Table 2.

Predictions and results to distinguish between two models for furrow ingression

Bundled MTs in spindle midzone CS on furrow Long spindle [e.g. par-2(+)] Example Prediction: spindle length model Prediction: CS on furrow model Actual
Yes Yes Yes Wild type + + +
Yes Yes No par-2 + + +
No Yes Yes car-1 + + +
No Yes No car-1 par-2 - + +
No No Yes zen-4 + + +
No No No zen-4 gpr-1/2 - - -
  • In the first three columns, yes/no represents the presence (yes) or absence (no) of bundled microtubules (MTs) in the spindle midzone, centralspindlin (CS) on the furrow or long (yes) or short (no) spindles. In the last three columns, ± represents the ability to furrow. A spindle length model predicts that furrowing occurs in the absence of the microtubule bundles in the midzone when the spindle is long [i.e. >20 microns (Dechant and Glotzer, 2003)], and does not depend on the presence of CS on the furrow. However, our observations suggest a model that, in the absence of MTs in the midzone, furrowing depends on the presence of CS on the furrow and not spindle length