A Maternal Role for Mon1

Abstract

The complex of Mon1-Ccz1 functions as a GEF (Guanosine nucleoside exchange factor) for Rab7 and mediates the transition of Rab5 marked early endosomes to late endosomes. Drosophila Mon1 mutants have a shortened lifespan, have motor defects and are sterile. The egg chambers fail to mature resulting in stalling of oocytes at the previtellogenic stages. These defects can be rescued by expression of Dmon1 in the octopaminergic/tyraminergic neurons (DHIMAN et al. 2019). Eggs laid by neuronallyrescued Dmon1lof mutants fail to hatch into larvae indicating maternal roles for Dmon1. The cuticle pattern of these embryos shows absence of head structures and suggests a possible failure in axial patterning. We probed these embryos for spatiotemporal expression of A-P and D-V patterning genes using RNA in-situ hybridization. While D-V patterning genes, namely twist, snail, short-gastrulation and decapentaplegic show near normal patterns of expression, the A-P patterning genes nanos and oskar are mislocalised. This indicates that Dmon1 has a critical role in localising the determinants of the A/P axis in the egg. We hypothesize that this role may be related to Mon1’s function as a Rab converter.