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A mitotic kinase scaffold depleted in testicular seminomas impacts spindle orientation in germ line stem cells
Heidi Hehnly1,2, David Canton1, Paula Bucko1
1Department of Pharmacology, Howard Hughes Medical Institute, University of Washington, Seattle, United States.
Abstract:
Correct orientation of the mitotic spindle in stem cells underlies organogenesis. Spindle abnormalities correlate with cancer progression in germ line-derived tumors. We discover a macromolecular complex between the scaffolding protein Gravin/AKAP12 and the mitotic kinases, Aurora A and Plk1, that is down regulated in human seminoma. Depletion of Gravin correlates with an increased mitotic index and disorganization of seminiferous tubules. Biochemical, super-resolution imaging, and enzymology approaches establish that this Gravin scaffold accumulates at the mother spindle pole during metaphase. Manipulating elements of the Gravin-Aurora A-Plk1 axis prompts mitotic delay and prevents appropriate assembly of astral microtubules to promote spindle misorientation. These pathological responses are conserved in seminiferous tubules from Gravin(-/-) mice where an overabundance of Oct3/4 positive germ line stem cells displays randomized orientation of mitotic spindles. Thus, we propose that Gravin-mediated recruitment of Aurora A and Plk1 to the mother (oldest) spindle pole contributes to the fidelity of symmetric cell division.
Insights
Gravin scaffolding protein and mitotic kinases Aurora A and Plk1 form a complex crucial for stem cell division. This complex, downregulated in seminoma, ensures correct spindle orientation, preventing cancer progression.
Area of Science:
- Cell Biology
- Molecular Oncology
- Stem Cell Biology
Background:
- Correct mitotic spindle orientation is vital for stem cell function and organogenesis.
- Spindle abnormalities are linked to cancer progression, particularly in germ line-derived tumors.
Purpose of the Study:
- To investigate the role of the scaffolding protein Gravin/AKAP12 in mitotic spindle orientation.
- To identify molecular mechanisms underlying spindle misorientation in germ line stem cells and seminoma.
Main Methods:
- Biochemical assays to characterize protein interactions.
- Super-resolution imaging to visualize spindle pole organization.
- Enzymology to study kinase activity.
- Gravin depletion and knockout mouse models.
Main Results:
- Identified a macromolecular complex of Gravin, Aurora A, and Plk1, downregulated in human seminoma.
- Gravin depletion led to increased mitotic index and disorganized seminiferous tubules.
- Gravin recruits Aurora A and Plk1 to the mother spindle pole, ensuring correct spindle orientation.
- Disruption of this axis caused mitotic delay and spindle misorientation, conserved in Gravin(-/-) mice.
Conclusions:
- Gravin acts as a scaffold to recruit Aurora A and Plk1 to the mother spindle pole.
- This Gravin-mediated complex is essential for the fidelity of symmetric cell division in stem cells.
- Dysregulation of this axis contributes to pathological spindle orientation observed in seminoma and Gravin deficiency.
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