Desmosomes regulate keratinocyte actin dynamics in basal progenitors to promote epidermal development

Summary: Abstract Body: Desmoglein 1 (Dsg1), a desmosomal cadherin expressed only in stratified tissues, is necessary for coordinating mechanical and chemical signals to create a multilayered epidermal barrier. We showed that Dsg1 expression in vitro in a subset of basal keratinocyte progenitors promotes differentiation by coordinating Erk inhibition with redistribution of cortical actin tension along the plasma membrane, promoting delamination. Consistent with a role for Dsg1 in stratification, Dsg1 knock out (KO) mouse embryos displayed decreased epidermal thickness at E14.5-E15.5, recovering at E16.5. To find pathways involved in stratification, we performed single cell RNA-seq on Dsg1KO and WT embryos at stages E14.5, E15.5, E16.5 and E18.5, building a developmental atlas (62,459 KO, 39,102 WT cells). Using top gene markers, we identified 8 cell types and 6 keratinocyte subclusters. Differential gene expression analysis of the E18.5 basal II and K14+/K10+ transitional populations revealed significant downregulation of actin modulators including the transcription factor, serum response factor (SRF), and downstream effectors like RhoA, Vinculin, Filamin A and Arp3 (p < 0.05), the latter which we showed to be important for Dsg1-dependent delamination in vitro. Towards defining how Dsg1 regulates Arp3, protein interaction studies revealed the SH2/SH3 adaptor and N-WASP activator Nck1 as a Dsg1 binding partner. Silencing N-WASP or Nck1 reduced Dsg1-mediated stratification 3-fold, which expression of a Nck1 binding deficient mutant Dsg1Y1042F was unable to rescue, presumably through inability to activate N-WASP/Arp2/3-dependent actin remodeling. In accordance, Arp3 membrane recruitment by Dsg1Y1042F was decreased 3-fold. These studies support the idea that Dsg1 modulates actin dynamics in basal and transitional populations through transcriptional and post-translational mechanisms to promote epidermal development. Lisa M. Godsel^{1, 2}, Brieanna Jarrell¹, Ziyou Ren², Marihan Hegazy¹, Rosemary DiDominicis¹, Xin Tong¹, Jennifer Koetsier¹, Dongmei Wang¹, Rui Yi^{1, 2}, Kathleen Green^{1, 2} 1. Pathology, Northwestern University Feinberg School of Medicine, Chicago, IL, United States. 2. Dermatology, Northwestern University Feinberg School of Medicine, Chicago, IL, United States. Epidermal Structure and Barrier Function