a–b, Immunostaining for PECAM and KLF2 (a) or KLF4 (b) is shown for cerebral vessels in individuals without CCM disease (“control”, left), for CCM lesions arising due to germline mutations in KRIT1 or PDCD10 (“familial”, middle), and for sporadic CCM lesions from two individuals (“sporadic”, right). Arrows indicate nuclear KLF2-high and nuclear KLF4-high endothelial cells in the CCM lesions. The red asterisk indicates fluorescence due to trapped intravascular erythrocytes. Scale bars, 50 μm. c, Schematic representation of the CCM2 CCCT duplication (“CCM2 CCCTdup”). d, CCM2 CCCTdup does not bind MEKK3. The indicated proteins were expressed in HEK293T cells, immunoprecipitated using anti-HA antibodies, and immunoblotted using the indicated antibodies. e, CCM2 CCCT dup binds KRIT1 and PDCD10 like wild-type CCM2. The indicated proteins were expressed and co-immunoprecipitated as described in (c). The results shown are representative of at least 3 separate experiments.