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Updated: May 1, 2026
Analyzing Mitochondrial Transport and Morphology in Human Induced Pluripotent Stem Cell-Derived Neurons in Hereditary Spastic Paraplegia
Published on: February 9, 2020
A biophysical analysis of mitochondrial movement: differences between transport in neuronal cell bodies versus
Babu Reddy Janakaloti Narayanareddy1, Suvi Vartiainen, Neema Hariri
1Department of Developmental and Cell Biology, University of California Irvine, Irvine, CA, 92697, USA.
Abstract:
There is an increasing interest in factors that can impede cargo transport by molecular motors inside the cell. Although potentially relevant (Yi JY, Ori-McKenney KM, McKenney RJ, Vershinin M, Gross SP, Vallee RB. High-resolution imaging reveals indirect coordination of opposite motors and a role for LIS1 in high-load axonal transport. J Cell Biol 2011;195:193-201), the importance of cargo size and subcellular location has received relatively little attention. Here we address these questions taking advantage of the fact that mitochondria - a common cargo - in Drosophila neurons exhibit a wide distribution of sizes. In addition, the mitochondria can be genetically marked with green fluorescent protein (GFP) making it possible to visualize and compare their movement in the cell bodies and in the processes of living cells. Using total internal reflection microscopy coupled with particle tracking and analysis, we quantified the transport properties of GFP-positive mitochondria as a function of their size and location. In neuronal cell bodies, we find little evidence for significant opposition to motion, consistent with a previous study on lipid droplets (Shubeita GT, Tran SL, Xu J, Vershinin M, Cermelli S, Cotton SL, Welte MA, Gross SP. Consequences of motor copy number on the intracellular transport of kinesin-1-driven lipid droplets. Cell 2008;135:1098-1107). However, in the processes, we observe an inverse relationship between the mitochondrial size and velocity and the run distances. This can be ameliorated via hypotonic treatment to increase process size, suggesting that motor-mediated movement is impeded in this more-confined environment. Interestingly, we also observe local mitochondrial accumulations in processes but not in cell bodies. Such accumulations do not completely block the transport but do increase the probability of mitochondria-mitochondria interactions. They are thus particularly interesting in relation to mitochondrial exchange of elements.
Insights
Cargo size and location impede molecular motor transport in Drosophila neurons. Larger mitochondria move slower and shorter distances in neuronal processes, suggesting confinement effects. Hypotonic treatment alleviates this impediment.
Area of Science:
- Cell Biology
- Neuroscience
- Biophysics
Background:
- Intracellular transport relies on molecular motors carrying cargo.
- Factors like cargo size and subcellular location influencing transport are understudied.
- Mitochondria serve as a model cargo in Drosophila neurons, exhibiting size variation.
Purpose of the Study:
- To investigate the impact of mitochondrial size and subcellular location on intracellular transport.
- To quantify transport properties in relation to cargo size and neuronal compartments (cell body vs. processes).
- To explore potential mechanisms of transport impediment in confined cellular environments.
Main Methods:
- Utilized genetically marked (GFP) mitochondria in live Drosophila neurons.
- Employed total internal reflection microscopy and particle tracking analysis.
- Quantified mitochondrial velocity, run distance, and accumulation patterns.
Main Results:
- Mitochondrial transport in cell bodies showed minimal opposition.
- In neuronal processes, larger mitochondria exhibited reduced velocity and shorter run distances.
- Hypotonic treatment improved mitochondrial transport in processes, suggesting confinement-induced impedance.
- Observed localized mitochondrial accumulations in processes, increasing mitochondria-mitochondria interactions.
Conclusions:
- Mitochondrial size and neuronal process confinement significantly impede motor-mediated transport.
- These findings highlight the importance of the cellular environment in regulating intracellular cargo trafficking.
- Mitochondrial accumulations may play a role in inter-mitochondrial communication and element exchange.
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