Mutations in beta-spectrin disrupt axon outgrowth and sarcomere structure.
beta-Spectrin is a major component of the membrane skeleton, a structure found at the plasma membrane of most animal cells. beta-Spectrin and the membrane skeleton have been proposed to stabilize cell membranes, generate cell polarity, or localize specific membrane proteins. We demonstrate that the Caenorhabditis elegans homologue of beta-spectrin is encoded by the unc-70 gene. unc-70 null mutants develop slowly, and the adults are paralyzed and dumpy. However, the membrane integrity is not impaired in unc-70 animals, nor is cell polarity affected. Thus, beta-spectrin is not essential for general membrane integrity or for cell polarity. However, beta-spectrin is required for a subset of processes at cell membranes. In neurons, the loss of beta-spectrin leads to abnormal axon outgrowth. In muscles, a loss of beta-spectrin leads to disorganization of the myofilament lattice, discontinuities in the dense bodies, and a reduction or loss of the sarcoplasmic reticulum. These defects are consistent with beta-spectrin function in anchoring proteins at cell membranes.
Hammarlund
M
M
Department of Biology, University of Utah, Salt Lake City 84112-0840, USA.
Davis
W S
WS
Jorgensen
E M
EM
D000595:Amino Acid Sequence; D000818:Animals; D001369:Axons / Q000502:physiology* / Q000648:ultrastructure; D017173:Caenorhabditis elegans; D029742:Caenorhabditis elegans Proteins; D002462:Cell Membrane / Q000648:ultrastructure; D016764:Cell Polarity; D017931:DNA Primers; D018076:DNA, Complementary / Q000235:genetics; D004847:Epithelial Cells / Q000648:ultrastructure; D017238:Genes, Helminth; D017930:Genes, Reporter; D049452:Green Fluorescent Proteins; D007422:Intestines / Q000648:ultrastructure; D007425:Intracellular Membranes / Q000648:ultrastructure; D008164:Luminescent Proteins / Q000235:genetics; D008969:Molecular Sequence Data; D009154:Mutation; D012518:Sarcomeres / Q000502:physiology* / Q000648:ultrastructure; D017386:Sequence Homology, Amino Acid; D013049:Spectrin / Q000235:genetics*; D013572:Synaptic Vesicles / Q000502:physiology
D029742:Caenorhabditis elegans Proteins; D017931:DNA Primers; D018076:DNA, Complementary; D008164:Luminescent Proteins; C409166:unc-70 protein, C elegans; D013049:Spectrin; D049452:Green Fluorescent Proteins