In perpetually renewing tissues such as the vertebrate hair, proper growth and patterning requires precise interpretation of signaling cues between epithelial and mesenchymal components. One of the key regulators of hair follicle cycling is the secreted Sonic Hedgehog (Shh) morphogen. Shh activates a signaling pathway during the proliferative phase of the hair cycle to expand the hair follicle progenitors. Insufficient Shh signaling results in failure of the mature structure to emerge, while too much signaling results in excess progenitors and susceptibility to skin cancer. Clearly, spatial and temporal controls must be in place in order for this process to function properly. Recent genetic and cell biological studies suggest that the primary cilium, a small microtubule-based structure found on the surface of vertebrate cells, provides an essential point of regulation for Shh signaling and plays a key role in hair morphogenesis. However, what regulates primary cilium formation both in vitro and during tissue homeostasis is poorly understood. This thesis provides evidence that Missing in Metastasis (MIM)-a Bin/Amphiphysin/Rvs (BAR)-domain protein involved in actin cytoskeletal remodeling-is a novel regulator of primary cilia maintenance, Shh signaling and hair follicle regeneration and thereby constitutes a critical node integrating cytoskeletal remodeling with epithelial-mesenchymal signaling during tissue morphogenesis. We initially identified MIM in a screen for Shh responsive genes and showed using gain-of-function methods that it potentiates Shh signal transduction. Here we use loss-of-function methods to show that MIM is required for Shh responsiveness in primary epithelial and mesenchymal cells and acts by regulating ciliogenesis. Using an in vivo hair regeneration assay, we show that MIM is required in the mesenchymal compartment for primary cilia formation and de novo hair follicle regeneration. More generally, we demonstrate the utility of this system for rapid screening and identificatior of novel cell type specific regulators of hair follicle cycling and regeneration. In addition, we address the mechanism of MIM function in ciliogenesis and show that endogenous MIM localizes to the basal body where it regulates cilia elongation but not basal body specification in a BAR domain-independent manner. We show that Cortactin (CTTN), a binding partner of MIM that regulates actin cytoskeleton branching and polymerization, is also involved in ciliogenesis, but unlike MIM, is required for cilia disassembly. MIM and CTTN appear to have antagonistic roles during primary cilia formation, with the double knock-down restoring both cilia and Shh signaling back to wild type levels. Our findings suggest that actin cytoskeleton remodeling via MIM and CTTN might provide a timing mechanism to regulate assembly, maintenance and disassembly of this microtubule-based organelle.
|Advisor:||Oro, Anthony E.|
|School Location:||United States -- California|
|Source:||DAI-B 70/10, Dissertation Abstracts International|
|Keywords:||Cilia, Ciliogenesis, Dermal papilla, Hair follicle, Metastasis, Sonic hedgehog|
Copyright in each Dissertation and Thesis is retained by the author. All Rights Reserved
The supplemental file or files you are about to download were provided to ProQuest by the author as part of a
dissertation or thesis. The supplemental files are provided "AS IS" without warranty. ProQuest is not responsible for the
content, format or impact on the supplemental file(s) on our system. in some cases, the file type may be unknown or
may be a .exe file. We recommend caution as you open such files.
Copyright of the original materials contained in the supplemental file is retained by the author and your access to the
supplemental files is subject to the ProQuest Terms and Conditions of use.
Depending on the size of the file(s) you are downloading, the system may take some time to download them. Please be