Snail induces epithelial cell extrusion by regulating RhoA contractile signalling and cell–matrix adhesion

Abstract

Cell extrusion is a morphogenetic process that is implicated in epithelial homeostasis and elicited by stimuli ranging from apoptosis to oncogenic transformation. To explore if the morphogenetic transcription factor, Snail (SNAI1), induces extrusion, we inducibly expressed a stabilized Snail6SA transgene in confluent MCF-7 monolayers. When expressed in small clusters (<3 cells) within otherwise wild-type confluent monolayers, Snail6SA expression induced apical cell extrusion. In contrast, larger clusters or homogenous cultures of Snail6SA cells did not show enhanced apical extrusion, but eventually displayed sporadic basal delamination. Transcriptomic profiling revealed that Snail6SA did not substantively alter the balance of epithelial: mesenchymal genes. However, we identified a transcriptional network that led to upregulated RhoA signalling and cortical contractility in Snail6SA expressing cells. Enhanced contractility was necessary, but not sufficient, to drive extrusion, suggesting that it collaborates with other factors. Indeed, we found that the transcriptional downregulation of cell-matrix adhesion cooperates with contractility to mediate basal delamination. This provides a pathway for Snail to influence epithelial morphogenesis independently of classic Epithelial to Mesenchymal Transition.

The EMT transcription factor Snai1 maintains myocardial wall integrity by repressing intermediate filament gene expression

“…Studies in Drosophila embryos and in mammalian cells in culture have revealed the importance of cell extrusion in limiting tissue overcrowding and eliminating dying cells to maintain tissue homeostasis and/or determine cell fate ( Kocgozlu et al, 2016 ; Wee et al, 2020 ). Other experiments have shown that a contractile actomyosin ring around the cell cortex is necessary for their extrusion ( Rosenblatt et al, 2001 ; Eisenhoffer et al, 2012 ; Kocgozlu et al, 2016 ).…”

“…Using zebrafish as a model to analyse CM cytoskeletal organization at single-cell resolution, we searched for candidate transcription factors that regulate CM cytoskeletal and tissue integrity. Amongst the transcription factors involved in cardiac development, we focused on Snai1 ( Nieto, 2002 ; Nieto et al, 2016 ), whose orthologues regulate cytoskeletal remodelling and epithelial tissue integrity in Drosophila embryos ( Martin et al, 2010 ; Weng and Wieschaus, 2016 ) and in mammalian cells in culture ( Wee et al, 2020 ). During vertebrate heart formation, Snai1 has been implicated in myocardial precursor migration towards the midline ( Qiao et al, 2014 ) and in valve formation ( Tao et al, 2011 ), but a role in myocardial wall development, during which an epithelial-to-mesenchymal (EMT)-like process occurs ( Staudt et al, 2014 ; Jiménez-Amilburu et al, 2016 ; Priya et al, 2020 ), has not been reported.…”

The EMT transcription factor Snai1 maintains myocardial wall integrity by repressing intermediate filament gene expression

“…Using zebrafish as a model to analyze CM cytoskeletal organization at single-cell resolution, we searched for candidate transcription factors that regulate CM cytoskeletal and tissue integrity. Amongst the transcription factors involved in cardiac development, we focused on Snai1, whose orthologues regulate cytoskeletal remodeling and epithelial tissue integrity in Drosophila embryos and in mammalian cell culture 9–11 . Snai1 is required for the migration of myocardial precursors during heart tube formation 6 and for valve formation 5 , but a role in myocardial wall development has not been addressed.…”

“…Extensive studies in Drosophila embryos and in mammalian cell culture have revealed the importance of cell extrusion in limiting tissue overcrowding and eliminating dying cells to maintain tissue homeostasis and/or determine cell fate 11, 23, 24 . Other experiments have shown that a contractile actomyosin ring around the cortex of the cells is necessary for their extrusion 24–26 .…”

“…However, the identity of the transcriptional targets of Snai1 that promote cellular contractility in this system remains unknown. Recent in vitro studies have reported Snai1-mediated upregulation of active RhoA at the mRNA and protein levels, leading to increased cortical actomyosin and apical extrusion 11 . Here, our work uncovers a previously unsuspected role for the EMT-inducing factor Snai1 in limiting CM extrusions by regulating IF gene expression.…”