Rasip1-Mediated Rho GTPase Signaling Regulates Blood Vessel Tubulogenesis via Nonmuscle Myosin IINovelty and Significance

Vascular tubulogenesis is essential to cardiovascular development. Within initial vascular cords of endothelial cells (ECs), apical membranes are established and become cleared of cell-cell junctions, thereby allowing continuous central lumens to open. Rasip1 is required for apical junction clearance, as well as for regulation of Rho GTPase activity. However, it remains unknown how activities of different Rho GTPases are coordinated by Rasip1 to direct tubulogenesis

Feedback Regulation of Receptor-Induced Ca2+ Signaling Mediated by E-Syt1 and Nir2 at Endoplasmic Reticulum-Plasma Membrane Junctions

Endoplasmic reticulum (ER)-plasma membrane (PM) junctions are highly conserved subcellular structures. Despite their importance in Ca2+ signaling and lipid trafficking, the molecular mechanisms underlying the regulation and functions of ER-PM junctions remain unclear. By developing a genetically encoded marker that selectively monitors ER-PM junctions, we found that the connection between ER and PM was dynamically regulated by Ca2+ signaling. Elevation of cytosolic Ca2+ triggered translocation of E-Syt1 to ER-PM junctions to enhance ER-to-PM connection. This subsequently facilitated the recruitment of Nir2, a phosphatidylinositol transfer protein (PITP), to ER-PM junctions following receptor stimulation. Nir2 promoted the replenishment of PM phosphatidylinositol 4,5-bisphosphate (PIP2) after receptor-induced hydrolysis via its PITP activity. Disruption of the enhanced ER-to-PM connection resulted in reduced PM PIP2 replenishment and defective Ca2+ signaling. Altogether, our results suggest a feedback mechanism that replenishes PM PIP2 during receptor-induced Ca2+ signaling via the Ca2+ effector E-Syt1 and the PITP Nir2 at ER-PM junctions