The gastric epithelium of mice and humans undergoes continuous renewal. Dysregulated proliferation is a common feature not only of gastric disease but of orally administered medication in general. Yet little is known about the molecular mechanisms that coordinate division, differentiation, and migration of gastric epithelial cells. The goal of the current proposal is to build on previous work that determined a global gene expression profile for both the gastric epithelial progenitor cell (GEP) and the acid-secreting parietal cell (PC), a differentiated gastric lineage that is thought to regulate GEP differentiation and division. GEPs preferentially express both the critical somatic growth regulating gene insulin-like growth factor I (IGF-I) and its receptor (IGF-Ir), whereas PCs are enriched for expression of the IGF-sequestering gene IGF binding protein 2 (IGFBP2).
The first aim of the current proposal is to test the hypothesis that PCs use IGFBP2 to control bioavailability of IGFs thereby regulating GEP proliferation. Mice will be generated whose parietal cells will exhibit transgenic forced expression of IGFBP2. In parallel, IGFBP2 will be conditionally ablated by generating mice with floxed IGFBP2 alleles and crossing these to mice with PC-specific expression of cre recombinase that have already been generated in the lab. Earlier work also revealed that >20% of the genes in the GEP expression profile are involved in mRNA processing; many have Drosophila homologs critical for polarity establishment and cell fate determination during embryogenesis.
The second aim of the proposal will be to characterize the role of RNA localization in gastric epithelial renewal. Tools will be developed to assess the subcellular location of 1) RNA localizing proteins (e.g., Mago-m and Y14, genes in the GEP expression profile); 2) mRNA species associated with the RNA localizing apparatus. To identify candidate localized mRNAs, antibodies against RNA localizing proteins will be used to immunoprecipitate all associated mRNAs and determine their identity by oligonucleotide array. In Drosophila, genes whose RNAs are localized (e.g., runt and hairy and various genes encoding homeodomains) are critical for differentiating cell fate of daughter cells in developing tissues. Identifying localized transcripts in the gastric epithelium may lead to a better molecular picture of how normal renewal occurs in adult mammalian tissue, which, in turn, would help us better characterize both the gastric epithelial injury response and, eventually, how neoplastic (i.e. abnormal) proliferation develops and might be prevented.
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