Abstract
The human apical protein CRB3 (Crb3 in mouse) organizes epithelial cell polarity. Loss of CRB3 expression increases the tumorogenic potential of cultured epithelial cells and favors metastasis formation in nude mice. These data emphasize the need of in vivo models to study CRB3 functions. Here, we report the phenotypic analysis of a novel Crb3 knockout mouse model. Crb3-deficient newborn mice show improper clearance of airways, suffer from respiratory distress and display perinatal lethality. Crb3 is also essential to maintain apical membrane identity in kidney epithelial cells. Numerous kidney cysts accompany these polarity defects. Impaired differentiation of the apical membrane is also observed in a subset of cells of the intestinal epithelium. This results in improper remodeling of adhesive contacts in the developing intestinal epithelium, thereby leading to villus fusion. We also noted a strong increase in cytoplasmic β-catenin levels in intestinal epithelial cells. β-catenin is a mediator of the Wnt signaling pathway, which is overactivated in the majority of colon cancers. In addition to clarifying the physiologic roles of Crb3, our study highlights that further functional analysis of this protein is likely to provide insights into the etiology of diverse pathologies, including respiratory distress syndrome, polycystic kidney disease and cancer.
Highlights
Cells is organized along an apical-basal axis
We modified the Crb[3] locus in mouse embryonic stem (ES) cells by homologous recombination using a targeting vector in which exon 2 was flanked by a loxP site and a loxP/FRT Neo cassette (Fig. 1a)
MRNA molecules containing exon 2 were less abundant in Crb3+/− heterozygous animals and undetectable in Crb3−/− mutant mice (Fig. 2a)
Summary
Cells is organized along an apical-basal axis. The apical domain faces a lumen and constitutes an important site of absorption and secretion, whereas the lateral domain spans across the plan of the epithelium and supports crucial adhesive and signaling cell-cell interactions[1]. CRB3A contributes to the establishment of functional TJ in cultured epithelial cells[21,25,26], and is important for establishment of apical-basal polarity. Similar to CRB3A, PALS1 and PATJ have been implicated in epithelial polarity as well as TJ formation[26,29,30,31] This suggests that these proteins are crucial mediators of CRB3A functions. This premise is coherent with the fact that the PBM of CRB3A is necessary for apical-basal polarity establishment and TJ biogenesis[25,26]. We describe a novel conditional Crb[3] mouse knockout model, which confirms that constitutive loss of Crb[3] is deleterious for epithelial tissue morphogenesis in lungs, kidneys and intestine. Our findings indicate that Crb[3] supports epithelial tissue morphogenesis and organ physiology in vivo
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