Drosophila Strip serves as a platform for early endosome organization during axon elongation

Abstract

Early endosomes are essential for regulating cell signalling and controlling the amount of cell surface molecules during neuronal morphogenesis. Early endosomes undergo retrograde transport (clustering) before their homotypic fusion. Small GTPase Rab5 is known to promote early endosomal fusion, but the mechanism linking the transport/clustering with Rab5 activity is unclear. Here we show that Drosophila Strip is a key regulator for neuronal morphogenesis. strip knockdown disturbs the early endosome clustering and Rab5-positive early endosomes become smaller and scattered. Strip genetically and biochemically interacts with both Glued (the regulator of dynein-dependent transport) and Sprint (the guanine nucleotide exchange factor for Rab5), suggesting that Strip is a molecular linker between retrograde transport and Rab5 activation. Overexpression of an active form of Rab5 in strip mutant neurons suppresses the axon elongation defects. Thus, Strip acts as a molecular platform for the early endosome organization that plays important roles in neuronal morphogenesis.

The Strip-Hippo Pathway Regulates Synaptic Terminal Formation by Modulating Actin Organization at the Drosophila Neuromuscular Synapses

“…As we reported in our previous studies (Sakuma et al, 2014; Sakuma et al, 2015), one of the major roles of Strip is to regulate axon elongation. To investigate the role of Strip in synaptic development that occurred after axon elongation, we weakly knocked down strip specifically in motor neurons by using short hairpin RNA (The locations of the short hairpin RNA sequences on the strip molecular map is shown in Figure S1A).…”

“…Using an anti-Strip antibody (Sakuma et al, 2014), we found that Strip is localized at presynaptic sites adjacent to the neuronal membrane marker, HRP. It is excluded from the muscle subsynaptic reticulum (SSR), an in-folded membranous structure that contains many components including neurotransmitter receptors and the postsynaptic signaling complex, and was identified by Spectrin labeling (Figures 1A and 1B).…”

“…Mutants of Drosophila Mob4, a member of the core STRIPAK complex and homolog of mammalian Mob3, show abnormal microtubule morphology at NMJs and muscles (Schulte et al, 2010). Furthermore, we previously reported that Strip forms a complex with Glued, the homolog of mammalian p150 Glued (Sakuma et al, 2014), a component of the dynactin complex required for dynein motor-mediated retrograde transport along microtubules. Strip also affects microtubule stability (Sakuma et al, 2015).…”

“…Beyond this, the A and C subunits of PP2A, Mob3, Mst3, Mst4, Ysk1, Ccm3, Strip1, and Strip2 form the core mammalian STRIPAK complex. We previously reported that Strip, the Drosophila homolog of mammalian Strip1 and 2, is involved in early endosome formation, which is essential for axon elongation (Sakuma et al, 2014). Building on these findings, we hypothesized that the Strip-Hpo pathway may also be involved in neuronal synaptic development.…”

Vps54 regulatesDrosophilaneuromuscular junction development and controls postsynaptic density composition via a Rab7-dependent mechanism

“…Membrane and transmembrane proteins are transported to axon terminals via a Rab11-dependent mechanism whereas Rab5 and Rab7 are involved in local recycling and retrograde transport back to the soma (Jin et al, 2018; Khodosh et al, 2006). In Drosophila , a loss-of-function mutation in Rab5 causes defects in axon elongation in olfactory projection neurons and sensory neurons (Sakuma et al, 2014; Satoh et al, 2008). Mutations in Rab7 linked to Charcot-Marie-Tooth2b disease cause axon growth and guidance defects in fly sensory neurons (Ponomareva et al, 2016).…”