Claudin-5, ABCG2, ABCC1 and ABCB1 in the early developing 4th ventricular choroid plexus at 7 wpc. Immunostaining of the emerging 4th ventricle choroid plexus at 7 wpc reveals claudin-5 in apical/luminal and basolateral membranes (A) and ABCG2 (B), ABCC1 (C), and ABCB1 (D) immunoreactivity in apical/luminal membranes of choroidal epithelial cells facing the 4th ventricle (4 V) and in the fenestrated vasculature (arrows) (A–D). Note also the immunostaining of parenchymal blood vessels (arrowheads) illustrating the blood-brain barrier proper. Figures shown from 2 individual embryos. Abbreviations: CHP: choroid plexus; cld-5: claudin-5; 4 V: fourth ventricle. WPC: weeks post conception. (A–D) Same magnification. Scale bar: 50 μm.