Date of Award

Summer 8-15-2010

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Developmental, Regenerative, & Stem Cell Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

The differentiation from mucous neck cells (NCs) to digestive-enzyme-secreting zymogenic cells (ZCs) in stomach is key for epithelial cell homeostasis and important in disease because disruption in ZC development leads to metaplasia, which is a precursor of stomach cancer. However, transcriptional regulation of the transition from NC to ZC has not been well studied. Our laboratory previously showed that the transcription factor (TF) MIST1 is required for normal ZC granulogenesis. The TF XBP1 binds and induces Mist1 gene expression in vitro and expands ER in other cell types. We hypothesized XBP1 might activate Mist1 and govern ZC differentiation as a whole.

Xbp1 was inducibly deleted in mice using a tamoxifen/Cre-loxP system. Tamoxifen induced deletion of Xbp1 (Xbp1Δ) abrogated nearly the entire structural development of ZCs including cell size and shape, granulogenesis, and elaboration of rER. XBP1 directly bound the Mist1 promoter, and was required and sufficient for transcriptional activation of MIST1. XBP1 deficient ZCs still induced ZC markers, but could not extinguish expression of NC markers.

Cre recombinase has been shown to cause genotoxicity even in the absence of loxP-flanked genes due to cryptic loxP sites in the mammalian genome. We report that tamoxifen induction of high level Cre alone caused atrophy of the entire epithelium with foci of hyperplasia by 2 weeks. Cre induction caused genotoxicity with apoptosis and increased levels of DNA damage markers (γH2AX, p53, DDIT3, GADD45A). Although Cre was expressed globally using an actin promoter, the effects were almost entirely stomach-specific. Despite severe injury, a subset of mice showed near complete recovery of the gastric mucosa 11-12 weeks after Cre induction.

We also discovered that tamoxifen by itself could cause transient, reversible metaplasia within 2 days after injection. Surprisingly, the metaplastic changes were fully reversed by 14 days following injection. This system allowed us to begin to determine pathways involved in inducing gastric metaplasia. The effects of tamoxifen were partially rescued by co-injecting indomethacin, a cyclooxygenase (Cox, aka Ptgs) inhibitor. Experiments using Ptgs1 and Ptgs2 null mice verified that Cyclooxygenase2 but not Cyclooxygenase1 was required for metaplasia.

Collectively, this study has revealed the role of XBP1 in NC to ZC differentiation via MIST1 regulation, and also has provided novel animal models for studying metaplasia and injury induction and recovery in gastric epithelium.

Language

English (en)

Chair and Committee

James JD Hsieh

Committee Members

Emily HY Cheng, Paul A Gray

Comments

Permanent URL: https://doi.org/10.7936/K76T0JTR

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