LSR expression in adult mice. (A) Tissue sections of brain, lung, liver, and intestine were colabeled with antibodies directed against LSR (red) and CD31 (green, to label blood vessels). Expression of LSR in CD31⁺ ECs is only observed in the brain. Bar, 100 µm. (B) Tissue sections from adult mice were labeled with the blood vessel marker BSL I (green), and antibodies against occludin (blue, bicellular TJ) and LSR (red). The merged image indicates that in CNS blood vessels LSR is localized at the tricellular TJ where two bicellular TJ meet. Bar, 5 µm. (C, left) Quantitative real-time PCR analysis of LSR isoforms from purified brain ECs and liver ECs. Analysis indicates no detectable LSR expression in liver ECs but high expression of the α′ variant followed by α and β variants in brain ECs. (C, middle and right) Quantitative real-time PCR analysis of LSR variants from whole brain, lung, and liver. The expression in liver is much higher than brain or lung, and thus was given its own y axis (right). Splice variant composition is similar between brain and liver (α’ variant followed by α and β variants) but different in the lung (β variant followed by α’ and α variants). Data represent means ± SD (error bars) from three indipendent experiments. (D) Western blot profile of LSR from purified brain capillaries shows a stronger band for the α′ splice variant followed by α and β.