sma-1 encodes a betaH-spectrin homolog required for Caenorhabditis elegans morphogenesis.
Morphogenesis transforms the C. elegans embryo from a ball of cells into a vermiform larva. During this transformation, the embryo increases fourfold in length; present data indicates this elongation results from contraction of the epidermal actin cytoskeleton. In sma-1 mutants, the extent of embryonic elongation is decreased and the resulting sma-1 larvae, although viable, are shorter than normal. We find that sma-1 mutants elongate for the same length of time as wild-type embryos, but at a decreased rate. The sma-1 mutants we have isolated vary in phenotypic severity, with the most severe alleles showing the greatest decrease in elongation rate. The sma-1 gene encodes a homolog of betaH-spectrin, a novel beta-spectrin isoform first identified in Drosophila. sma-1 RNA is expressed in epithelial tissues in the C. elegans embryo: in the embryonic epidermis at the start of morphogenesis and subsequently in the developing pharynx, intestine and excretory cell. In Drosophila, betaH-spectrin associates with the apical plasma membrane of epithelial cells; beta-spectrin is found at the lateral membrane. We propose that SMA-1 is a component of an apical membrane skeleton in the C. elegans embryonic epidermis that determines the rate of elongation during morphogenesis.
McKeown
C
C
Department of Molecular Genetics and Cell Biology, University of Chicago, Chicago, IL 60637, USA.
Praitis
V
V
Austin
J
J
D000595:Amino Acid Sequence; D000818:Animals; D001824:Body Constitution; D017173:Caenorhabditis elegans / Q000196:embryology*; D003001:Cloning, Molecular; D004330:Drosophila / Q000235:genetics; D029721:Drosophila Proteins; D005260:Female; D017238:Genes, Helminth; D015801:Helminth Proteins / Q000145:classification / Q000235:genetics*; D019476:Insect Proteins / Q000235:genetics; D007814:Larva; D008018:Life Cycle Stages; D008297:Male; D008969:Molecular Sequence Data; D009024:Morphogenesis / Q000235:genetics; D009154:Mutation; D017422:Sequence Analysis, DNA; D017386:Sequence Homology, Amino Acid; D013049:Spectrin / Q000145:classification / Q000235:genetics*
D029721:Drosophila Proteins; D015801:Helminth Proteins; D019476:Insect Proteins; C112961:kst protein, Drosophila; D013049:Spectrin