Blood vessel tubulogenesis requires Rasip1 regulation of GTPase signaling.
Cardiovascular function depends on patent blood vessel formation by endothelial cells (ECs). However, the mechanisms underlying vascular "tubulogenesis" are only beginning to be unraveled. We show that endothelial tubulogenesis requires the Ras interacting protein 1, Rasip1, and its binding partner, the RhoGAP Arhgap29. Mice lacking Rasip1 fail to form patent lumens in all blood vessels, including the early endocardial tube. Rasipl null angioblasts fail to properly localize the polarity determinant Par3 and display defective cell polarity, resulting in mislocalized junctional complexes and loss of adhesion to extracellular matrix (ECM). Similarly, depletion of either Rasip1 or Arhgap29 in cultured ECs blocks in vitro lumen formation, fundamentally alters the cytoskeleton, and reduces integrin-dependent adhesion to ECM. These defects result from increased RhoA/ROCK/myosin II activity and blockade of Cdc42 and Rac1 signaling. This study identifies Rasip1 as a unique, endothelial-specific regulator of Rho GTPase signaling, which is essential for blood vessel morphogenesis.
PubMed ID: 21396893
PMC ID: PMC3078994
Grant support: DK079862 NIDDK NIH HHS , GM007062 NIGMS NIH HHS , HL59373 NHLBI NIH HHS , R01 HL059373-12 NHLBI NIH HHS
Genes referenced: arhgap1 arhgap29 cdc42 ephb4 gja5 kdr pard3 rac1 rasip1 rho rhoa sacs
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|Figure 1. Rasip1 Is Essential for Vascular Tubulogenesis in All Blood Vessels (A�D) Rasip1 expression is conserved in the embryonic vasculature across species shown by in situ hybridization: mouse (A, E9.5; B, E8.5 transverse section, left dorsal aorta), Xenopus tropicalis (C, st.30), and zebrafish (D, 24 hpf). (E�H) E9.5 littermate mouse embryos showing defects in Rasip1 / embryos (F) and yolk sacs (H). (I�L) Whole-mount Flk1-lacZ beta-galactosidase staining of Rasip1+/ (I and K) and Rasip1 / (J and L) yolk sacs (I and J) and embryonic heads (K and L), showing narrow Rasip1 / blood vessels that fail to remodel. (M�P) Connexin40 (Cx40 or Gja5) (M and N) or EphB4-lacZ (O and P) in littermate E9.5 Rasip1+/ and Rasip1 / yolk sacs (M and N) or embryos (O and P) showing failed arterial (M and N) and venous (O and P) differentiation in Rasip1 / vessels. (Q�Z0 ) Flk1-LacZ beta-galactosidase staining of littermate E8.5 (6 somite stage) Rasip1+/ and Rasip1 / embryos and tissues, in whole mount or section. (Q and R) Ventral views of E8.5 embryonic paired dorsal aortae. Anterior is up. (S�V) Transverse sections of E8.5 embryos, through the trunk region, posterior to the heart. (U and V) Close-up views, showing open lumens in Rasip1+/ ;Flk1-lacZ embryos (S and U) but lumenless cords in Rasip1 / ;Flk1-lacZ embryos (T and V). Sections through hearts of E8.5 (W and X), showing absence of a lumen in the endocardium of Rasip1 / ;Flk1-lacZ embryos (X). Yolk sacs in whole-mount (Y and Z) or section views (Y0 and Z0 ). Vascular tubes are absent in all Rasip1 / vessels examined. Arrows, dorsal aortae; Arrowheads, yolk sac vessels. Ys, yolk sac; Scale bars, 500 mm (A, E, F, G, and H), 250 mm (C), 200 mm (K�P), 100 mm (D, I, J, Q, R, Y, and Z), and 50 mm (B, S, T, U, V, W, X, Y, Z, Y0 , and Z0 ). See also Figures S1 and S2.|