Analysis of 4.1R mRNA expression by Northern blot analysis. RNA isolated from tissues of a normal control mouse (left) and a homozygous 4.1 knockout mouse (right). Upper panel shows hybridization to a 4.1R cDNA probe representing sequences in exons 18–21, while lower panel shows hybridization to a control actin cDNA probe. Essentially identical results were obtained using a probe that spans exons 2–21. Source of RNA: lanes 1 and 6, heart; lanes 2 and 7, lung; lanes 3 and 8, skeletal muscle; lanes 4 and 9, brain; lanes 5 and 10, spleen. Position of RNA size standards of 9.4, 7.5, 4.4, 2.4, and 1.35 kb is indicated at the top right by the dashed lines.