Lovejoy, M.; Rabino, A. F.; Gonzalez-Blotta, L.; Gangasani, V.; Durham, S. M.; Kreider, G.; Garcia-Mata, R.

Polarized epithelia are essential for organ function, and disruption of epithelial polarity is a hallmark of many diseases, including cancer. We previously showed that the RhoG-specific guanine nucleotide exchange factor SGEF interacts with the Scribble polarity complex to regulate epithelial junction assembly in 2D monolayers. However, its role in epithelial morphogenesis and lumen formation in 3D remains unknown. Here, we combined quantitative morphometric analysis with long-term live-cell imaging to investigate the role of SGEF during MDCK cyst development. SGEF KD disrupted normal lumenogenesis, producing enlarged cysts with multiple collapsed lumens accompanied by reduced E-cadherin, {beta}-catenin, and ZO-1 expression. Loss of SGEF also altered the distribution of the actomyosin network. Re-expression of WT SGEF restored the normal phenotype, whereas restoration of E-cadherin and ZO-1 partially rescued lumen architecture, identifying the loss of junction integrity as a key driver of the morphogenetic defects. Unexpectedly, live-cell imaging revealed increased motility and frequent cyst fusion in SGEF-KD cysts. Restoring E-cadherin levels abolished cyst migration, while inhibition of matrix metalloproteinases markedly restored normal cyst volume and lumen architecture, identifying extracellular matrix remodeling as an additional contributor to the SGEF-deficient phenotype. Together, these findings identify SGEF as a key regulator of epithelial morphogenesis, coordinating junction integrity, actomyosin organization, lumen formation, and collective migration.