Investigating the direct effects of SSNA1 on microtubules

By Emily Overway

Headshot of Marija Žanić. She is wearing a blue top with a red-beaded necklace that has circular ornaments.
Marija Žanić, Ph.D.

The lab of Marija Žanić, professor of cell and developmental biology, is investigating the regulation of microtubules. Work led by former postdoctoral fellow Elizabeth Lawrence, recently published in eLife, details the role of microtubule-associated protein SSNA1 in microtubule stabilization and damage detection.

We sat down with Lawrence to learn more about this interesting work.

What issue/problem does your research address?
Sjögren’s syndrome nuclear autoantigen-1, or SSNA1, is a microtubule-associated protein with important functions in cilia, dividing cells, and developing neurons. Despite the importance of the protein, the direct effects of SSNA1 on microtubules were not known.

What was unique about your approach to the research?
We wanted to determine the direct effects of SSNA1 on microtubules. To do this, we used purified proteins and single-molecule total internal reflection fluorescence microscopy to reconstitute microtubule dynamics in vitro. TIRF microscopy is particularly suitable for our studies, as it ensures a high signal-to-noise ratio and limits any photodamage to our microtubules that may occur during imaging.

Headshot of Elizabeth Lawrence. She is wearing a dark blouse and brown-and-tan striped sweater.
Elizabeth Lawrence, Ph.D.

What were your findings?
The regulation of microtubule stability and turnover is essential for proper cellular function, but microtubules are subjected to damage due to mechanical forces, actions of molecular motors, and microtubule-associated proteins. We demonstrate that SSNA1 is both a potent microtubule stabilizer and a novel sensor of microtubule damage. Damage to the microtubule lattice is now understood to modulate the dynamics of the microtubule polymer. Thus, SSNA1 regulates microtubule dynamics both directly and via detecting sites of microtubule damage. We predict that these effects of SSNA1 on microtubules are critical for SSNA1’s function in developing neurons, dividing cells, and cilia.

What do you hope will be achieved with the research results in the short and long terms?
Our work sheds important mechanistic insight into the effects of SSNA1 on microtubule dynamics. In the longer term, we envisage that this will lead to a more complete understanding of the cellular roles of SSNA1 in cilia, dividing cells, and neurons.

What are the benefits of this research?
SSNA1 is implicated in Sjögren’s syndrome, which is a highly prevalent autoimmune disease that predominantly affects women starting in their mid-40s. A greater understanding of SSNA1 activity could help in developing new treatments for Sjogren’s syndrome patients.

Where is this research taking you next?
Having identified SSNA1 as a novel sensor of microtubule damage, we’re interested in exploring how microtubule damage is regulated and repaired. In the future we plan to further investigate the interplay between SSNA1 and microtubule-severing enzymes, which can actively damage microtubules in cells. We’re also really excited to investigate how the activities of microtubule-stabilizing proteins (such as SSNA1) and severing proteins are coordinated to regulate and remodel the microtubule network.

This work was funded by the National Institutes of Health and the National Science Foundation.