Epidermal homeostasis requires a proper balance between proliferation and differentiation which when altered can lead to hyperproliferative disorders such as squamous cell carcinomas. Regulators of this process may include RNA degradation enzymes such as the exosome which is composed of 11 subunits. We have recently shown that exosome subunits such as EXOSC9, EXOSC7, and EXOSC10 are essential for maintaining epidermal self-renewal by promoting the mRNA degradation of differentiation specific transcription factors in progenitor cells. It is currently unknown the function of the other 8 subunits of the exosome as well as their associated adaptor proteins. Objective/hypothesis: This proposal seeks to understand the gene regulatory mechanisms involved in maintaining normal epidermal homeostasis. We hypothesize that exosome subunits exist in epidermal cells in subcomplexes with distinct functions. Subcomplexes such as EXOSC9, EXOSC7, and EXOSC10 are necessary to maintain progenitor function while other subcomplexes are necessary for differentiation. We also hypothesize that adaptor proteins recruit distinct exosome subcomplexes to target RNAs to either maintain self-renewal or to promote epidermal differentiation.
Specific Aims : (1) To determine the role of the exosome subunits in epidermal homeostasis and (2) to determine the role of exosome associated adaptor proteins in epidermal homeostasis. Study Design: To study epidermal homeostasis in a more clinically relevant setting, we established new methods to introduce specific combinations of genetic elements into 3- dimensionally intact human skin, containing human epidermal cells in the context of human dermal stroma and basement membrane, regenerated on immune deficient mice. By using this model, we can perform loss of function experiments on exosome subunits and adaptor proteins in regenerated human skin to characterize their role in epidermal growth and differentiation. We will also use RNA immunoprecipitations followed by next generation sequencing to determine the RNAs associated with exosome subunits as well as adaptor proteins.

Public Health Relevance

Abnormalities in epidermal growth and differentiation result in a wide range of disorders including psoriasis, squamous cell carcinoma, basal cell carcinoma and chronic wounds that negatively impact a large proportion of the U.S. population. This proposal seeks to understand the underlying molecular mechanisms that govern epidermal growth and differentiation. The efforts of this proposal will define the role of exosome subunits and adaptor proteins in epidermal homeostasis, which may yield insights in the development of therapies for epidermal disorders.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
Research Project (R01)
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Arthritis, Connective Tissue and Skin Study Section (ACTS)
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Baker, Carl
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University of California San Diego
Internal Medicine/Medicine
Schools of Medicine
La Jolla
United States
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Noutsou, Maria; Li, Jingting; Ling, Ji et al. (2017) The Cohesin Complex Is Necessary for Epidermal Progenitor Cell Function through Maintenance of Self-Renewal Genes. Cell Rep 20:3005-3013
Li, Jingting; Sen, George L (2016) Post-Transcriptional Mechanisms Regulating Epidermal Stem and Progenitor Cell Self-Renewal and Differentiation. J Invest Dermatol 136:746-752
Wang, Ying; Arribas-Layton, Marc; Chen, Yifang et al. (2015) DDX6 Orchestrates Mammalian Progenitor Function through the mRNA Degradation and Translation Pathways. Mol Cell 60:118-30