Traffic最新文献

Localization of mRNA facilitates spatiotemporally controlled protein expression in neurons. In axons, mRNA transport followed by local protein synthesis plays a critical role in axonal growth and guidance. However, it is not yet clearly understood how mRNA is transported to axonal subcellular sites and what regulates axonal mRNA localization. Using a transgenic mouse model in which endogenous β-actin mRNA is fluorescently labeled, we investigated β-actin mRNA movement in axons of hippocampal neurons. We cultured neurons in microfluidic devices to separate axons from dendrites and performed single-particle tracking of axonal β-actin mRNA. Compared with dendritic β-actin mRNA, axonal β-actin mRNA showed less directed motion and exhibited mostly subdiffusive motion, especially near filopodia and boutons in mature dissociated hippocampal neurons. We found that axonal β-actin mRNA was likely to colocalize with actin patches (APs), regions that have a high density of filamentous actin (F-actin) and are known to have a role in branch initiation. Moreover, simultaneous imaging of F-actin and axonal β-actin mRNA in live neurons revealed that moving β-actin mRNA tended to be docked in the APs. Our findings reveal that axonal β-actin mRNA localization is facilitated by actin networks and suggest that localized β-actin mRNA plays a potential role in axon branch formation.

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common cause of familial and sporadic Parkinson's disease. A plethora of evidence has indicated a role for LRRK2 in endolysosomal trafficking in neurons, while LRRK2 function in glia, although highly expressed, remains largely unknown. Here, we present evidence that LRRK2/dLRRK mediates a lysosomal pathway that contributes to glial cell death and the survival of dopaminergic (DA) neurons. LRRK2/dLRRK knockdown in the immortalized microglia or flies results in enlarged and swelling lysosomes fewer in number. These lysosomes are less mobile, wrongly acidified, exhibit defective membrane permeability and reduced activity of the lysosome hydrolase cathepsin B. In addition, LRRK2/dLRRK depletion causes glial apoptosis, DA neurodegeneration, and locomotor deficits in an age-dependent manner. Taken together, these findings demonstrate a functional role of LRRK2/dLRRK in regulating the glial lysosomal pathway; deficits in lysosomal biogenesis and function linking to glial apoptosis potentially underlie the mechanism of DA neurodegeneration, providing insights on LRRK2/dLRRK function in normal and pathological brains.

Endomembrane system compartments are significant elements in virtually all eukaryotic cells, supporting functions including protein synthesis, post-translational modifications and protein/lipid targeting. In terms of membrane area the endoplasmic reticulum (ER) is the largest intracellular organelle, but the origins of proteins defining the organelle and the nature of lineage-specific modifications remain poorly studied. To understand the evolution of factors mediating ER morphology and function we report a comparative genomics analysis of experimentally characterized ER-associated proteins involved in maintaining ER structure. We find that reticulons, REEPs, atlastins, Ufe1p, Use1p, Dsl1p, TBC1D20, Yip3p and VAPs are highly conserved, suggesting an origin at least as early as the last eukaryotic common ancestor (LECA), although many of these proteins possess additional non-ER functions in modern eukaryotes. Secondary losses are common in individual species and in certain lineages, for example lunapark is missing from the Stramenopiles and the Alveolata. Lineage-specific innovations include protrudin, Caspr1, Arl6IP1, p180, NogoR, kinectin and CLIMP-63, which are restricted to the Opisthokonta. Hence, much of the machinery required to build and maintain the ER predates the LECA, but alternative strategies for the maintenance and elaboration of ER shape and function are present in modern eukaryotes. Moreover, experimental investigations for ER maintenance factors in diverse eukaryotes are expected to uncover novel mechanisms.

A GGGGCC (G₄ C₂ ) repeat expansion in the C9orf72 gene is the most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). Although disruptions in axonal transport are implicated in the pathogenesis of multiple neurodegenerative diseases, the underlying mechanisms causing these defects remain unclear. Here, we performed live imaging of Drosophila motor neurons expressing expanded G₄ C₂ repeats in third-instar larvae and investigated the axonal transport of multiple organelles in vivo. Expression of expanded G₄ C₂ repeats causes an increase in static axonal lysosomes, while it impairs trafficking of late endosomes (LEs) and dense core vesicles (DCVs). Surprisingly, however, axonal transport of mitochondria is unaffected in motor axons expressing expanded G₄ C₂ repeats. Thus, our data indicate that expanded G₄ C₂ repeat expression differentially impacts axonal transport of vesicular organelles and mitochondria in Drosophila models of C9orf72-associated ALS/FTD.

Plasmodium falciparum parasites which cause malaria, traffic hundreds of proteins into the red blood cells (RBCs) they infect. These exported proteins remodel their RBCs enabling host immune evasion through processes such as cytoadherence that greatly assist parasite survival. As resistance to all current antimalarial compounds is rising new compounds need to be identified and those that could inhibit parasite protein secretion and export would both rapidly reduce parasite virulence and ultimately lead to parasite death. To identify compounds that inhibit protein export we used transgenic parasites expressing an exported nanoluciferase reporter to screen the Medicines for Malaria Venture Malaria Box of 400 antimalarial compounds with mostly unknown targets. The most potent inhibitor identified in this screen was MMV396797 whose application led to export inhibition of both the reporter and endogenous exported proteins. MMV396797 mediated blockage of protein export and slowed the rigidification and cytoadherence of infected RBCs-modifications which are both mediated by parasite-derived exported proteins. Overall, we have identified a new protein export inhibitor in P. falciparum whose target though unknown, could be developed into a future antimalarial that rapidly inhibits parasite virulence before eliminating parasites from the host.

Since the discovery of lysosomes more than 70 years ago, much has been learned about the functions of these organelles. Lysosomes were regarded as exclusively degradative organelles, but more recent research has shown that they play essential roles in several other cellular functions, such as nutrient sensing, intracellular signalling and metabolism. Methodological advances played a key part in generating our current knowledge about the biology of this multifaceted organelle. In this review, we cover current methods used to analyze lysosome morphology, positioning, motility and function. We highlight the principles behind these methods, the methodological strategies and their advantages and limitations. To extract accurate information and avoid misinterpretations, we discuss the best strategies to identify lysosomes and assess their characteristics and functions. With this review, we aim to stimulate an increase in the quantity and quality of research on lysosomes and further ground-breaking discoveries on an organelle that continues to surprise and excite cell biologists.