Assembly and maintenance of the architecture of the brush border microvilli: role of fimbrin and other actin-binding proteins
Zusammenfassung der Projektergebnisse
The brush border microvilli of intestinal epithelial cells (lECs) constitute an excellent model system for studying actin-based surface projection. In the IEC each microvillus is supported by an axial bundle of actin filaments extensively crosslinked by plastin-1, villin and espin. Studies on knockout mice demonstrated that none of several components (villin, ezrin, myosin 1a) is absolutely required for the formation of microvilli but the requirement of plastln-1 or espin has not been addressed. Our goal was to investigate the contribution and Interrelationship of cytoskeleton components, mainly plastin-1, to the assembly and maintenance of the architecture of the intestinal brush border using in vivo mouse models. We have undertaken a detailed morphological and functional characterization of a knockout mouse lacking plastin-1. Plastin-1 deficient mice did not show any overt phenotype but we observed alterations in the ultrastructure and composition of the brush border. These alterations result in increased fragility of the epithelium evidenced as increased sensitivity of the brush border to biochemical manipulations, decreased transepithelial resistance and increased sensitivity to dextran sodium sulphate-induced colitis. We concluded that plastin-1 constitutes an essential regulator of brush border morphology and stability through a novel role connecting actin filaments to the underlying intermediate filament network. To circumvent compensation mechanisms we have studied the role of actin-bundling proteins in double and triple knockouts of plastin-1, espin and villin. We have observed a strong growth delay in the triple knockout. These mice still develop apical microvilli in the intestinal brush border, but the precise paracristalline organisation of actin filaments is lost. This structural defect correlates with a highly inefficient apical targeting of cargoes that accumulate sub-apically. Finally, we have examined morphological and functional aspects of the inner ear to investigate the impact of the plastin-1 deficiency in this organ. Although plastin-1 is highly expressed in stereocilia, its absence does not affect the initial formation of stereoclliary bundles and there are no obvious defects in the structure of the stereocilia or cuticular plate in the organ of Corti. However, despite the apparent normal morphology of stereocilia in the plastin-1 knockout mice, hearing is compromised. Taken together our results will provide to a better understanding of the roles of actin-bundling proteins in diverse cellular structures and their contribution to the development of pathologic conditions.
Projektbezogene Publikationen (Auswahl)
- Origins and evolution of the actin cytoskeleton. Advances in Experimental Medicine and Biology 607, 7-110 (2007)
F. Rivero, F. Cvrčková
- Plastin 1 binds to keratin and is required for terminal web assembly in the intestinal epithelium. Molecular Biology of the Cell, 20:2549-2562 (2009)
E-M. S. Grimm-Günter, C. Revenu, S. Ramos, I. Hurbain, N. Smyth, E. Ferrary, D. Louvard, S. Robine, F. Rivero
