Spatial and temporal constraints imposed on the hedgehog pathway by the primary cilium
Abstract/Contents
- Abstract
- Vertebrate Hedgehog (Hh) signaling requires the primary cilium, a microtubule-based organelle that projects from the cell surface and acts as a signaling antenna. Defects in cilium structure or function cause a range of Hh-related developmental disorders. Although much work has focused on understanding the mechanisms of Hh signal transduction in primary cilia, relatively little is known about how the cell biology of the organelle impacts its signaling capacity. Specifically, the primary cilium is a small organelle with respect to the total cell surface area, and it is a transient organelle with respect to the cell cycle. How do these spatial constraints and temporal dynamics of cilia affect how Hh signaling operates in developing tissues? To address this question, we developed new mammalian cell culture approaches to explore the spatial and temporal relationship between cilia and signal transduction. First, we used a medulloblastoma cell line to investigate how cilium transience during the cell cycle affects cells that require Hh pathway activity during the cell cycle to maintain proliferation. We show that cilia are competent for Hh signaling whenever they are present and that proliferative decisions are made in response to pathway activation in either the same cell cycle or the previous one. These results reveal that although the cilium is transient, Hh pathway control of the cell cycle is surprisingly robust. Next, we used these same cells to develop a screening approach to identify novel regulators of Hh signaling that are unique to proliferating cells. While our screen requires further optimization, our work reveals that screening for regulators of Hh pathway-dependent proliferation is a promising approach. Finally, we turned to the spatial constraint imposed by cilia, exploring how signaling operates when cilia only have access to a small proportion of the extracellular environment. We used polarized epithelial cultures in which basally-applied ligand could be spatially separated from apical cilia. We show that basally-applied ligand is not sufficient for signaling; apical ligand is necessary. These results suggest that in contexts where ligand is basal, there must be mechanisms to transport Hh ligand to the apical, ciliary compartment. Together, this work reveals that while cilia do impose spatial and temporal constraints on the Hh pathway, cells have mechanisms to ensure robust signaling during development. Further characterization of these mechanisms is an important goal of future work. It will also be interesting to expand these findings to other signaling pathways and functions of cilia in development beyond the Hh pathway
Description
| Type of resource | text |
|---|---|
| Form | electronic resource; remote; computer; online resource |
| Extent | 1 online resource |
| Place | California |
| Place | [Stanford, California] |
| Publisher | [Stanford University] |
| Copyright date | 2020; ©2020 |
| Publication date | 2020; 2020 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Author | Ho, Emily Kolenbrander |
|---|---|
| Degree supervisor | Stearns, Tim |
| Thesis advisor | Stearns, Tim |
| Thesis advisor | Fuller, Margaret T, 1951- |
| Thesis advisor | Nusse, Roel, 1950- |
| Thesis advisor | Oro, Anthony, 1958- |
| Degree committee member | Fuller, Margaret T, 1951- |
| Degree committee member | Nusse, Roel, 1950- |
| Degree committee member | Oro, Anthony, 1958- |
| Associated with | Stanford University, Department of Developmental Biology |
Subjects
| Genre | Theses |
|---|---|
| Genre | Text |
Bibliographic information
| Statement of responsibility | Emily Kolenbrander Ho |
|---|---|
| Note | Submitted to the Department of Developmental Biology |
| Thesis | Thesis Ph.D. Stanford University 2020 |
| Location | electronic resource |
Access conditions
- Copyright
- © 2020 by Emily Kolenbrander Ho
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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