Spatial and temporal organization of cadherin in punctate adherens junctions

Abstract

<p id="d1835679e307">Adherens junctions (AJs) are major intercellular adhesive structures in vertebrates. Despite the critical role of AJs in tissue integrity and morphogenesis, the detailed organization of their key protein E-cadherin, inside and outside of AJs, remains controversial. Using superresolution microscopy approaches, we show that AJs can reach more than 1 μm in length and consist of tightly packed E-cadherin clusters with crystal-like density interspersed within sparser cadherin regions. No clusters were found outside of AJs. E-cadherin tracking showed that these crystal-like pAJ clusters are transient and their cadherin is reused for new clusters. Our results thus modify the classical view of AJs by depicting them as mosaics of cadherin clusters, whose short lifetimes enable stable overall morphology combined with rapid internal rearrangements. </p><p class="first" id="d1835679e310">Adherens junctions (AJs) play a fundamental role in tissue integrity; however, the organization and dynamics of the key AJ transmembrane protein, E-cadherin, both inside and outside of AJs, remain controversial. Here we have studied the distribution and motility of E-cadherin in punctate AJs (pAJs) of A431 cells. Using single-molecule localization microscopy, we show that pAJs in these cells reach more than 1 μm in length and consist of several cadherin clusters with crystal-like density interspersed within sparser cadherin regions. Notably, extrajunctional cadherin appears to be monomeric, and its density is almost four orders of magnitude less than observed in the pAJ regions. Two alternative strategies of tracking cadherin motion within individual junctions show that pAJs undergo actin-dependent rapid—on the order of seconds—internal reorganizations, during which dense clusters disassemble and their cadherins are immediately reused for new clusters. Our results thus modify the classical view of AJs by depicting them as mosaics of cadherin clusters, the short lifetimes of which enable stable overall morphology combined with rapid internal rearrangements. </p>