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Microtubule-associated protein function: lessons from expression in Spodoptera frugiperda cells
1Harvard Medical School, Department of Medicine, Brigham and Women's Hospital, Boston.
Abstract:
The phenotypes induced by the expression of neuronal microtubule-associated proteins (MAPs) in Sf9 cells have provided data on the in situ function of these proteins. Both MAP2 and tau can induce long processes in Sf9 cells, and the processes contain bundles of microtubules. In both cases the microtubules are aligned with their plus ends distal. Tau expression usually induces a single process that is unbranched and of uniform caliber. Processes can form even when the cells are grown in suspension. Microtubules do not extend all the way to the tip; instead the terminal region contains an actin-rich meshwork. Taxol treatment of Sf9 cells also induces the assembly of microtubules into bundles but does not induce process formation in Sf9 cells. Therefore the in vitro properties of tau as a molecule capable of assembling, stabilizing, and bundling microtubules do not fully account for the in vivo ability of tau alone to transduce microtubule assembly into a change in cell shape. The morphological features of the processes induced by MAP2 differ in highly informative ways.
Insights
Neuronal microtubule-associated proteins (MAPs) like MAP2 and tau induce cell processes in Sf9 cells. However, tau’s in vitro properties don’t fully explain its in vivo cell shape changes.
Area of Science:
- Cell Biology
- Neuroscience
- Biochemistry
Background:
- Neuronal microtubule-associated proteins (MAPs) are crucial for neuronal structure and function.
- Understanding the in situ function of MAPs provides insights into cellular morphogenesis.
Purpose of the Study:
- To investigate the in situ function of neuronal MAPs, specifically MAP2 and tau, in Sf9 cells.
- To determine if the in vitro properties of tau fully explain its role in inducing cell shape changes.
Main Methods:
- Expression of neuronal MAPs (MAP2 and tau) in Sf9 insect cells.
- Microscopic analysis of induced cellular phenotypes, including process formation and microtubule organization.
- Comparison with Taxol-induced microtubule assembly.
Main Results:
- Both MAP2 and tau expression induced long, microtubule-bundle-containing processes in Sf9 cells.
- Tau typically induced a single, unbranched process, while MAP2 induced distinct morphological features.
- Microtubule plus ends were distal in induced processes; terminal regions were actin-rich.
- Taxol induced microtubule bundling but not process formation, indicating MAPs are necessary for shape change.
Conclusions:
- The in vitro properties of tau (assembly, stabilization, bundling) do not fully account for its in vivo ability to induce cell shape changes.
- MAP2 and tau exhibit distinct mechanisms in transducing microtubule assembly into altered cell morphology.
- Sf9 cells provide a valuable model for studying the in situ functions of neuronal MAPs.