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First published online 9 July 2008
doi: 10.1242/dev.015289
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1 Department of Molecular, Cell, and Developmental Biology, Sinsheimer
Laboratories, University of California, Santa Cruz, CA 95064, USA.
2 Division of Biological Sciences, University of California San Diego, La Jolla,
CA 92093, USA.
3 Howard Hughes Medical Institute, University of California San Diego, La Jolla,
CA 92093, USA.
Author for correspondence (e-mail:
chisholm{at}ucsd.edu)
Accepted 11 June 2008
The F-spondin family of extracellular matrix proteins has been implicated in axon outgrowth, fasciculation and neuronal cell migration, as well as in the differentiation and proliferation of non-neuronal cells. In screens for mutants defective in C. elegans embryonic morphogenesis, we identified SPON-1, the only C. elegans member of the spondin family. SPON-1 is synthesized in body muscles and localizes to integrin-containing structures on body muscles and to other basement membranes. SPON-1 maintains strong attachments of muscles to epidermis; in the absence of SPON-1, muscles progressively detach from the epidermis, causing defective epidermal elongation. In animals with reduced integrin function, SPON-1 becomes dose dependent, suggesting that SPON-1 and integrins function in concert to promote the attachment of muscles to the basement membrane. Although spon-1 mutants display largely normal neurite outgrowth, spon-1 synergizes with outgrowth defective mutants, revealing a cryptic role for SPON-1 in axon extension. In motoneurons, SPON-1 acts in axon guidance and fasciculation, whereas in interneurons SPON-1 maintains process position. Our results show that a spondin maintains cell-matrix adhesion in multiple tissues.
Key words: Spondin, Extracellular matrix, Cell adhesion, Morphogenesis, Axon guidance
