Vps54 regulates Drosophila neuromuscular junction development and interacts genetically with Rab7 to control composition of the postsynaptic density

Molecular mechanism on autophagy associated cardiovascular dysfunction in Drosophila melanogaster

As a highly conserved cellular process, autophagy has been the focus of extensive research due to its critical role in maintaining cellular homeostasis and its implications in cardiovascular pathogenesis. The decline in muscular function, along with the neuronal system, and increased sensitivity to stress have been recognized in multiple animal models. Autophagic defects in cardiovascular architecture and cellular dysfunction have been linked to both physiological and pathological conditions of the heart in mammals and Drosophila. In this review, we systematically analyze the autophagy-associated pathways in the hearts of fruit flies and aim to provide a comprehensive understanding for developing potential treatments for patients and effective strategies for agricultural applications. This analysis elucidates the molecular mechanisms of autophagy in cardiovascular function under both physiological and pathological conditions in Drosophila, offering significant insights into the development of cardiovascular diseases. The loss of key autophagy-associated proteins, including the transmembrane protein Atg9 and its partners Atg2 or Atg18, along with DmSestrin, leads to cardiac hypertrophy and structural abnormalities in Drosophila, resembling the age-dependent deterioration of cardiac function. Members of the autophagy-related (Atg) gene family, cellular or nuclear skeletal lamins, and the mechanistic or mammalian target of rapamycin (mTOR) signaling pathways are critically influential in heart function in Drosophila, with autophagy activation shown to suppress cardiac laminopathy. The mTORC1/C2 complexes, along with axis of Atg2-AMPK/Sirt1/PGC-1α pathway, are essential in the hearts of both mammals and fruit flies, governing cardiac development, growth, maturation, and the maintenance of cardiac homeostasis. The beneficial effects of several interventions that enhance cardiac function, including exercise and cold stress, can influence autophagy-dependent TOR activity of the serine/threonine protein kinase signaling in both mammals and Drosophila. Exercise has been shown to increase autophagy when it is deficient and to inhibit it when it is excessive, highlighting the dual role of autophagy in cardiac health. This review evaluates the functional significance of autophagy in the heart, particularly in the context of Drosophila, in relation to mTORC-associated autophagy and the axis of Atg2-AMPK/Sirt1/PGC-1α pathways. It systematically contrasts the molecular mechanisms underlying autophagy-related cardiovascular physiological and pathological conditions in both fruit flies and mammals. The evolutionary conservation of autophagy underscores the value of Drosophila as a model for understanding broader mechanisms of autophagy across species. This study not only deepens our understanding of autophagy's role in cardiovascular function but also provides a theoretical foundation for the potential application of autophagy in agricultural pest control.

FMRP cooperates with miRISC components to repress translation and regulate neurite morphogenesis in Drosophila

Fragile X Syndrome (FXS) is the most common inherited form of intellectual disability and is caused by mutations in the gene encoding the Fragile X messenger ribonucleoprotein (FMRP). FMRP is an evolutionarily conserved and neuronally enriched RNA-binding protein (RBP) with functions in RNA editing, RNA transport, and protein translation. Specific target RNAs play critical roles in neurodevelopment, including the regulation of neurite morphogenesis, synaptic plasticity, and cognitive function. The different biological functions of FMRP are modulated by its cooperative interaction with distinct sets of neuronal RNA and protein-binding partners. Here, we focus on interactions between FMRP and components of the microRNA (miRNA) pathway. Using the Drosophila S2 cell model system, we show that the Drosophila ortholog of FMRP (dFMRP) can repress translation when directly tethered to a reporter mRNA. This repression requires the activity of AGO1, GW182, and MOV10/Armitage, conserved proteins associated with the miRNA-containing RNA-induced silencing complex (miRISC). Additionally, we find that untagged dFMRP can interact with a short stem-loop sequence in the translational reporter, a prerequisite for repression by exogenous miR-958. Finally, we demonstrate that dFmr1 interacts genetically with GW182 to control neurite morphogenesis. These data suggest that dFMRP may recruit the miRISC to nearby miRNA binding sites and repress translation via its cooperative interactions with evolutionarily conserved components of the miRNA pathway.

Role of GARP Vesicle Tethering Complex in Golgi Physiology

The Golgi associated retrograde protein complex (GARP) is an evolutionarily conserved component of Golgi membrane trafficking machinery that belongs to the Complexes Associated with Tethering Containing Helical Rods (CATCHR) family. Like other multisubunit tethering complexes such as COG, Dsl1, and Exocyst, the GARP is believed to function by tethering and promoting fusion of the endosome-derived small trafficking intermediate. However, even twenty years after its discovery, the exact structure and the functions of GARP are still an enigma. Recent studies revealed novel roles for GARP in Golgi physiology and identified human patients with mutations in GARP subunits. In this review, we summarized our knowledge of the structure of the GARP complex, its protein partners, GARP functions related to Golgi physiology, as well as cellular defects associated with the dysfunction of GARP subunits.

The GARP complex prevents sterol accumulation at the trans-Golgi network during dendrite remodeling

Membrane trafficking is essential for sculpting neuronal morphology. The GARP and EARP complexes are conserved tethers that regulate vesicle trafficking in the secretory and endolysosomal pathways, respectively. Both complexes contain the Vps51, Vps52, and Vps53 proteins, and a complex-specific protein: Vps54 in GARP and Vps50 in EARP. In Drosophila, we find that both complexes are required for dendrite morphogenesis during developmental remodeling of multidendritic class IV da (c4da) neurons. Having found that sterol accumulates at the trans-Golgi network (TGN) in Vps54KO/KO neurons, we investigated genes that regulate sterols and related lipids at the TGN. Overexpression of oxysterol binding protein (Osbp) or knockdown of the PI4K four wheel drive (fwd) exacerbates the Vps54KO/KO phenotype, whereas eliminating one allele of Osbp rescues it, suggesting that excess sterol accumulation at the TGN is, in part, responsible for inhibiting dendrite regrowth. These findings distinguish the GARP and EARP complexes in neurodevelopment and implicate vesicle trafficking and lipid transfer pathways in dendrite morphogenesis.

Vps54 Regulates Lifespan and Locomotor Behavior in Adult Drosophila melanogaster

Vps54 is an integral subunit of the Golgi-associated retrograde protein (GARP) complex, which is involved in tethering endosome-derived vesicles to the trans-Golgi network (TGN). A destabilizing missense mutation in Vps54 causes the age-progressive motor neuron (MN) degeneration, muscle weakness, and muscle atrophy observed in the wobbler mouse, an established animal model for human MN disease. It is currently unclear how the disruption of Vps54, and thereby the GARP complex, leads to MN and muscle phenotypes. To develop a new tool to address this question, we have created an analogous model in Drosophila by generating novel loss-of-function alleles of the fly Vps54 ortholog (scattered/scat). We find that null scat mutant adults are viable but have a significantly shortened lifespan. Like phenotypes observed in the wobbler mouse, we show that scat mutant adults are male sterile and have significantly reduced body size and muscle area. Moreover, we demonstrate that scat mutant adults have significant age-progressive defects in locomotor function. Interestingly, we see sexually dimorphic effects, with scat mutant adult females exhibiting significantly stronger phenotypes. Finally, we show that scat interacts genetically with rab11 in MNs to control age-progressive muscle atrophy in adults. Together, these data suggest that scat mutant flies share mutant phenotypes with the wobbler mouse and may serve as a new genetic model system to study the cellular and molecular mechanisms underlying MN disease.