Worms lacking α-spectrin (right) do not elongate.

All multicellular animals examined have a spectrin cytoskeleton, suggesting that it serves some important, although so far poorly understood, function. On page 665, Norman and Moerman provide significant new insights into spectrin activity in C. elegans, where the tetrameric molecule seems to be required for normal development of body wall muscle and muscle attachment structures.

The authors identified and characterized spc-1, the only α spectrin gene in C. elegans. Localization of α spectrin to the cell membrane during development requires β spectrin, but not βHeavy spectrin. A null mutation in spc-1 blocks complete elongation of the worm embryo, which dies shortly after hatching. Elongation appears to be required for normal muscle development, and worms with mutations in spectrin genes develop a disorganized apical actin cytoskeleton in the hypodermis and broad muscle cells with misshapen myofilaments.

Surprisingly, the absence of spectrin does not appear to cause the broad muscle cell shape directly. Instead, the absence of spectrin in the hypodermis interferes with microfilament stability, which in turn interferes with the early elongation of the embryo. Broad muscle cells are a result of this failure in elongation. The authors' new genetic system should facilitate further dissection of complex interactions between tissues during development. ▪