ABSTRACT
Pinin (Pnn), a nuclear speckle-associated protein, has been shown to function in maintenance of epithelial integrity through altering expression of several key adhesion molecules. Here we demonstrate that Pnn plays a crucial role in small intestinal development by influencing expression of an intestinal homeobox gene, Cdx2. Conditional inactivation of Pnn within intestinal epithelia resulted in significant downregulation of a caudal type homeobox gene, Cdx2, leading to obvious villus dysmorphogenesis and severely disrupted epithelial differentiation. Additionally, in Pnn-deficient small intestine, we observed upregulated Tcf/Lef reporter activity, as well as misregulated expression/distribution of beta-catenin and Tcf4. Since regulation of Cdx gene expression has been closely linked to Wnt/beta-catenin signaling activity, we explored the possibility of Pnn's interaction with beta-catenin, a major effector of the canonical Wnt signaling pathway. Co-immunoprecipitation assays revealed that Pnn, together with its interaction partner CtBP2, a transcriptional co-repressor, was in a complex with beta-catenin. Moreover, both of these proteins were found to be recruited to the proximal promoter area of Cdx2. Taken together, our results suggest that Pnn is essential for tight regulation of Wnt signaling and Cdx2 expression during small intestinal development.
Subject(s)
Cell Adhesion Molecules/metabolism , Genes, Homeobox , Homeodomain Proteins/genetics , Intestine, Small/growth & development , Morphogenesis/genetics , Nuclear Proteins/metabolism , Transcription Factors/genetics , Animals , CDX2 Transcription Factor , Cell Adhesion Molecules/genetics , DNA-Binding Proteins , Embryo, Mammalian/metabolism , Homeodomain Proteins/metabolism , Mice , Nuclear Proteins/genetics , Signal Transduction , TCF Transcription Factors/genetics , TCF Transcription Factors/metabolism , Transcription Factors/metabolism , Up-Regulation , Wnt Proteins/genetics , Wnt Proteins/metabolism , beta Catenin/genetics , beta Catenin/metabolismABSTRACT
Purpose. To investigate the specific role of Pinin (Pnn) in the development of anterior eye segment in mice. Methods. Conditional inactivation of Pnn in the developing surface eye ectoderm and lens was achieved by creating mice carrying a Pnn null and a floxed Pnn allele as well as a Pax6-Cre-GFP (Le-Cre) transgene. The resultant Pnn conditional knockout mice were examined by histologic and immunohistologic approaches. Results. Pax6-Cre-mediated deletion of Pnn resulted in severe malformation of lens placode-derived tissues including cornea and lens. Pnn mutant corneal epithelium displayed the loss of corneal epithelial identity and appeared epidermis-like, downregulating corneal keratins (K12) and ectopically expressing epidermal keratins (K10 and K14). This squamous metaplasia of Pnn mutant corneal epithelium closely correlated with significantly elevated beta-catenin activity and Tcf4 level. In addition, Pnn inactivation also led to misregulated level of p68 RNA helicase in mutant corneal epithelium. Conclusions. These data indicate that Pnn plays an essential role in modulating and/or orchestrating the activities of major developmental factors of anterior eye segments.
