![]() ![]() Members of the spectrin gene family and their associated proteins have been identified in diverse tissues of vertebrates, echinoderms, and Drosophila melanogaster, suggesting that spectrin-based membrane skeletal structures are a ubiquitous feature of metazoan animal cells ( Bennett and Gilligan 1993 Thomas et al. ![]() Protein localization and in vitro studies make spectrin a likely candidate. Components important in this process are likely to include cytoskeletal proteins. Maintenance of tissue integrity, particularly in tissues that undergo constant stress, is critical to the survival of an organism. We hypothesize that heteromeric spectrin evolved in metazoans in response to the needs of cells in the context of mechanically integrated tissues that can withstand the rigors imposed by an active organism. elegans β-G spectrin is required for normal muscle and neuron function, but is dispensable for embryonic elongation and establishment of early epithelial polarity. Instead β-G spectrin-deficient nematodes arrest as early larvae with progressive defects in the musculature and nervous system. Contrary to recent speculation, β-G spectrin is not associated with internal membranes and depletion of β-G spectrin was not associated with any detectable defects in secretion. Strikingly, depletion of nematode β-G spectrin by RNA-mediated interference to undetectable levels does not affect the establishment of structural and functional polarity in epidermis and intestine. Nematode β-G spectrin associates with plasma membranes at sites of cell–cell contact, beginning at the two-cell stage, and with a dramatic increase in intensity after gastrulation when most cell proliferation has been completed. ![]() The expression patterns of nematode β-G spectrin and vertebrate β spectrins exhibit three striking parallels including: (1) β spectrins are associated with the sites of cell–cell contact in epithelial tissues (2) the highest levels of β-G spectrin occur in the nervous system and (3) β spec-trin-G in striated muscle is associated with points of attachment of the myofilament apparatus to adjacent cells. We propose that α spectrin combines with the β-G and β-H subunits to form α/β-G and α/β-H heteromers that perform the entire repertoire of spectrin function in the nematode. elegans α spectrin is reproduced by tandem depletion of both β-G and β-H spectrins. Our experiments show that the phenotype resulting from the loss of the C. The Caenorhabditis elegans genome encodes one α spectrin subunit, a β spectrin subunit (β-G), and a β-H spectrin subunit. ![]()
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