Elf3 encodes a novel 200-kD beta-spectrin: role in liver development

beta-spectrins are crucial for the maintenance of cell shape, the establish ment of cell polarity, and the formation of distinct membrane domains. Our strategy for identifying genes important for hepatocyte polarity has been t o utilize subtractive hybridization of early embryonic mouse cDNA liver lib raries. As a result,,ve have cloned three isoforms of a novel beta-spectrin elf (embryonic liver beta-fodrin), and here we report the analysis of elf3 , the longest isoform (8172 nt), ELF3 comprises 2154 residues with an overa ll similarity of 89.0% and 95.3% to mouse beta-spectrin (beta SpII Sigma 1) at the nucleotide and amino acid level, respectively. ELF3 is characterize d by an actin-binding domain, a long repeat domain, and a short regulatory domain remarkable for the absence of a PH domain, Linkage analysis reveals that elf3 maps to mouse chromosome 11 between D11Bir6 and D11Xrf477, a diff erent chromosomal locus from that of the other four spectrin genes, Norther n blot analysis utilizing an elf3 3'-UTR probe demonstrates an abundant 9.0 -kb transcript in brain, liver, and heart tissues. Western blot with a poly clonal antibody against ELF identifies a 200 kD protein in mouse liver, bra in, kidney, and heart tissues. Immunohistochemical studies demonstrate ELF labeling of the basolateral or sinusoidal membranes surface as well as a gr anular cytoplasmic pattern in hepatocytes, Antisense studies utilizing cult ured liver explants show a vital role of elf3 in hepatocyte differentiation and intrahepatic bile duct formation, The differential expression, tissue localization, and functional studies demonstrate the importance of elf3 in modulating interactions between various components of the cytoskeleton prot eins controlling liver and bile duct development.