Genetic Ablation of Afadin Causes Mislocalization and Deformation of Paneth Cells in the Mouse Small Intestinal Epithelium

Abstract

Afadin is an actin filament-binding protein that acts cooperatively in cell adhesion with the cell adhesion molecule nectin, and in directional cell movement with the small G protein Rap1 in a nectin-independent manner. We studied the role of afadin in the organization of the small intestinal epithelium using afadin conditional gene knockout (cKO) mice. Afadin was localized at adherens junctions of all types of epithelial cells throughout the crypt-villus axis. Paneth cells were localized at the base of the crypt in control mice, but not confined there, and migrated into the villi in afadin-cKO mice. The distribution of other types of epithelial cells did not change significantly in the mutant mice. The Paneth cells remaining in the crypt exhibited abnormal shapes, were buried between adjacent cells, and did not face the lumen. In these cells, the formation of adherens junctions and tight junctions was impaired. Rap1 and EphB3 were highly expressed in control Paneth cells but markedly down-regulated in the afadin-deficient Paneth cells. Taken together, the results indicate that afadin plays a role in the restricted localization of Paneth cells at the base of the crypt by maintaining their adhesion to adjacent crypt cells and inhibiting their movement toward the top of villi.

Rap1 acts via multiple mechanisms to position Canoe/Afadin and adherens junctions and mediate apical-basal polarity establishment

“…Tissue-specific knockouts implicated Afadin in morphogenic events depending on cadherin function, including synaptogenesis (Beaudoin et al, 2012), lymphangiogenesis (Majima et al, 2013) and nephron lumen formation (Yang et al, 2013). In the intestine, Afadin is required for epithelial barrier function (Tanaka-Okamoto et al, 2011) and for maintaining adhesion between Paneth and intestinal crypt cells (Tanaka-Okamoto et al, 2014).…”

Rap1 acts via multiple mechanisms to position Canoe/Afadin and adherens junctions and mediate apical-basal polarity establishment

“…Tissue-specific knockouts implicated Afadin in morphogenic events depending on cadherin function, including synaptogenesis (Beaudoin et al, 2012), lymphangiogenesis (Majima et al, 2013) and nephron lumen formation (Yang et al, 2013). In the intestine Afadin is required for normal epithelial barrier function (Tanaka-Okamoto et al, 2011) and for maintaining adhesion between Paneth and intestinal crypt cells (Tanaka-Okamoto et al, 2014).…”

Afadin (AF6) in cancer progression: A multidomain scaffold protein with complex and contradictory roles

“…[ 83 ] Tissue‐specific afadin loss within the intestinal epithelium of mice resulted in the mis‐localization and deformation of Paneth cells in the small intestine. [ 84 ] Afadin deletion also impaired proper formation of AJs and TJs in the base of the crypts of the small intestine, thus further demonstrating the importance of afadin in AJ and TJ formation. [ 84 ] A reduction in Rap1 and EphB3 expression was also observed upon afadin knockout, hindering Paneth cell movement toward the top of villi and maintaining their adhesion to neighboring crypt cells.…”

“…[ 84 ] Afadin deletion also impaired proper formation of AJs and TJs in the base of the crypts of the small intestine, thus further demonstrating the importance of afadin in AJ and TJ formation. [ 84 ] A reduction in Rap1 and EphB3 expression was also observed upon afadin knockout, hindering Paneth cell movement toward the top of villi and maintaining their adhesion to neighboring crypt cells. [ 84 ] Knockout of afadin in the intestinal epithelia of mice after birth inhibited localization of nectin‐2 and 3 at apical junctions.…”

“…[ 84 ] A reduction in Rap1 and EphB3 expression was also observed upon afadin knockout, hindering Paneth cell movement toward the top of villi and maintaining their adhesion to neighboring crypt cells. [ 84 ] Knockout of afadin in the intestinal epithelia of mice after birth inhibited localization of nectin‐2 and 3 at apical junctions. However, it did not disrupt localization of other cell‐cell adhesion proteins such as ZO‐1 and E‐cadherin.…”