since the activity of Rab5 and Rab11 strongly modulates arborization of CIVda neurons, we explored the nature of the interaction between these Rabs 5, 7, and 11 and Mon1 to uncover features of vesicular recycling that are important for CIVda morphogenesis (Figure 3 and Supplementary Figures S2C–H)

Summary

INTRODUCTION

Dendritic arbors are complex neuronal structures with distinct morphological features (Cajal, 1999; Garcia-Lopez et al, 2010; Berry and Nedivi, 2017). An intrinsic genetic program patterns the arbors using molecular processes that are distinct from those that make axons These are found to be dependent on both, internal as well as external cues (Parrish et al, 2007; Jan and Jan, 2010). Rab proteins are key regulators of intracellular trafficking Both endocytic and exocytic pathways are believed to contribute to dendrite growth and branching (Jan and Jan, 2010; Dong et al, 2015; Valnegri et al, 2015). We propose that in the context of the da neurons, Mon serves to balance the endocytic flux flowing through the endo-lysosmal and recycling pathways to regulate dendrite morphogenesis

RESULTS

DISCUSSION

MATERIALS AND METHODS

Findings

ETHICS STATEMENT