Initiation of Lumen Formation from Junctions via Differential Actomyosin Contractility Regulated by Dynamic Recruitment of Rasip1

Vascular lumens are essential for the dispersal of nutrients, oxygen, and immune cells throughout the body. De novo lumen formation necessitates the precise segregation of junctional proteins from apical surfaces. Direct visualization of this process and a comprehensive understanding on how the apical and junctional compartments are segregated and established remain elusive, due to the lack of visualizable systems, proper reporters and manipulative tools. Using zebrafish as an experimental model, we have established a wealth of molecular reporters, photo-convertible and optogenetic tools and combined them with genetic analyses to study the establishment of apical domains from pre-apical junctional complexes. Our study identified Rasip1 as one of the earliest apical proteins recruited, peripheralizing cortical contractility at the junctional patches by inhibiting NMII at the center, thereby initiating the outward flow of junctional complexes. After the establishment of the apical compartments, Rasip1 shuttles between junctions and the apical compartments to the high-tension sites and tunes down the local hyper contractility, restricting Cdh5 to junctions by suppressing apical contractility. Above all, the formation of de novo lumens and maintenance of junctional integrity depend on the precise control of contractility within the apical compartments and junctions, orchestrated by the dynamic recruitment of Rasip1.