April 2010

Document Type


Degree Name



Dept. of Cell and Developmental Biology


Oregon Health & Science University


Tissue regeneration after injury poses a major challenge that requires the fine balance between stimulation and dysregulation of cell proliferation in order to facilitate homeostatic repair. We have shown that fusion between circulating bone marrow-derived cells (BMDCs) and non-hematopoietic cells occurs in response to intestinal epithelial injury as a potential regenerative mechanism. We suggest that fusion also occurs in tumorigenesis based upon the observation of shared microenvironments between injury and tumor models. However, the cellular and environmental requirements for intestinal cell fusion remain unknown. Importantly, the physiologic impact of cell fusion on epithelial homeostasis and tumorigenesis has not been defined. Therefore, to investigate the physiologic relevance of this process in repair and disease, the work in this thesis will test the hypothesis that cell fusion hybrids represent a unique cellular population, retaining characteristics of both parental fusogenic populations. To test this hypothesis, I explored the microenvironmental mediators of cell fusion, identified the fusogenic cell populations within the BMDCs, and investigated and compared the transcriptome profile of cell fusion hybrids with their parental fusogenic cell types. Using both transplantation and parabiosis model systems, I identified two important environmental factors critical for mediating intestinal cell fusion: local inflammation and epithelial proliferation. Significantly, these factors characterize the regenerative and tumorigenic microenvironment. Further, temporal analysis of the cellular dynamics preceding epithelial cell fusion revealed that GFP-expressing donor cells traffic to the intestine and cluster around hyperproliferative intestinal crypts, forming a pre-fusion complex. Interestingly, these clusters were composed of differentiated macrophages, B and T cells. This result led to a systematic survey of the fusogenic potential of FACS-isolated discrete blood cell populations, where I determined that macrophages are a primary BMDC fusion partner. Finally, to investigate the physiologic potential of intestinal cell fusion hybrids, comparative transcriptome analysis of cell fusion hybrids, unfused epithelia and unfused macrophages revealed that epithelial-like cell fusion hybrids retain a portion of the macrophage transcriptional profile. Taken together, this work provides a significant foundation for understanding the mechanism of cell fusion as well as the overall physiologic impact of cell fusion on intestinal epithelial regeneration and tumorigenesis. Importantly, the implication of inflammation in the cell fusion process coupled with the unique transcriptional potential of cell fusion hybrids suggests a potential role for cell fusion in linking intestinal inflammatory diseases and cancer.




School of Medicine



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