A Cdh3 - b-Catenin - Laminin signaling axis by a subset of breast tumor leader cells controls leader cell polarization and directional collective migration

Carcinoma dissemination can occur when heterogeneous tumor and tumor stromal cells clusters migrate together via collective migration. Cells at the front lead and direct collective migration, yet how these leader cells form and interact with the microenvironment to direct migration are not fully appreciated. From live videos of primary mouse and human breast tumor organoids in a 3D microfluidic system that mimics native breast tumor microenvironment, we developed 3D computational models which hypothesize that leader cells generate high protrusive forces and overcome extracellular matrix (ECM) resistance. Using single cell sequencing, we reveal leader cells are heterogeneous, and we identify and isolate a unique Cadherin-3 (Cdh3) positive leader cell subpopulation necessary and sufficient to lead migration. Cdh3 controls leader cell protrusion dynamics and local production of Laminin-332 which is required for integrin/focal adhesion function. Our findings highlight how a subset of leader cells interact with the microenvironment to direct collective migration. Primary tumor organdoids from K14-Actin.GFP; MMTV-PyMT mice (pure FVB/n background) were isolated, cultured in a microphysiological system, migration was induced (biochemical or biomechanical), organoids were isolated and analyzed using scRNAseq.