Investigating the Mechanism of Hair Follicle Placode Induction : A novel approach to understanding establishment of the periodic pattern - In the field of regenerative medicine, while much work has been done to grow skin in culture, it has been especially difficult to create cultured skin that is able to autonomously produce hair follicles in a biologically accurate fashion. Optimizing a way to grow fully functional skin in culture would revolutionize the way that the medical field utilizes skin grafts and transplants. Especially in instances where there is insufficient transplant tissue to sample from, patients with severe burns, slow healing wounds, and advanced forms of scarring alopecia would greatly benefit from being able to receive skin grafts and transplants derived from fully functional skin produced in culture. Somehow, skin possesses an inherent ability to transform itself from a uniform sheet of tissue to an elegantly decorated structure with all of its necessary appendages organized in a periodic pattern. Several studies have been done to generate isolated follicle-like structures and even to stimulate a patch of hair growth in stem-cell derived tissue. The few instances of induced hair growth that have been accomplished in culture fall short of recapitulating hair follicle patterning de novo. We believe that better understanding how hair follicles establish a periodic pattern during development will provide a strong framework for creating a way to mimic this phenomenon in culture. In the developmental biology field, the prevailing hypotheses that have been proposed to explain periodic pattern establishment rely heavily on local signaling and self-organization. Though, there is insufficient experimental evidence to definitively support these hypotheses, which is also reflected in the challenging feat to produce skin with hair follicles in culture. Data from our lab utilizing live imaging of embryonic skin development has uncovered remarkable plasticity in hair follicle placode induction, revealing an underlying program that ensures robust development of a periodic pattern. Informed by this data, I hypothesize that long- distance migration mediated by Wnt signaling serves as the underlying mechanism for hair follicle placode induction rather than being driven entirely by local activation and inhibition by diffusible ligands. I plan to test this hypothesis by utilizing the Cre-Lox system under the control of a K14 epithelial-specific promoter to stochastically knock out beta-catenin, an important Wnt signaling transcription factor. In this way, Wnt responsiveness will be mosaic in that some cells will be Wnt-responsive and others will not. I will then characterize hair follicle placodes in the mosaic Wnt-responsive system (Aim 1), determine the mechanism for how Wnt-responsive cells are able to migrate and coalesce to form a placode (Aim 2), and determine how Wnt signaling output is refined from a stochastic to periodic pattern in an unperturbed environment (Aim 3). This proposed project will provide experimental evidence that has the potential to both lay the mechanistic foundation for more realistic skin culture experiments and challenge long-standing hypotheses in the field. Through collaboration between Princeton University, Robert Wood Johnson, and Weill Cornell Medicine, the proposed project and training plan is designed to provide the clinical, basic science training, mentorship, and resources necessary to accomplish this goal.
