Epithelial tissues consist of various morphology of organ. Most of these organs contain lumen, which is surrounded by the apical surface of epithelial cells. Because lumen in epithelial tissues are known to serve to digest contents or to allow the movement of fluids or gases, its formation is one of the most important event in epithelial morphogenesis. It is known that epithelial cells form lumen de novo by following steps: (1) cell-matrix and cell-cell recognition, (2) apical-basal polarization, and (3) the expansion of the luminal space. We recently found that leucine-rich repeat kinase 1 (LRRK1), a member of ROCO family kinase, regulates the cell-cell adhesion and the mitotic spindle orientation. Because the cell-cell adhesion is required for proper cell-cell recognition and the spindle orientation is required for proper expansion of the luminal space, LRRK1 might play an important role in proper lumen formation. Indeed, knockdown of LRRK1 by siRNA causes multiple lumen formation. In this project, we attempt to identify the substrates for LRRK1 in this process and reveal how LRRK1 regulates de novo lumen formation in epithelial morphogenesis.

To understand the role of LRRK1 in de novo lumen formation, we focus on the LRRK1-regulated cell-cell adhesion and mitotic spindle orientation. We first attempt to identify the substrates for LRRK1 in these processes. We will search for substrates among LRRK1-interacting proteins, which were already identified by LC-MS/MS. We next attempt to examine the role of candidate substrates for LRRK1 in de novo lumen formation by using a 3D Madin Darby canine kidney (MDCK) cell-based system. When MDCK cells are cultured in matrigel, these cells form spherical cysts consisting of single-layered cells surrounding a central lumen. We try to reveal the role of identified substrates in lumen formation and the regulatory mechanism of de novo lumen formation mediated by LRRK1.

The regulation of mitotic spindle orientation and cell-cell adhesion is known to be required for several organ development. Our research also contributes to a better understanding of these morphogenesis.